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MySQL NDB Cluster 6.1-7.1


5.3.6 Defining MySQL Cluster Data Nodes

The [ndbd] and [ndbd default] sections are used to configure the behavior of the cluster's data nodes.

[ndbd] and [ndbd default] are always used as the section names whether you are using ndbd or (in MySQL Cluster NDB 6.4.0 and later) ndbmtd binaries for the data node processes.

There are many parameters which control buffer sizes, pool sizes, timeouts, and so forth. The only mandatory parameters are:

  • Either ExecuteOnComputer or HostName, which must be defined in the local [ndbd] section.

  • The parameter NoOfReplicas, which must be defined in the [ndbd default] section, as it is common to all Cluster data nodes.

Note

It is no longer strictly necessary to set NoOfReplicas starting with MySQL Cluster NDB 6.3.25 and MySQL Cluster NDB 7.0.6, where it acquires a default value (2). However, it remains good practice to set it explicitly.

Most data node parameters are set in the [ndbd default] section. Only those parameters explicitly stated as being able to set local values are permitted to be changed in the [ndbd] section. Where present, HostName, NodeId and ExecuteOnComputer must be defined in the local [ndbd] section, and not in any other section of config.ini. In other words, settings for these parameters are specific to one data node.

For those parameters affecting memory usage or buffer sizes, it is possible to use K, M, or G as a suffix to indicate units of 1024, 1024×1024, or 1024×1024×1024. (For example, 100K means 100 × 1024 = 102400.) Parameter names and values are currently case-sensitive.

Information about configuration parameters specific to MySQL Cluster Disk Data tables can be found later in this section (see Disk Data Configuration Parameters).

Beginning with MySQL Cluster NDB 6.4.0, all of these parameters also apply to ndbmtd (the multi-threaded version of ndbd). Two additional data node configuration parameters—MaxNoOfExecutionThreads and ThreadConfig—apply to ndbmtd only; these have no effect when used with ndbd. For more information, see Multi-Threading Configuration Parameters (ndbmtd). See also Section 6.3, “ndbmtd — The MySQL Cluster Data Node Daemon (Multi-Threaded)”.

Identifying data nodes.  The NodeId or Id value (that is, the data node identifier) can be allocated on the command line when the node is started or in the configuration file.

  • Id

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0unsigned[none]1 - 48IS

    A unique node ID is used as the node's address for all cluster internal messages. For data nodes, this is an integer in the range 1 to 48 inclusive. Each node in the cluster must have a unique identifier.

    NodeId is the preferred parameter name to use when identifying data nodes beginning with MySQL Cluster NDB 6.2.19, MySQL Cluster NDB 6.3.39, MySQL Cluster NDB 7.0.20, and MySQL Cluster NDB 7.1.9. Although Id continues to be supported for backward compatibility, it is now deprecated and generates a warning when used.

  • NodeId

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0unsigned[none]1 - 48IS

    A unique node ID is used as the node's address for all cluster internal messages. For data nodes, this is an integer in the range 1 to 48 inclusive. Each node in the cluster must have a unique identifier.

    NodeId is the preferred parameter name to use when identifying data nodes beginning with MySQL Cluster NDB 6.2.19, MySQL Cluster NDB 6.3.39, MySQL Cluster NDB 7.0.20, and MySQL Cluster NDB 7.1.9. Although Id continues to be supported for backward compatibility, it is now deprecated and generates a warning when used.

  • ExecuteOnComputer

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0name[none]...S

    This refers to the Id set for one of the computers defined in a [computer] section.

  • HostName

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0name or IP addresslocalhost...N

    Specifying this parameter defines the hostname of the computer on which the data node is to reside. To specify a hostname other than localhost, either this parameter or ExecuteOnComputer is required.

  • ServerPort

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0unsigned[none]1 - 64KS

    Each node in the cluster uses a port to connect to other nodes. By default, this port is allocated dynamically in such a way as to ensure that no two nodes on the same host computer receive the same port number, so it should normally not be necessary to specify a value for this parameter.

    However, if you need to be able to open specific ports in a firewall to permit communication between data nodes and API nodes (including SQL nodes), you can set this parameter to the number of the desired port in an [ndbd] section or (if you need to do this for multiple data nodes) the [ndbd default] section of the config.ini file, and then open the port having that number for incoming connections from SQL nodes, API nodes, or both.

    Note

    Connections from data nodes to management nodes is done using the ndb_mgmd management port (the management server's PortNumber; see Section 5.3.5, “Defining a MySQL Cluster Management Server”) so outgoing connections to that port from any data nodes should always be permitted.

  • TcpBind_INADDR_ANY

    Setting this parameter to TRUE or 1 binds IP_ADDR_ANY so that connections can be made from anywhere (for autogenerated connections). The default is FALSE (0).

    This parameter was added in MySQL Cluster NDB 6.2.0.

  • NodeGroup

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.4.0 [none]0 - 65536IS

    This parameter can be used to assign a data node to a specific node group. It is read only when the cluster is started for the first time, and cannot be used to reassign a data node to a different node group online. It is generally not desirable to use this parameter in the [ndbd default] section of the config.ini file, and care must be taken not to assign nodes to node groups in such a way that an invalid numbers of nodes are assigned to any node groups.

    The NodeGroup parameter is chiefly intended for use in adding a new node group to a running MySQL Cluster without having to perform a rolling restart. For this purpose, you should set it to 65536 (the maximum value). You are not required to set a NodeGroup value for all cluster data nodes, only for those nodes which are to be started and added to the cluster as a new node group at a later time. For more information, see Section 7.13.3, “Adding MySQL Cluster Data Nodes Online: Detailed Example”.

    This parameter was added in MySQL Cluster NDB 6.4.0.

  • NoOfReplicas

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer[none]1 - 4IS
    NDB 6.3.25integer21 - 4IS
    NDB 7.0.6integer21 - 4IS

    This global parameter can be set only in the [ndbd default] section, and defines the number of replicas for each table stored in the cluster. This parameter also specifies the size of node groups. A node group is a set of nodes all storing the same information.

    Node groups are formed implicitly. The first node group is formed by the set of data nodes with the lowest node IDs, the next node group by the set of the next lowest node identities, and so on. By way of example, assume that we have 4 data nodes and that NoOfReplicas is set to 2. The four data nodes have node IDs 2, 3, 4 and 5. Then the first node group is formed from nodes 2 and 3, and the second node group by nodes 4 and 5. It is important to configure the cluster in such a manner that nodes in the same node groups are not placed on the same computer because a single hardware failure would cause the entire cluster to fail.

    If no node IDs are provided, the order of the data nodes will be the determining factor for the node group. Whether or not explicit assignments are made, they can be viewed in the output of the management client's SHOW command.

    Prior to MySQL Cluster NDB 6.3.25 and MySQL Cluster NDB 7.0.6, there was no default value for NoOfReplicas; beginning with these versions, the default value is 2, which is the recommended setting in most common usage scenarios. (Bug #44746)

    The maximum possible value is 4; currently, only the values 1 and 2 are actually supported.

    Important

    Setting NoOfReplicas to 1 means that there is only a single copy of all Cluster data; in this case, the loss of a single data node causes the cluster to fail because there are no additional copies of the data stored by that node.

    The value for this parameter must divide evenly into the number of data nodes in the cluster. For example, if there are two data nodes, then NoOfReplicas must be equal to either 1 or 2, since 2/3 and 2/4 both yield fractional values; if there are four data nodes, then NoOfReplicas must be equal to 1, 2, or 4.

  • DataDir

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0path....IN

    This parameter specifies the directory where trace files, log files, pid files and error logs are placed.

    The default is the data node process working directory.

  • FileSystemPath

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0pathDataDir...IN

    This parameter specifies the directory where all files created for metadata, REDO logs, UNDO logs (for Disk Data tables), and data files are placed. The default is the directory specified by DataDir.

    Note

    This directory must exist before the ndbd process is initiated.

    The recommended directory hierarchy for MySQL Cluster includes /var/lib/mysql-cluster, under which a directory for the node's file system is created. The name of this subdirectory contains the node ID. For example, if the node ID is 2, this subdirectory is named ndb_2_fs.

  • BackupDataDir

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0path[see text]...IN

    This parameter specifies the directory in which backups are placed.

    Important

    The string '/BACKUP' is always appended to this value. For example, if you set the value of BackupDataDir to /var/lib/cluster-data, then all backups are stored under /var/lib/cluster-data/BACKUP. This also means that the effective default backup location is the directory named BACKUP under the location specified by the FileSystemPath parameter.

Data Memory, Index Memory, and String Memory

DataMemory and IndexMemory are [ndbd] parameters specifying the size of memory segments used to store the actual records and their indexes. In setting values for these, it is important to understand how DataMemory and IndexMemory are used, as they usually need to be updated to reflect actual usage by the cluster:

  • DataMemory

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0bytes80M1M - 1024GN

    This parameter defines the amount of space (in bytes) available for storing database records. The entire amount specified by this value is allocated in memory, so it is extremely important that the machine has sufficient physical memory to accommodate it.

    The memory allocated by DataMemory is used to store both the actual records and indexes. There is a 16-byte overhead on each record; an additional amount for each record is incurred because it is stored in a 32KB page with 128 byte page overhead (see below). There is also a small amount wasted per page due to the fact that each record is stored in only one page.

    For variable-size table attributes in MySQL 5.1, the data is stored on separate data pages, allocated from DataMemory. Variable-length records use a fixed-size part with an extra overhead of 4 bytes to reference the variable-size part. The variable-size part has 2 bytes overhead plus 2 bytes per attribute.

    Prior to MySQL Cluster NDB 7.0, the maximum record size was 8052 bytes; in MySQL Cluster NDB 7.0 and later, it is 14000 bytes.

    The memory space defined by DataMemory is also used to store ordered indexes, which use about 10 bytes per record. Each table row is represented in the ordered index. A common error among users is to assume that all indexes are stored in the memory allocated by IndexMemory, but this is not the case: Only primary key and unique hash indexes use this memory; ordered indexes use the memory allocated by DataMemory. However, creating a primary key or unique hash index also creates an ordered index on the same keys, unless you specify USING HASH in the index creation statement. This can be verified by running ndb_desc -d db_name table_name in the management client.

    MySQL Cluster can use a maximum of 512 MB for hash indexes per partition, which means in some cases it is possible to get Table is full errors in MySQL client applications even when ndb_mgm -e "ALL REPORT MEMORYUSAGE" shows significant free DataMemory. This can also pose a problem with data node restarts on nodes that are heavily loaded with data. You can force NDB to create extra partitions for MySQL Cluster tables and thus have more memory available for hash indexes by using the MAX_ROWS option for CREATE TABLE. In general, setting MAX_ROWS to twice the number of rows that you expect to store in the table should be sufficient. In MySQL Cluster 7.1.18 and later, you can also use the MinFreePct configuration parameter to help avoid problems with node restarts. (Bug #13436216)

    The memory space allocated by DataMemory consists of 32KB pages, which are allocated to table fragments. Each table is normally partitioned into the same number of fragments as there are data nodes in the cluster. Thus, for each node, there are the same number of fragments as are set in NoOfReplicas.

    In addition, due to the way in which new pages are allocated when the capacity of the current page is exhausted, there is an additional overhead of approximately 18.75%. When more DataMemory is required, more than one new page is allocated, according to the following formula:

    number of new pages = FLOOR(number of current pages × 0.1875) + 1
    

    For example, if 15 pages are currently allocated to a given table and an insert to this table requires additional storage space, the number of new pages allocated to the table is FLOOR(15 × 0.1875) + 1 = FLOOR(2.8125) + 1 = 2 + 1 = 3. Now 15 + 3 = 18 memory pages are allocated to the table. When the last of these 18 pages becomes full, FLOOR(18 × 0.1875) + 1 = FLOOR(3.3750) + 1 = 3 + 1 = 4 new pages are allocated, so the total number of pages allocated to the table is now 22.

    Note

    The 18.75% + 1 overhead is no longer required beginning with MySQL Cluster NDB 6.2.3 and MySQL Cluster NDB 6.3.0.

    Once a page has been allocated, it is currently not possible to return it to the pool of free pages, except by deleting the table. (This also means that DataMemory pages, once allocated to a given table, cannot be used by other tables.) Performing a node recovery also compresses the partition because all records are inserted into empty partitions from other live nodes.

    The DataMemory memory space also contains UNDO information: For each update, a copy of the unaltered record is allocated in the DataMemory. There is also a reference to each copy in the ordered table indexes. Unique hash indexes are updated only when the unique index columns are updated, in which case a new entry in the index table is inserted and the old entry is deleted upon commit. For this reason, it is also necessary to allocate enough memory to handle the largest transactions performed by applications using the cluster. In any case, performing a few large transactions holds no advantage over using many smaller ones, for the following reasons:

    • Large transactions are not any faster than smaller ones

    • Large transactions increase the number of operations that are lost and must be repeated in event of transaction failure

    • Large transactions use more memory

    The default value for DataMemory is 80MB; the minimum is 1MB. There is no maximum size, but in reality the maximum size has to be adapted so that the process does not start swapping when the limit is reached. This limit is determined by the amount of physical RAM available on the machine and by the amount of memory that the operating system may commit to any one process. 32-bit operating systems are generally limited to 2−4GB per process; 64-bit operating systems can use more. For large databases, it may be preferable to use a 64-bit operating system for this reason.

  • IndexMemory

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0bytes18M1M - 1TN

    This parameter controls the amount of storage used for hash indexes in MySQL Cluster. Hash indexes are always used for primary key indexes, unique indexes, and unique constraints. When defining a primary key or a unique index, two indexes are created, one of which is a hash index used for all tuple accesses as well as lock handling. This index is also used to enforce unique constraints.

    You can estimate the size of a hash index using this formula:

      size  = ( (fragments * 32K) + (rows * 18) )
              * replicas
              

    fragments is the number of fragments, replicas is the number of replicas (normally 2), and rows is the number of rows. If a table has one million rows, 8 fragments, and 2 replicas, the expected index memory usage is calculated as shown here:

              
      ((8 * 32K) + (1000000 * 18)) * 2 = ((8 * 32768) + (1000000 * 18)) * 2
      = (262144 + 18000000) * 2
      = 18262144 * 2 = 36524288 bytes = ~35MB
    

    The default value for IndexMemory is 18MB. The minimum is 1MB.

  • StringMemory

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0% or bytes00 - 4294967039 (0xFFFFFEFF)S
    MySQL 5.1.32% or bytes250 - 4294967039 (0xFFFFFEFF)S
    MySQL 5.1.6% or bytes50 - 4294967039 (0xFFFFFEFF)S
    NDB 7.2.1% or bytes250 - 4294967039 (0xFFFFFEFF)S

    This parameter determines how much memory is allocated for strings such as table names, and is specified in an [ndbd] or [ndbd default] section of the config.ini file. A value between 0 and 100 inclusive is interpreted as a percent of the maximum default value, which is calculated based on a number of factors including the number of tables, maximum table name size, maximum size of .FRM files, MaxNoOfTriggers, maximum column name size, and maximum default column value.

    A value greater than 100 is interpreted as a number of bytes.

    The default value is 25—that is, 25 percent of the default maximum. (Previously, prior to MySQL Cluster NDB 6.2.18, MySQL Cluster NDB 6.3.24, and MySQL Cluster NDB 7.0.5, the default value was 5; prior to MySQL 5.1.6, the default was 0.)

    Under most circumstances, the default value should be sufficient, but when you have a great many Cluster tables (1000 or more), it is possible to get Error 773 Out of string memory, please modify StringMemory config parameter: Permanent error: Schema error, in which case you should increase this value. 25 (25 percent) is not excessive, and should prevent this error from recurring in all but the most extreme conditions.

The following example illustrates how memory is used for a table. Consider this table definition:

CREATE TABLE example (
  a INT NOT NULL,
  b INT NOT NULL,
  c INT NOT NULL,
  PRIMARY KEY(a),
  UNIQUE(b)
) ENGINE=NDBCLUSTER;

For each record, there are 12 bytes of data plus 12 bytes overhead. Having no nullable columns saves 4 bytes of overhead. In addition, we have two ordered indexes on columns a and b consuming roughly 10 bytes each per record. There is a primary key hash index on the base table using roughly 29 bytes per record. The unique constraint is implemented by a separate table with b as primary key and a as a column. This other table consumes an additional 29 bytes of index memory per record in the example table as well 8 bytes of record data plus 12 bytes of overhead.

Thus, for one million records, we need 58MB for index memory to handle the hash indexes for the primary key and the unique constraint. We also need 64MB for the records of the base table and the unique index table, plus the two ordered index tables.

You can see that hash indexes takes up a fair amount of memory space; however, they provide very fast access to the data in return. They are also used in MySQL Cluster to handle uniqueness constraints.

The only partitioning algorithm is hashing and ordered indexes are local to each node. Thus, ordered indexes cannot be used to handle uniqueness constraints in the general case.

An important point for both IndexMemory and DataMemory is that the total database size is the sum of all data memory and all index memory for each node group. Each node group is used to store replicated information, so if there are four nodes with two replicas, there will be two node groups. Thus, the total data memory available is 2 × DataMemory for each data node.

It is highly recommended that DataMemory and IndexMemory be set to the same values for all nodes. Data distribution is even over all nodes in the cluster, so the maximum amount of space available for any node can be no greater than that of the smallest node in the cluster.

DataMemory and IndexMemory can be changed, but decreasing either of these can be risky; doing so can easily lead to a node or even an entire MySQL Cluster that is unable to restart due to there being insufficient memory space. Increasing these values should be acceptable, but it is recommended that such upgrades are performed in the same manner as a software upgrade, beginning with an update of the configuration file, and then restarting the management server followed by restarting each data node in turn.

MinFreePct.  Beginning with MySQL Cluster NDB 7.0.29 and MySQL Cluster NDB 7.1.18, a proportion (5% by default) of data node resources including DataMemory and IndexMemory is kept in reserve to insure that the data node does not exhaust its memory when performing a restart. This can be adjusted using the MinFreePct data node configuration parameter (default 5) introduced in the same versions of MySQL Cluster.

Effective VersionType/UnitsDefaultRange/ValuesRestart Type
NDB 7.0.29unsigned50 - 100N
NDB 7.1.18unsigned50 - 100N
NDB 7.2.3unsigned50 - 100N

Updates do not increase the amount of index memory used. Inserts take effect immediately; however, rows are not actually deleted until the transaction is committed.

Transaction parameters.  The next few [ndbd] parameters that we discuss are important because they affect the number of parallel transactions and the sizes of transactions that can be handled by the system. MaxNoOfConcurrentTransactions sets the number of parallel transactions possible in a node. MaxNoOfConcurrentOperations sets the number of records that can be in update phase or locked simultaneously.

Both of these parameters (especially MaxNoOfConcurrentOperations) are likely targets for users setting specific values and not using the default value. The default value is set for systems using small transactions, to ensure that these do not use excessive memory.

MaxDMLOperationsPerTransaction, added in MySQL Cluster NDB 7.0.26 and MySQL Cluster NDB 7.1.15, sets the maximum number of DML operations that can be performed in a given transaction.

  • MaxNoOfConcurrentTransactions

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer409632 - 4294967039 (0xFFFFFEFF)N

    Each cluster data node requires a transaction record for each active transaction in the cluster. The task of coordinating transactions is distributed among all of the data nodes. The total number of transaction records in the cluster is the number of transactions in any given node times the number of nodes in the cluster.

    Transaction records are allocated to individual MySQL servers. Each connection to an SQL node requires at least one transaction record, plus an additional transaction object per table accessed by that connection. This means that a reasonable minimum for this parameter is

    MaxNoOfConcurrentTransactions =
        (maximum number of tables accessed in any single transaction + 1)
        * number of cluster SQL nodes
    

    Suppose that there are 10 SQL nodes using the cluster. A single join involving 10 tables requires 11 transaction records; if there are 10 such joins in a transaction, then 10 * 11 = 110 transaction records are required for this transaction, per SQL node, or 110 * 10 = 1100 transaction records total. Each data node can be expected to handle TotalNoOfConcurrentTransactions / number of data nodes. For a MySQL Cluster having 4 data nodes, this would mean setting MaxNoOfConcurrentTransactions on each data node to 1100 / 4 = 275. In addition, you should provide for failure recovery by ensuring that a single node group can accommodate all concurrent transactions; in other words, that each data node's MaxNoOfConcurrentTransactions is sufficient to cover a number of transaction equal to TotalNoOfConcurrentTransactions / number of node groups. If this cluster has a single node group, then MaxNoOfConcurrentTransactions should be set to 1100 (the same as the total number of concurrent transactions for the entire cluster).

    In addition, each transaction involves at least one operation; for this reason, the value set for MaxNoOfConcurrentTransactions should always be no more than the value of MaxNoOfConcurrentOperations.

    This parameter must be set to the same value for all cluster data nodes. This is due to the fact that, when a data node fails, the oldest surviving node re-creates the transaction state of all transactions that were ongoing in the failed node.

    It is possible to change this value using a rolling restart, but the amount of traffic on the cluster must be such that no more transactions occur than the lower of the old and new levels while this is taking place.

    The default value is 4096.

  • MaxNoOfConcurrentOperations

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer32K32 - 4294967039 (0xFFFFFEFF)N

    It is a good idea to adjust the value of this parameter according to the size and number of transactions. When performing transactions which involve only a few operations and records, the default value for this parameter is usually sufficient. Performing large transactions involving many records usually requires that you increase its value.

    Records are kept for each transaction updating cluster data, both in the transaction coordinator and in the nodes where the actual updates are performed. These records contain state information needed to find UNDO records for rollback, lock queues, and other purposes.

    This parameter should be set to the number of records to be updated simultaneously in transactions, divided by the number of cluster data nodes. For example, in a cluster which has four data nodes and which is expected to handle one million concurrent updates using transactions, you should set this value to 1000000 / 4 = 250000. To help provide resiliency against failures, it is suggested that you set this parameter to a value that is high enough to permit an individual data node to handle the load for its node group. In other words, you should set the value equal to total number of concurrent operations / number of node groups. (In the case where there is a single node group, this is the same as the total number of concurrent operations for the entire cluster.)

    Because each transaction always involves at least one operation, the value of MaxNoOfConcurrentOperations should always be greater than or equal to the value of MaxNoOfConcurrentTransactions.

    Read queries which set locks also cause operation records to be created. Some extra space is allocated within individual nodes to accommodate cases where the distribution is not perfect over the nodes.

    When queries make use of the unique hash index, there are actually two operation records used per record in the transaction. The first record represents the read in the index table and the second handles the operation on the base table.

    The default value is 32768.

    This parameter actually handles two values that can be configured separately. The first of these specifies how many operation records are to be placed with the transaction coordinator. The second part specifies how many operation records are to be local to the database.

    A very large transaction performed on an eight-node cluster requires as many operation records in the transaction coordinator as there are reads, updates, and deletes involved in the transaction. However, the operation records of the are spread over all eight nodes. Thus, if it is necessary to configure the system for one very large transaction, it is a good idea to configure the two parts separately. MaxNoOfConcurrentOperations will always be used to calculate the number of operation records in the transaction coordinator portion of the node.

    It is also important to have an idea of the memory requirements for operation records. These consume about 1KB per record.

  • MaxNoOfLocalOperations

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integerUNDEFINED32 - 4294967039 (0xFFFFFEFF)N

    By default, this parameter is calculated as 1.1 × MaxNoOfConcurrentOperations. This fits systems with many simultaneous transactions, none of them being very large. If there is a need to handle one very large transaction at a time and there are many nodes, it is a good idea to override the default value by explicitly specifying this parameter.

  • MaxDMLOperationsPerTransaction

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.0.26operations (DML)429496729532 - 4294967295N
    NDB 7.1.15operations (DML)429496729532 - 4294967295N

    Added in MySQL Cluster NDB 7.0.26 and MySQL Cluster NDB 7.1.15, this parameter limits the size of a transaction. The transaction is aborted if it requires more than this many DML operations. The minimum number of operations per transaction is 32; however, you can set MaxDMLOperationsPerTransaction to 0 to disable any limitation on the number of DML operations per transaction. The maximum (and default) is 4294967295.

Transaction temporary storage.  The next set of [ndbd] parameters is used to determine temporary storage when executing a statement that is part of a Cluster transaction. All records are released when the statement is completed and the cluster is waiting for the commit or rollback.

The default values for these parameters are adequate for most situations. However, users with a need to support transactions involving large numbers of rows or operations may need to increase these values to enable better parallelism in the system, whereas users whose applications require relatively small transactions can decrease the values to save memory.

  • MaxNoOfConcurrentIndexOperations

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer8K0 - 4294967039 (0xFFFFFEFF)N

    For queries using a unique hash index, another temporary set of operation records is used during a query's execution phase. This parameter sets the size of that pool of records. Thus, this record is allocated only while executing a part of a query. As soon as this part has been executed, the record is released. The state needed to handle aborts and commits is handled by the normal operation records, where the pool size is set by the parameter MaxNoOfConcurrentOperations.

    The default value of this parameter is 8192. Only in rare cases of extremely high parallelism using unique hash indexes should it be necessary to increase this value. Using a smaller value is possible and can save memory if the DBA is certain that a high degree of parallelism is not required for the cluster.

  • MaxNoOfFiredTriggers

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer40000 - 4294967039 (0xFFFFFEFF)N

    The default value of MaxNoOfFiredTriggers is 4000, which is sufficient for most situations. In some cases it can even be decreased if the DBA feels certain the need for parallelism in the cluster is not high.

    A record is created when an operation is performed that affects a unique hash index. Inserting or deleting a record in a table with unique hash indexes or updating a column that is part of a unique hash index fires an insert or a delete in the index table. The resulting record is used to represent this index table operation while waiting for the original operation that fired it to complete. This operation is short-lived but can still require a large number of records in its pool for situations with many parallel write operations on a base table containing a set of unique hash indexes.

  • TransactionBufferMemory

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0bytes1M1K - 4294967039 (0xFFFFFEFF)N

    The memory affected by this parameter is used for tracking operations fired when updating index tables and reading unique indexes. This memory is used to store the key and column information for these operations. It is only very rarely that the value for this parameter needs to be altered from the default.

    The default value for TransactionBufferMemory is 1MB.

    Normal read and write operations use a similar buffer, whose usage is even more short-lived. The compile-time parameter ZATTRBUF_FILESIZE (found in ndb/src/kernel/blocks/Dbtc/Dbtc.hpp) set to 4000 × 128 bytes (500KB). A similar buffer for key information, ZDATABUF_FILESIZE (also in Dbtc.hpp) contains 4000 × 16 = 62.5KB of buffer space. Dbtc is the module that handles transaction coordination.

Scans and buffering.  There are additional [ndbd] parameters in the Dblqh module (in ndb/src/kernel/blocks/Dblqh/Dblqh.hpp) that affect reads and updates. These include ZATTRINBUF_FILESIZE, set by default to 10000 × 128 bytes (1250KB) and ZDATABUF_FILE_SIZE, set by default to 10000*16 bytes (roughly 156KB) of buffer space. To date, there have been neither any reports from users nor any results from our own extensive tests suggesting that either of these compile-time limits should be increased.

  • MaxNoOfConcurrentScans

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer2562 - 500N

    This parameter is used to control the number of parallel scans that can be performed in the cluster. Each transaction coordinator can handle the number of parallel scans defined for this parameter. Each scan query is performed by scanning all partitions in parallel. Each partition scan uses a scan record in the node where the partition is located, the number of records being the value of this parameter times the number of nodes. The cluster should be able to sustain MaxNoOfConcurrentScans scans concurrently from all nodes in the cluster.

    Scans are actually performed in two cases. The first of these cases occurs when no hash or ordered indexes exists to handle the query, in which case the query is executed by performing a full table scan. The second case is encountered when there is no hash index to support the query but there is an ordered index. Using the ordered index means executing a parallel range scan. The order is kept on the local partitions only, so it is necessary to perform the index scan on all partitions.

    The default value of MaxNoOfConcurrentScans is 256. The maximum value is 500.

  • MaxNoOfLocalScans

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer[see text]32 - 4294967039 (0xFFFFFEFF)N
    NDB 7.2.0integer[see text]32 - 4294967039 (0xFFFFFEFF)N

    Specifies the number of local scan records if many scans are not fully parallelized. In MySQL Cluster NDB 7.2.0 and later, when the number of local scan records is not provided, it is calculated as shown here:

    4 * MaxNoOfConcurrentScans * [# data nodes] + 2
    

    In MySQL Cluster NDB 7.1 and earlier, the default is calculated as the product of MaxNoOfConcurrentScans and the number of data nodes, plus 2. The minimum value is 32.

  • BatchSizePerLocalScan

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer641 - 992N
    NDB 7.2.1integer2561 - 992N

    This parameter is used to calculate the number of lock records used to handle concurrent scan operations.

    BatchSizePerLocalScan has a strong connection to the BatchSize defined in the SQL nodes.

  • LongMessageBuffer

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0bytes1M512K - 4294967039 (0xFFFFFEFF)N
    NDB 7.0.4bytes4M512K - 4294967039 (0xFFFFFEFF)N
    NDB 7.2.0bytes4M512K - 4294967039 (0xFFFFFEFF)N
    NDB 7.1.31bytes64M512K - 4294967039 (0xFFFFFEFF)N

    This is an internal buffer used for passing messages within individual nodes and between nodes. In MySQL Cluster NDB 6.4.3 and earlier, the default is 1MB; beginning with MySQL Cluster NDB 7.0.4, this increased to 4MB; the default increased to 64MB in MySQL Cluster NDB 7.1.31.

    This parameter seldom needs to be changed from the default. However, when replicating a MySQL Cluster using ndbmtd for the data nodes, you may need to increase this value to 8MB (or possibly more) to prevent data node instability, because ndbmtd uses much more of this resource than ndbd does. Beginning with MySQL Cluster NDB 7.0.13 and MySQL Cluster NDB 7.1.2, this should no longer be necessary when using ndbmtd with MySQL Cluster Replication (Bug #46914).

  • MaxParallelScansPerFragment

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.0.23bytes321 - 4294967039 (0xFFFFFEFF)N
    NDB 7.1.12bytes321 - 4294967039 (0xFFFFFEFF)N
    NDB 7.2.0bytes2561 - 4294967039 (0xFFFFFEFF)N

    Beginning with MySQL Cluster NDB 7.0.23 and MySQL Cluster NDB 7.1.12, it is possible to configure the maximum number of parallel scans (TUP scans and TUX scans) allowed before they begin queuing for serial handling. (Previously, the maximum number of parallel scans per fragment was fixed at 32.) You can increase this to take advantage of any unused CPU when performing large number of scans in parallel and improve their performance.

    Beginning with MySQL Cluster NDB 7.2.0, the default value for this parameter is increased from 32 to 256.

Memory Allocation

MaxAllocate

Effective VersionType/UnitsDefaultRange/ValuesRestart Type
NDB 6.1.19unsigned32M1M - 1GN
NDB 6.2.3unsigned32M1M - 1GN
MySQL 5.1.20unsigned32M1M - 1GN

This is the maximum size of the memory unit to use when allocating memory for tables. In cases where NDB gives Out of memory errors, but it is evident by examining the cluster logs or the output of DUMP 1000 that all available memory has not yet been used, you can increase the value of this parameter (or MaxNoOfTables, or both) to cause NDB to make sufficient memory available.

This parameter was introduced in MySQL 5.1.20, MySQL Cluster NDB 6.1.12 and MySQL Cluster NDB 6.2.3.

Hash Map Size

DefaultHashMapSize

Effective VersionType/UnitsDefaultRange/ValuesRestart Type
NDB 7.0.38LDM threads2400 - 3840N
NDB 7.1.27LDM threads2400 - 3840N

Beginning with MySQL Cluster NDB 7.0.38 and MySQL Cluster NDB 7.1.26, the size of the table hash maps used by NDB is configurable using this parameter; previously this value was hard-coded. DefaultHashMapSize can take any of three possible values (0, 240, 3840). These values and their effects are described in the following table:

ValueDescription / Effect
0Use the lowest value set, if any, for this parameter among all data nodes and API nodes in the cluster; if it is not set on any data or API node, use the default value.
240Original hash map size used by default in all MySQL Cluster NDB 7.1 and MySQL Cluster NDB 7.0 (and earlier) releases; effectively the only value prior to versions 7.0.38 and 7.1.26 (when this parameter was introduced).
3840Larger hash map size available beginning with MySQL Cluster NDB 7.0.38 and MySQL Cluster NDB 7.1.26

The primary intended use for this parameter is to facilitate upgrades and esecially downgrades between MySQL Cluster NDB 7.1 and later MySQL Cluster versions in which the larger hash map size (3840) is the default; by setting this parameter to 240 prior to performing an upgrade, you can cause the cluster to continue using the smaller size for table hash maps, in which case the tables remain compatible with earlier versions. DefaultHashMapSize can be set for individual data nodes, API nodes, or both, but setting it once only, in the [ndbd default] section of the config.ini file, is the recommended practice. You can also set this parameter to 0, in which case the default value is used.

After increasing this parameter, to have existing tables to take advantage of the new size, you can run ALTER TABLE ... REORGANIZE PARTITION on them, after which they can use the larger hash map size. This is in addition to performing a rolling restart, which makes the larger hash maps available to new tables, but does not enable existing tables to use them.

Decreasing this parameter online after any tables have been created or modified with DefaultHashMapSize equal to 3840 is not currently supported.

Logging and checkpointing.  The following [ndbd] parameters control log and checkpoint behavior.

  • NoOfFragmentLogFiles

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer83 - 4294967039 (0xFFFFFEFF)IN
    MySQL 5.1.0integer163 - 4294967039 (0xFFFFFEFF)IN

    This parameter sets the number of REDO log files for the node, and thus the amount of space allocated to REDO logging. Because the REDO log files are organized in a ring, it is extremely important that the first and last log files in the set (sometimes referred to as the head and tail log files, respectively) do not meet. When these approach one another too closely, the node begins aborting all transactions encompassing updates due to a lack of room for new log records.

    A REDO log record is not removed until the required number of local checkpoints has been completed since that log record was inserted (prior to MySQL Cluster NDB 6.3.8, this was 3 local checkpoints; in later versions of MySQL Cluster, only 2 local checkpoints are necessary). Checkpointing frequency is determined by its own set of configuration parameters discussed elsewhere in this chapter.

    How these parameters interact and proposals for how to configure them are discussed in Section 5.3.13, “Configuring MySQL Cluster Parameters for Local Checkpoints”.

    The default parameter value is 16, which by default means 16 sets of 4 16MB files for a total of 1024MB. Beginning with MySQL Cluster NDB 6.1.1, the size of the individual log files is configurable using the FragmentLogFileSize parameter. In scenarios requiring a great many updates, the value for NoOfFragmentLogFiles may need to be set as high as 300 or even higher to provide sufficient space for REDO logs.

    If the checkpointing is slow and there are so many writes to the database that the log files are full and the log tail cannot be cut without jeopardizing recovery, all updating transactions are aborted with internal error code 410 (Out of log file space temporarily). This condition prevails until a checkpoint has completed and the log tail can be moved forward.

    Important

    This parameter cannot be changed on the fly; you must restart the node using --initial. If you wish to change this value for all data nodes in a running cluster, you can do so using a rolling node restart (using --initial when starting each data node).

  • FragmentLogFileSize

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.1.11bytes16M4M - 1GIN

    Setting this parameter enables you to control directly the size of redo log files. This can be useful in situations when MySQL Cluster is operating under a high load and it is unable to close fragment log files quickly enough before attempting to open new ones (only 2 fragment log files can be open at one time); increasing the size of the fragment log files gives the cluster more time before having to open each new fragment log file. The default value for this parameter is 16M. FragmentLogFileSize was added in MySQL Cluster NDB 6.1.11.

    For more information about fragment log files, see the description for NoOfFragmentLogFiles.

  • InitFragmentLogFiles

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.19[see values]SPARSESPARSE, FULLIN

    By default, fragment log files are created sparsely when performing an initial start of a data node—that is, depending on the operating system and file system in use, not all bytes are necessarily written to disk. Beginning with MySQL Cluster NDB 6.3.19, it is possible to override this behavior and force all bytes to be written regardless of the platform and file system type being used by mean of this parameter.

    InitFragmentLogFiles takes one of two values:

    • SPARSE. Fragment log files are created sparsely. This is the default value.

    • FULL. Force all bytes of the fragment log file to be written to disk.

    Depending on your operating system and file system, setting InitFragmentLogFiles=FULL may help eliminate I/O errors on writes to the REDO log.

  • MaxNoOfOpenFiles

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer4020 - 4294967039 (0xFFFFFEFF)N
    MySQL 5.1.16unsigned020 - 4294967039 (0xFFFFFEFF)N

    This parameter sets a ceiling on how many internal threads to allocate for open files. Any situation requiring a change in this parameter should be reported as a bug.

    The default value is 0. (Prior to MySQL 5.1.16, the default was 40.) However, the minimum value to which this parameter can be set is 20.

  • InitialNoOfOpenFiles

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.9files2720 - 4294967039 (0xFFFFFEFF)N

    This parameter sets the initial number of internal threads to allocate for open files.

    The default value is 27.

  • MaxNoOfSavedMessages

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer250 - 4294967039 (0xFFFFFEFF)N

    This parameter sets the maximum number of errors written in the error log as well as the maximum number of trace files that are kept before overwriting the existing ones. Trace files are generated when, for whatever reason, the node crashes.

    The default is 25, which sets these maximums to 25 error messages and 25 trace files.

  • MaxLCPStartDelay

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.23seconds00 - 600N
    NDB 6.4.3seconds00 - 600N

    In parallel data node recovery (supported in MySQL Cluster NDB 6.3.8 and later), only table data is actually copied and synchronized in parallel; synchronization of metadata such as dictionary and checkpoint information is done in a serial fashion. In addition, recovery of dictionary and checkpoint information cannot be executed in parallel with performing of local checkpoints. This means that, when starting or restarting many data nodes concurrently, data nodes may be forced to wait while a local checkpoint is performed, which can result in longer node recovery times.

    Beginning with MySQL Cluster NDB 6.3.23 and MySQL Cluster NDB 6.4.3, it is possible to force a delay in the local checkpoint to permit more (and possibly all) data nodes to complete metadata synchronization; once each data node's metadata synchronization is complete, all of the data nodes can recover table data in parallel, even while the local checkpoint is being executed.

    To force such a delay, you can set MaxLCPStartDelay, which determines the number of seconds the cluster can wait to begin a local checkpoint while data nodes continue to synchronize metadata. This parameter should be set in the [ndbd default] section of the config.ini file, so that it is the same for all data nodes. The maximum value is 600; the default is 0.

  • LcpScanProgressTimeout

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.0.40second600 - 4294967039 (0xFFFFFEFF)N
    NDB 7.1.29second600 - 4294967039 (0xFFFFFEFF)N

    A local checkpoint fragment scan watchdog checks periodically for no progress in each fragment scan performed as part of a local checkpoint, and shuts down the node if there is no progress after a given amount of time has elapsed. Prior to MySQL Cluster NDB 7.0.39 and MySQL Cluster NDB 7.1.29, this interval is always 60 seconds (Bug #16630410). In MySQL Cluster NDB 7.0.39, MySQL Cluster NDB 7.1.29, and later this interval can be set using the LcpScanProgressTimeout data node configuration parameter, which sets the maximum time for which the local checkpoint can be stalled before the LCP fragment scan watchdog shuts down the node.

    The default value is 60 seconds (providing compatibility with previous releases). Setting this parameter to 0 disables the LCP fragment scan watchdog altogether.

Metadata objects.  The next set of [ndbd] parameters defines pool sizes for metadata objects, used to define the maximum number of attributes, tables, indexes, and trigger objects used by indexes, events, and replication between clusters. Note that these act merely as suggestions to the cluster, and any that are not specified revert to the default values shown.

  • MaxNoOfAttributes

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer100032 - 4294967039 (0xFFFFFEFF)N

    This parameter sets a suggested maximum number of attributes that can be defined in the cluster; like MaxNoOfTables, it is not intended to function as a hard upper limit.

    Prior to MySQL Cluster NDB 6.3.45, MySQL Cluster NDB 7.0.26, and MySQL Cluster NDB 7.1.15, this parameter was sometimes treated as a hard limit for certain operations. This caused problems with MySQL Cluster Replication, when it was possible to create more tables than could be replicated, and sometimes led to confusion when it was possible (or not possible, depending on the circumstances) to create more than MaxNoOfAttributes attributes. (Bug #61684)

    The default value is 1000, with the minimum possible value being 32. The maximum is 4294967039. Each attribute consumes around 200 bytes of storage per node due to the fact that all metadata is fully replicated on the servers.

    When setting MaxNoOfAttributes, it is important to prepare in advance for any ALTER TABLE statements that you might want to perform in the future. This is due to the fact, during the execution of ALTER TABLE on a Cluster table, 3 times the number of attributes as in the original table are used, and a good practice is to permit double this amount. For example, if the MySQL Cluster table having the greatest number of attributes (greatest_number_of_attributes) has 100 attributes, a good starting point for the value of MaxNoOfAttributes would be 6 * greatest_number_of_attributes = 600.

    You should also estimate the average number of attributes per table and multiply this by MaxNoOfTables. If this value is larger than the value obtained in the previous paragraph, you should use the larger value instead.

    Assuming that you can create all desired tables without any problems, you should also verify that this number is sufficient by trying an actual ALTER TABLE after configuring the parameter. If this is not successful, increase MaxNoOfAttributes by another multiple of MaxNoOfTables and test it again.

  • MaxNoOfTables

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer1288 - 20320N

    A table object is allocated for each table and for each unique hash index in the cluster. This parameter sets a suggested maximum number of table objects for the cluster as a whole; like MaxNoOfAttributes, it is not intended to function as a hard upper limit.

    Prior to MySQL Cluster NDB 6.3.45, MySQL Cluster NDB 7.0.26, and MySQL Cluster NDB 7.1.15, this parameter was sometimes treated as a hard limit for certain operations. This caused problems with MySQL Cluster Replication, when it was possible to create more tables than could be replicated, and sometimes led to confusion when it was possible (or not possible, depending on the circumstances) to create more than MaxNoOfTables tables.

    For each attribute that has a BLOB data type an extra table is used to store most of the BLOB data. These tables also must be taken into account when defining the total number of tables.

    The default value of this parameter is 128. The minimum is 8 and the maximum is 20320. Each table object consumes approximately 20KB per node.

    Note

    The sum of MaxNoOfTables, MaxNoOfOrderedIndexes, and MaxNoOfUniqueHashIndexes must not exceed 232 − 2 (4294967294).

  • MaxNoOfOrderedIndexes

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer1280 - 4294967039 (0xFFFFFEFF)N

    For each ordered index in the cluster, an object is allocated describing what is being indexed and its storage segments. By default, each index so defined also defines an ordered index. Each unique index and primary key has both an ordered index and a hash index. MaxNoOfOrderedIndexes sets the total number of ordered indexes that can be in use in the system at any one time.

    The default value of this parameter is 128. Each index object consumes approximately 10KB of data per node.

    Note

    The sum of MaxNoOfTables, MaxNoOfOrderedIndexes, and MaxNoOfUniqueHashIndexes must not exceed 232 − 2 (4294967294).

  • MaxNoOfUniqueHashIndexes

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer640 - 4294967039 (0xFFFFFEFF)N

    For each unique index that is not a primary key, a special table is allocated that maps the unique key to the primary key of the indexed table. By default, an ordered index is also defined for each unique index. To prevent this, you must specify the USING HASH option when defining the unique index.

    The default value is 64. Each index consumes approximately 15KB per node.

    Note

    The sum of MaxNoOfTables, MaxNoOfOrderedIndexes, and MaxNoOfUniqueHashIndexes must not exceed 232 − 2 (4294967294).

  • MaxNoOfTriggers

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer7680 - 4294967039 (0xFFFFFEFF)N

    Internal update, insert, and delete triggers are allocated for each unique hash index. (This means that three triggers are created for each unique hash index.) However, an ordered index requires only a single trigger object. Backups also use three trigger objects for each normal table in the cluster.

    Replication between clusters also makes use of internal triggers.

    This parameter sets the maximum number of trigger objects in the cluster.

    The default value is 768.

  • MaxNoOfIndexes

    This parameter is deprecated. You should use MaxNoOfOrderedIndexes and MaxNoOfUniqueHashIndexes instead.

    This parameter is used only by unique hash indexes. There needs to be one record in this pool for each unique hash index defined in the cluster.

    The default value of this parameter is 128.

  • MaxNoOfSubscriptions

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.2.10unsigned00 - 4294967039 (0xFFFFFEFF)N
    NDB 6.3.7unsigned00 - 4294967039 (0xFFFFFEFF)N

    Each NDB table in a MySQL Cluster requires a subscription in the NDB kernel. For some NDB API applications, it may be necessary or desirable to change this parameter, which became available in MySQL Cluster NDB 6.2.10 and MySQL Cluster NDB 6.3.7. However, for normal usage with MySQL servers acting as SQL nodes, there is not any need to do so.

    The default value for MaxNoOfSubscriptions is 0, which is treated as equal to MaxNoOfTables. Each subscription consumes 108 bytes.

  • MaxNoOfSubscribers

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.2.10unsigned00 - 4294967039 (0xFFFFFEFF)N
    NDB 6.3.7unsigned00 - 4294967039 (0xFFFFFEFF)N

    This parameter, added in MySQL Cluster NDB 6.2.10 and MySQL Cluster NDB 6.3.7, is of interest only when using MySQL Cluster Replication. The default value is 0, which is treated as 2 * MaxNoOfTables; that is, there is one subscription per NDB table for each of two MySQL servers (one acting as the replication master and the other as the slave). Each subscriber uses 16 bytes of memory.

    When using circular replication, multi-master replication, and other replication setups involving more than 2 MySQL servers, you should increase this parameter to the number of mysqld processes included in replication (this is often, but not always, the same as the number of clusters). For example, if you have a circular replication setup using three MySQL Clusters, with one mysqld attached to each cluster, and each of these mysqld processes acts as a master and as a slave, you should set MaxNoOfSubscribers equal to 3 * MaxNoOfTables.

    For more information, see Chapter 8, MySQL Cluster Replication.

  • MaxNoOfConcurrentSubOperations

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.2.10unsigned2560 - 4294967039 (0xFFFFFEFF)N
    NDB 6.3.7unsigned2560 - 4294967039 (0xFFFFFEFF)N

    This parameter sets a ceiling on the number of operations that can be performed by all API nodes in the cluster at one time. The default value (256) is sufficient for normal operations, and might need to be adjusted only in scenarios where there are a great many API nodes each performing a high volume of operations concurrently.

    This parameter was added in MySQL Cluster NDB 6.2.10 and MySQL Cluster NDB 6.3.7.

Boolean parameters.  The behavior of data nodes is also affected by a set of [ndbd] parameters taking on boolean values. These parameters can each be specified as TRUE by setting them equal to 1 or Y, and as FALSE by setting them equal to 0 or N.

  • LateAlloc

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.4.0numeric10 - 1N

    Allocate memory for this data node after a connection to the management server has been established. Enabled by default.

    Added in MySQL Cluster NDB 6.4.0.

  • LockPagesInMainMemory

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0numeric00 - 2N
    MySQL 5.1.0true|false (1|0)00 - 1N
    MySQL 5.1.15numeric00 - 2N

    For a number of operating systems, including Solaris and Linux, it is possible to lock a process into memory and so avoid any swapping to disk. This can be used to help guarantee the cluster's real-time characteristics.

    Beginning with MySQL 5.1.15 and MySQL Cluster NDB 6.1.1, this parameter takes one of the integer values 0, 1, or 2, which act as follows:

    • 0: Disables locking. This is the default value.

    • 1: Performs the lock after allocating memory for the process.

    • 2: Performs the lock before memory for the process is allocated.

    Previously, this parameter was a Boolean. 0 or false was the default setting, and disabled locking. 1 or true enabled locking of the process after its memory was allocated.

    Important

    Beginning with MySQL 5.1.15 and MySQL Cluster NDB 6.1.1, it is no longer possible to use true or false for the value of this parameter; when upgrading from a previous version, you must change the value to 0, 1, or 2.

    Prior to MySQL Cluster NDB 6.3.31 and MySQL Cluster NDB 7.0.11, setting this parameter did not cause the stated memory to be allocated when the node was started, but rather only when the memory was used by the data node process for other reasons. (Bug #37430)

    Note

    If the operating system is not configured to permit unprivileged users to lock pages, then the data node process making use of this parameter may have to be run as system root. (LockPagesInMainMemory uses the mlockall function. From Linux kernel 2.6.9, unprivileged users can lock memory as limited by max locked memory. For more information, see ulimit -l and http://linux.die.net/man/2/mlock).

    Important

    Beginning with glibc 2.10, glibc uses per-thread arenas to reduce lock contention on a shared pool, which consumes real memory. In general, a data node process does not need per-thread arenas, since it does not perform any memory allocation after startup. (This difference in allocators does not appear to affect performance significantly.)

    The glibc behavior is intended to be configurable via the MALLOC_ARENA_MAX environment variable, but a bug in this mechanism prior to glibc 2.16 meant that this variable could not be set to less than 8, so that the wasted memory could not be reclaimed. (Bug #15907219; see also http://sourceware.org/bugzilla/show_bug.cgi?id=13137 for more information concerning this issue.)

    One possible workaround for this problem is to use the LD_PRELOAD environment variable to preload a jemalloc memory allocation library to take the place of that supplied with glibc.

  • StopOnError

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0boolean10, 1N

    This parameter specifies whether a data node process should exit or perform an automatic restart when an error condition is encountered.

    This parameter's default value is 1; this means that, by default, an error causes the data node process to halt.

    Users of MySQL Cluster Manager should note that, when StopOnError equals 1, this prevents the MySQL Cluster Manager agent from restarting any data nodes after it has performed its own restart and recovery. See Starting and Stopping the Agent on Linux, for more information.

  • CrashOnCorruptedTuple

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.0.28, 5.1.56-ndb-7.1.17booleanfalsetrue, falseS
    NDB 7.2.1booleantruetrue, falseS

    This parameter was introduced in MySQL Cluster NDB 7.0.28 and MySQL Cluster NDB 7.1.17. When enabled, it forces a data node to shut down whenever it encounters a corrupted tuple. By default, it is disabled.

  • Diskless

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0true|false (1|0)falsetrue, falseIS

    It is possible to specify MySQL Cluster tables as diskless, meaning that tables are not checkpointed to disk and that no logging occurs. Such tables exist only in main memory. A consequence of using diskless tables is that neither the tables nor the records in those tables survive a crash. However, when operating in diskless mode, it is possible to run ndbd on a diskless computer.

    Important

    This feature causes the entire cluster to operate in diskless mode.

    When this feature is enabled, Cluster online backup is disabled. In addition, a partial start of the cluster is not possible.

    Diskless is disabled by default.

  • ODirect

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.1.11booleanfalsetrue, falseN
    NDB 6.2.3booleanfalsetrue, falseN
    NDB 6.3.0booleanfalsetrue, falseN

    Enabling this parameter causes NDB to attempt using O_DIRECT writes for LCP, backups, and redo logs, often lowering kswapd and CPU usage. When using MySQL Cluster on Linux, enable ODirect if you are using a 2.6 or later kernel.

    This parameter was added in MySQL 5.1.20, MySQL Cluster NDB 6.1.11, MySQL Cluster NDB 6.2.3, and MySQL Cluster NDB 6.3.0.

    ODirect is disabled by default.

  • RestartOnErrorInsert

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0error code20 - 4N

    This feature is accessible only when building the debug version where it is possible to insert errors in the execution of individual blocks of code as part of testing.

    This feature is disabled by default.

  • CompressedBackup

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.7booleanfalsetrue, falseN

    Setting this parameter to 1 causes backup files to be compressed. The compression used is equivalent to gzip --fast, and can save 50% or more of the space required on the data node to store uncompressed backup files. Compressed backups can be enabled for individual data nodes, or for all data nodes (by setting this parameter in the [ndbd default] section of the config.ini file).

    Important

    You cannot restore a compressed backup to a cluster running a MySQL version that does not support this feature.

    The default value is 0 (disabled).

    This parameter was introduced in MySQL Cluster NDB 6.3.7.

  • CompressedLCP

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.7booleanfalsetrue, falseN

    Setting this parameter to 1 causes local checkpoint files to be compressed. The compression used is equivalent to gzip --fast, and can save 50% or more of the space required on the data node to store uncompressed checkpoint files. Compressed LCPs can be enabled for individual data nodes, or for all data nodes (by setting this parameter in the [ndbd default] section of the config.ini file).

    Important

    You cannot restore a compressed local checkpoint to a cluster running a MySQL version that does not support this feature.

    The default value is 0 (disabled).

    This parameter was introduced in MySQL Cluster NDB 6.3.7.

Controlling Timeouts, Intervals, and Disk Paging

There are a number of [ndbd] parameters specifying timeouts and intervals between various actions in Cluster data nodes. Most of the timeout values are specified in milliseconds. Any exceptions to this are mentioned where applicable.

  • TimeBetweenWatchDogCheck

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0milliseconds600070 - 4294967039 (0xFFFFFEFF)N

    To prevent the main thread from getting stuck in an endless loop at some point, a watchdog thread checks the main thread. This parameter specifies the number of milliseconds between checks. If the process remains in the same state after three checks, the watchdog thread terminates it.

    This parameter can easily be changed for purposes of experimentation or to adapt to local conditions. It can be specified on a per-node basis although there seems to be little reason for doing so.

    The default timeout is 6000 milliseconds (6 seconds).

  • TimeBetweenWatchDogCheckInitial

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.20milliseconds600070 - 4294967039 (0xFFFFFEFF)N

    This is similar to the TimeBetweenWatchDogCheck parameter, except that TimeBetweenWatchDogCheckInitial controls the amount of time that passes between execution checks inside a database node in the early start phases during which memory is allocated.

    The default timeout is 6000 milliseconds (6 seconds).

    This parameter was added in MySQL 5.1.20.

  • StartPartialTimeout

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0milliseconds300000 - 4294967039 (0xFFFFFEFF)N

    This parameter specifies how long the Cluster waits for all data nodes to come up before the cluster initialization routine is invoked. This timeout is used to avoid a partial Cluster startup whenever possible.

    This parameter is overridden when performing an initial start or initial restart of the cluster.

    The default value is 30000 milliseconds (30 seconds). 0 disables the timeout, in which case the cluster may start only if all nodes are available.

  • StartPartitionedTimeout

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0milliseconds600000 - 4294967039 (0xFFFFFEFF)N

    If the cluster is ready to start after waiting for StartPartialTimeout milliseconds but is still possibly in a partitioned state, the cluster waits until this timeout has also passed. If StartPartitionedTimeout is set to 0, the cluster waits indefinitely.

    This parameter is overridden when performing an initial start or initial restart of the cluster.

    The default timeout is 60000 milliseconds (60 seconds).

  • StartFailureTimeout

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0milliseconds00 - 4294967039 (0xFFFFFEFF)N

    If a data node has not completed its startup sequence within the time specified by this parameter, the node startup fails. Setting this parameter to 0 (the default value) means that no data node timeout is applied.

    For nonzero values, this parameter is measured in milliseconds. For data nodes containing extremely large amounts of data, this parameter should be increased. For example, in the case of a data node containing several gigabytes of data, a period as long as 10−15 minutes (that is, 600000 to 1000000 milliseconds) might be required to perform a node restart.

  • StartNoNodeGroupTimeout

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.0.24milliseconds150000 - 4294967039 (0xFFFFFEFF)N

    When a data node is configured with Nodegroup = 65536, is regarded as not being assigned to any node group. When that is done, the cluster waits StartNoNodegroupTimeout milliseconds, then treats such nodes as though they had been added to the list passed to the --nowait-nodes option, and starts. The default value is 15000 (that is, the management server waits 15 seconds). Setting this parameter equal to 0 means that the cluster waits indefinitely.

    StartNoNodegroupTimeout must be the same for all data nodes in the cluster; for this reason, you should always set it in the [ndbd default] section of the config.ini file, rather than for individual data nodes.

    This parameter was added in MySQL Cluster NDB 7.0.24 and MySQL Cluster NDB 7.1.13. See Section 7.13, “Adding MySQL Cluster Data Nodes Online”, for more information.

  • HeartbeatIntervalDbDb

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0milliseconds150010 - 4294967039 (0xFFFFFEFF)N
    NDB 7.2.0milliseconds500010 - 4294967039 (0xFFFFFEFF)N

    One of the primary methods of discovering failed nodes is by the use of heartbeats. This parameter states how often heartbeat signals are sent and how often to expect to receive them. After missing three heartbeat intervals in a row, the node is declared dead. Thus, the maximum time for discovering a failure through the heartbeat mechanism is four times the heartbeat interval.

    In MySQL Cluster NDB 7.2.0 and later, the default heartbeat interval is 5000 milliseconds (5 seconds). Previously, the default was 1500 milliseconds (1.5 seconds). This parameter must not be changed drastically and should not vary widely between nodes. If one node uses 5000 milliseconds and the node watching it uses 1000 milliseconds, obviously the node will be declared dead very quickly. This parameter can be changed during an online software upgrade, but only in small increments.

    See also Network communication and latency.

  • HeartbeatIntervalDbApi

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0milliseconds1500100 - 4294967039 (0xFFFFFEFF)N

    Each data node sends heartbeat signals to each MySQL server (SQL node) to ensure that it remains in contact. If a MySQL server fails to send a heartbeat in time it is declared dead, in which case all ongoing transactions are completed and all resources released. The SQL node cannot reconnect until all activities initiated by the previous MySQL instance have been completed. The three-heartbeat criteria for this determination are the same as described for HeartbeatIntervalDbDb.

    The default interval is 1500 milliseconds (1.5 seconds). This interval can vary between individual data nodes because each data node watches the MySQL servers connected to it, independently of all other data nodes.

    For more information, see Network communication and latency.

  • HeartbeatOrder

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.35numeric00 - 65535S
    NDB 7.0.16numeric00 - 65535S
    NDB 7.1.5numeric00 - 65535S

    Data nodes send heartbeats to one another in a circular fashion whereby each data node monitors the previous one. If a heartbeat is not detected by a given data node, this node declares the previous data node in the circle dead (that is, no longer accessible by the cluster). The determination that a data node is dead is done globally; in other words; once a data node is declared dead, it is regarded as such by all nodes in the cluster.

    It is possible for heartbeats between data nodes residing on different hosts to be too slow compared to heartbeats between other pairs of nodes (for example, due to a very low heartbeat interval or temporary connection problem), such that a data node is declared dead, even though the node can still function as part of the cluster.

    In this type of situation, it may be that the order in which heartbeats are transmitted between data nodes makes a difference as to whether or not a particular data node is declared dead. If this declaration occurs unnecessarily, this can in turn lead to the unnecessary loss of a node group and as thus to a failure of the cluster.

    Consider a setup where there are 4 data nodes A, B, C, and D running on 2 host computers host1 and host2, and that these data nodes make up 2 node groups, as shown in the following table:

    Node Group

    Nodes Running on host1

    Nodes Running on host2

    Node Group 0:

    Node A

    Node B

    Node Group 1:

    Node C

    Node D

    Suppose the heartbeats are transmitted in the order A->B->C->D->A. In this case, the loss of the heartbeat between the hosts causes node B to declare node A dead and node C to declare node B dead. This results in loss of Node Group 0, and so the cluster fails. On the other hand, if the order of transmission is A->B->D->C->A (and all other conditions remain as previously stated), the loss of the heartbeat causes nodes A and D to be declared dead; in this case, each node group has one surviving node, and the cluster survives.

    Priot to MySQL Cluster NDB 6.3.35, MySQL Cluster NDB 7.0.16, and MySQL Cluster NDB 7.1.5, the order of heartbeat transmission between data nodes was always automatically determined by NDB. However, beginning with these versions, the HeartbeatOrder configuration parameter makes the order of heartbeat transmission user-configurable.

    The default value for HeartbeatOrder is zero; allowing the default value to be used on all data nodes causes the order of heartbeat transmission to be determined by NDB. If this parameter is used, it must be set to a nonzero value (maximum 65535) for every data node in the cluster, and this value must be unique for each data node; this causes the heartbeat transmission to proceed from data node to data node in the order of their HeartbeatOrder values from lowest to highest (and then directly from the data node having the highest HeartbeatOrder to the data node having the lowest value, to complete the circle). The values need not be consecutive; for example, to force the heartbeat transmission order A->B->D->C->A in the scenario outlined previously, you could set the HeartbeatOrder values as shown here:

    NodeHeartbeatOrder
    A10
    B20
    C30
    D25

    To use this parameter to change the heartbeat transmission order in a running MySQL Cluster, you must first set HeartbeatOrder for each data node in the cluster in the global configuration (config.ini) file (or files). To cause the change to take effect, you must perform either of the following:

    • A complete shutdown and restart of the entire cluster.

    • 2 rolling restarts of the cluster in succession. All nodes must be restarted in the same order in both rolling restarts.

    You can use DUMP 908 to observe the effect of this parameter in the data node logs.

  • ConnectCheckIntervalDelay

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.1.13milliseconds15000 - 4294967039 (0xFFFFFEFF)N
    NDB 7.2.1milliseconds00 - 4294967039 (0xFFFFFEFF)N

    This parameter enables connection checking between data nodes. A data node that fails to respond within an interval of ConnectCheckIntervalDelay milliseconds is considered suspect, and is considered dead after two such intervals.

  • TimeBetweenLocalCheckpoints

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0number of 4-byte words, as a base-2 logarithm200 - 31N

    This parameter is an exception in that it does not specify a time to wait before starting a new local checkpoint; rather, it is used to ensure that local checkpoints are not performed in a cluster where relatively few updates are taking place. In most clusters with high update rates, it is likely that a new local checkpoint is started immediately after the previous one has been completed.

    The size of all write operations executed since the start of the previous local checkpoints is added. This parameter is also exceptional in that it is specified as the base-2 logarithm of the number of 4-byte words, so that the default value 20 means 4MB (4 × 220) of write operations, 21 would mean 8MB, and so on up to a maximum value of 31, which equates to 8GB of write operations.

    All the write operations in the cluster are added together. Setting TimeBetweenLocalCheckpoints to 6 or less means that local checkpoints will be executed continuously without pause, independent of the cluster's workload.

  • TimeBetweenGlobalCheckpoints

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0milliseconds200010 - 32000N
    NDB 6.2.0milliseconds200020 - 32000N

    When a transaction is committed, it is committed in main memory in all nodes on which the data is mirrored. However, transaction log records are not flushed to disk as part of the commit. The reasoning behind this behavior is that having the transaction safely committed on at least two autonomous host machines should meet reasonable standards for durability.

    It is also important to ensure that even the worst of cases—a complete crash of the cluster—is handled properly. To guarantee that this happens, all transactions taking place within a given interval are put into a global checkpoint, which can be thought of as a set of committed transactions that has been flushed to disk. In other words, as part of the commit process, a transaction is placed in a global checkpoint group. Later, this group's log records are flushed to disk, and then the entire group of transactions is safely committed to disk on all computers in the cluster.

    This parameter defines the interval between global checkpoints. The default is 2000 milliseconds.

  • TimeBetweenEpochs

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.2.5milliseconds1000 - 32000N

    This parameter defines the interval between synchronization epochs for MySQL Cluster Replication. The default value is 100 milliseconds.

    TimeBetweenEpochs is part of the implementation of micro-GCPs, which can be used to improve the performance of MySQL Cluster Replication. This parameter was introduced in MySQL Cluster NDB 6.2.5 and MySQL Cluster NDB 6.3.2.

  • TimeBetweenEpochsTimeout

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.22milliseconds40000 - 32000N
    MySQL 5.1.51milliseconds00 - 256000N

    This parameter defines a timeout for synchronization epochs for MySQL Cluster Replication. If a node fails to participate in a global checkpoint within the time determined by this parameter, the node is shut down. In MySQL Cluster NDB 7.2.0 and later, the default value is 0; in other words, the timeout is disabled. This represents a change from previous versions of MySQL Cluster, in which the default value was 4000 milliseconds (4 seconds).

    TimeBetweenEpochsTimeout is part of the implementation of micro-GCPs, which can be used to improve the performance of MySQL Cluster Replication. This parameter was introduced in MySQL Cluster NDB 6.2.7 and MySQL Cluster NDB 6.3.4.

    The following changes regarding this parameter were made in MySQL Cluster NDB 7.0.21 and MySQL Cluster NDB 7.1.10:

    • The maximum possible value for this parameter was increased from 32000 milliseconds to 256000 milliseconds.

    • Setting this parameter to zero now has the effect of disabling GCP stops caused by save timeouts, commit timeouts, or both.

    • The current value of this parameter and a warning are now written to the cluster log whenever a GCP save takes longer than 1 minute or a GCP save takes longer than 10 seconds.

  • MaxBufferedEpochs

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.2.14epochs1000 - 100000N

    The number of unprocessed epochs by which a subscribing node can lag behind. Exceeding this number causes a lagging subscriber to be disconnected.

    The default value of 100 is sufficient for most normal operations. If a subscribing node does lag enough to cause disconnections, it is usually due to network or scheduling issues with regard to processes or threads. (In rare circumstances, the problem may be due to a bug in the NDB client.) It may be desirable to set the value lower than the default when epochs are longer.

    Disconnection prevents client issues from affecting the data node service, running out of memory to buffer data, and eventually shutting down. Instead, only the client is affected as a result of the disconnect (by, for example gap events in the binary log), forcing the client to reconnect or restart the process.

  • MaxBufferedEpochBytes

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.52bytes2621440026214400 (0x01900000) - 4294967039 (0xFFFFFEFF)N
    NDB 7.0.38bytes2621440026214400 (0x01900000) - 4294967039 (0xFFFFFEFF)N
    NDB 7.1.27bytes2621440026214400 (0x01900000) - 4294967039 (0xFFFFFEFF)N

    The total number of bytes allocated for buffering epochs by this node.

    This parameter was introduced in MySQL Cluster NDB 6.3.52, MySQL Cluster NDB 7.0.38, and MySQL Cluster NDB 7.1.27. (Bug #16203623)

  • TimeBetweenInactiveTransactionAbortCheck

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0milliseconds10001000 - 4294967039 (0xFFFFFEFF)N

    Timeout handling is performed by checking a timer on each transaction once for every interval specified by this parameter. Thus, if this parameter is set to 1000 milliseconds, every transaction will be checked for timing out once per second.

    The default value is 1000 milliseconds (1 second).

  • TransactionInactiveTimeout

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0milliseconds[see text]0 - 4294967039 (0xFFFFFEFF)N

    This parameter states the maximum time that is permitted to lapse between operations in the same transaction before the transaction is aborted.

    The default for this parameter is 4G (also the maximum). For a real-time database that needs to ensure that no transaction keeps locks for too long, this parameter should be set to a relatively small value. The unit is milliseconds.

  • TransactionDeadlockDetectionTimeout

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0milliseconds120050 - 4294967039 (0xFFFFFEFF)N

    When a node executes a query involving a transaction, the node waits for the other nodes in the cluster to respond before continuing. A failure to respond can occur for any of the following reasons:

    • The node is dead

    • The operation has entered a lock queue

    • The node requested to perform the action could be heavily overloaded.

    This timeout parameter states how long the transaction coordinator waits for query execution by another node before aborting the transaction, and is important for both node failure handling and deadlock detection. In MySQL 5.1.10 and earlier versions, setting it too high could cause undesirable behavior in situations involving deadlocks and node failure. Beginning with MySQL 5.1.11, active transactions occurring during node failures are actively aborted by the MySQL Cluster Transaction Coordinator, and so high settings are no longer an issue with this parameter.

    The default timeout value is 1200 milliseconds (1.2 seconds).

    Prior to MySQL Cluster NDB versions 6.2.18, 6.3.24, and 7.0.5, the effective minimum for this parameter was 100 milliseconds. (Bug #44099) Beginning with these versions, the actual minimum is 50 milliseconds.

  • DiskSyncSize

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.12bytes4M32K - 4294967039 (0xFFFFFEFF)N

    This is the maximum number of bytes to store before flushing data to a local checkpoint file. This is done to prevent write buffering, which can impede performance significantly. This parameter is not intended to take the place of TimeBetweenLocalCheckpoints.

    Note

    When ODirect is enabled, it is not necessary to set DiskSyncSize; in fact, in such cases its value is simply ignored.

    The default value is 4M (4 megabytes).

    This parameter was added in MySQL 5.1.12.

  • DiskCheckpointSpeed

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.12bytes10M1M - 4294967039 (0xFFFFFEFF)N

    The amount of data,in bytes per second, that is sent to disk during a local checkpoint. This allocation is shared by DML operations and backups (but not backup logging), which means that backups started during times of intensive DML may be impaired by flooding of the redo log buffer and may fail altogether if the contention is sufficiently severe.

    The default value is 10M (10 megabytes per second).

    This parameter was added in MySQL 5.1.12.

  • DiskCheckpointSpeedInRestart

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.12bytes100M1M - 4294967039 (0xFFFFFEFF)N

    The amount of data,in bytes per second, that is sent to disk during a local checkpoint as part of a restart operation.

    The default value is 100M (100 megabytes per second).

    This parameter was added in MySQL 5.1.12.

  • NoOfDiskPagesToDiskAfterRestartTUP

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.08K pages/100 milliseconds401 - 4294967039 (0xFFFFFEFF)N

    When executing a local checkpoint, the algorithm flushes all data pages to disk. Merely doing so as quickly as possible without any moderation is likely to impose excessive loads on processors, networks, and disks. To control the write speed, this parameter specifies how many pages per 100 milliseconds are to be written. In this context, a page is defined as 8KB. This parameter is specified in units of 80KB per second, so setting NoOfDiskPagesToDiskAfterRestartTUP to a value of 20 entails writing 1.6MB in data pages to disk each second during a local checkpoint. This value includes the writing of UNDO log records for data pages. That is, this parameter handles the limitation of writes from data memory. (See the entry for IndexMemory for information about index pages.)

    In short, this parameter specifies how quickly to execute local checkpoints. It operates in conjunction with NoOfFragmentLogFiles, DataMemory, and IndexMemory.

    For more information about the interaction between these parameters and possible strategies for choosing appropriate values for them, see Section 5.3.13, “Configuring MySQL Cluster Parameters for Local Checkpoints”.

    The default value is 40 (3.2MB of data pages per second).

    Note

    This parameter is deprecated as of MySQL 5.1.6. For MySQL 5.1.12 and later versions, use DiskCheckpointSpeed and DiskSyncSize instead.

  • NoOfDiskPagesToDiskAfterRestartACC

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.08K pages/100 milliseconds201 - 4294967039 (0xFFFFFEFF)N

    This parameter uses the same units as NoOfDiskPagesToDiskAfterRestartTUP and acts in a similar fashion, but limits the speed of writing index pages from index memory.

    The default value of this parameter is 20 (1.6MB of index memory pages per second).

    Note

    This parameter is deprecated as of MySQL 5.1.6. For MySQL 5.1.12 and later versions, use DiskCheckpointSpeed and DiskSyncSize.

  • NoOfDiskPagesToDiskDuringRestartTUP (DEPRECATED)

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.08K pages/100 milliseconds401 - 4294967039 (0xFFFFFEFF)N

    This parameter is used in a fashion similar to NoOfDiskPagesToDiskAfterRestartTUP and NoOfDiskPagesToDiskAfterRestartACC, only it does so with regard to local checkpoints executed in the node when a node is restarting. A local checkpoint is always performed as part of all node restarts. During a node restart it is possible to write to disk at a higher speed than at other times, because fewer activities are being performed in the node.

    This parameter covers pages written from data memory.

    The default value is 40 (3.2MB per second).

    Note

    This parameter is deprecated as of MySQL 5.1.6. For MySQL 5.1.12 and later versions, use DiskCheckpointSpeedInRestart and DiskSyncSize.

  • NoOfDiskPagesToDiskDuringRestartACC (DEPRECATED)

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.08K pages/100 milliseconds201 - 4294967039 (0xFFFFFEFF)N

    Controls the number of index memory pages that can be written to disk during the local checkpoint phase of a node restart.

    As with NoOfDiskPagesToDiskAfterRestartTUP and NoOfDiskPagesToDiskAfterRestartACC, values for this parameter are expressed in terms of 8KB pages written per 100 milliseconds (80KB/second).

    The default value is 20 (1.6MB per second).

    Note

    This parameter is deprecated as of MySQL 5.1.6. For MySQL 5.1.12 and later versions, use DiskCheckpointSpeedInRestart and DiskSyncSize.

  • ArbitrationTimeout

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0milliseconds300010 - 4294967039 (0xFFFFFEFF)N
    NDB 7.2.0milliseconds750010 - 4294967039 (0xFFFFFEFF)N

    This parameter specifies how long data nodes wait for a response from the arbitrator to an arbitration message. If this is exceeded, the network is assumed to have split.

    In MySQL Cluster NDB 7.2.0 and later, the default value is 7500 milliseconds (7.5 seconds). Previously, this was 3000 milliseconds (3 seconds).

  • Arbitration

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.0.7enumerationDefaultDefault, Disabled, WaitExternalN

    The Arbitration parameter, added in MySQL Cluster NDB 7.0.7, enables a choice of arbitration schemes, corresponding to one of 3 possible values for this parameter:

    • Default.  This enables arbitration to proceed normally, as determined by the ArbitrationRank settings for the management and API nodes. This is the default value.

    • Disabled.  Previously, it was possible to disable arbitration only by setting ArbitrationRank to 0 on all management and API nodes. Now, you can now use Arbitration = Disabled in the [ndbd default] section of the config.ini file to accomplish this task. In this case, any ArbitrationRank settings are ignored.

    • WaitExternal.  The Arbitration parameter also makes it possible to configure arbitration in such a way that the cluster waits until after the time determined by ArbitrationTimeout has passed for an external cluster manager application to perform arbitration instead of handling arbitration internally. This can be done by setting Arbitration = WaitExternal in the [ndbd default] section of the config.ini file. For best results with the WaitExternal setting, it is recommended that ArbitrationTimeout be 2 times as long as the interval required by the external cluster manager to perform arbitration.

    Important

    This parameter should be used only in the [ndbd default] section of the cluster configuration file. The behavior of the cluster is unspecified when Arbitration is set to different values for individual data nodes.

Buffering and logging.  Several [ndbd] configuration parameters enable the advanced user to have more control over the resources used by node processes and to adjust various buffer sizes at need.

These buffers are used as front ends to the file system when writing log records to disk. If the node is running in diskless mode, these parameters can be set to their minimum values without penalty due to the fact that disk writes are faked by the NDB storage engine's file system abstraction layer.

  • UndoIndexBuffer

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0unsigned2M1M - 4294967039 (0xFFFFFEFF)N

    The UNDO index buffer, whose size is set by this parameter, is used during local checkpoints. The NDB storage engine uses a recovery scheme based on checkpoint consistency in conjunction with an operational REDO log. To produce a consistent checkpoint without blocking the entire system for writes, UNDO logging is done while performing the local checkpoint. UNDO logging is activated on a single table fragment at a time. This optimization is possible because tables are stored entirely in main memory.

    The UNDO index buffer is used for the updates on the primary key hash index. Inserts and deletes rearrange the hash index; the NDB storage engine writes UNDO log records that map all physical changes to an index page so that they can be undone at system restart. It also logs all active insert operations for each fragment at the start of a local checkpoint.

    Reads and updates set lock bits and update a header in the hash index entry. These changes are handled by the page-writing algorithm to ensure that these operations need no UNDO logging.

    This buffer is 2MB by default. The minimum value is 1MB, which is sufficient for most applications. For applications doing extremely large or numerous inserts and deletes together with large transactions and large primary keys, it may be necessary to increase the size of this buffer. If this buffer is too small, the NDB storage engine issues internal error code 677 (Index UNDO buffers overloaded).

    Important

    It is not safe to decrease the value of this parameter during a rolling restart.

  • UndoDataBuffer

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0unsigned16M1M - 4294967039 (0xFFFFFEFF)N

    This parameter sets the size of the UNDO data buffer, which performs a function similar to that of the UNDO index buffer, except the UNDO data buffer is used with regard to data memory rather than index memory. This buffer is used during the local checkpoint phase of a fragment for inserts, deletes, and updates.

    Because UNDO log entries tend to grow larger as more operations are logged, this buffer is also larger than its index memory counterpart, with a default value of 16MB.

    This amount of memory may be unnecessarily large for some applications. In such cases, it is possible to decrease this size to a minimum of 1MB.

    It is rarely necessary to increase the size of this buffer. If there is such a need, it is a good idea to check whether the disks can actually handle the load caused by database update activity. A lack of sufficient disk space cannot be overcome by increasing the size of this buffer.

    If this buffer is too small and gets congested, the NDB storage engine issues internal error code 891 (Data UNDO buffers overloaded).

    Important

    It is not safe to decrease the value of this parameter during a rolling restart.

  • RedoBuffer

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0bytes8M1M - 4294967039 (0xFFFFFEFF)N
    NDB 7.0.4bytes32M1M - 4294967039 (0xFFFFFEFF)N

    All update activities also need to be logged. The REDO log makes it possible to replay these updates whenever the system is restarted. The NDB recovery algorithm uses a fuzzy checkpoint of the data together with the UNDO log, and then applies the REDO log to play back all changes up to the restoration point.

    RedoBuffer sets the size of the buffer in which the REDO log is written. In MySQL Cluster NDB 6.4.3 and earlier, the default value is 8MB; beginning with MySQL Cluster NDB 7.0.4, the default is 32MB. The minimum value is 1MB.

    If this buffer is too small, the NDB storage engine issues error code 1221 (REDO log buffers overloaded). For this reason, you should exercise care if you attempt to decrease the value of RedoBuffer as part of an online change in the cluster's configuration.

    ndbmtd allocates a separate buffer for each LDM thread (see ThreadConfig). For example, with 4 LDM threads, an ndbmtd data node actually has 4 buffers and allocates RedoBuffer bytes to each one, for a total of 4 * RedoBuffer bytes.

  • EventLogBufferSize

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.0.4bytes81920 - 64KS

    Controls the size of the circular buffer used for NDB log events within data nodes.

    Added in MySQL Cluster NDB 7.0.4.

Controlling log messages.  In managing the cluster, it is very important to be able to control the number of log messages sent for various event types to stdout. For each event category, there are 16 possible event levels (numbered 0 through 15). Setting event reporting for a given event category to level 15 means all event reports in that category are sent to stdout; setting it to 0 means that there will be no event reports made in that category.

By default, only the startup message is sent to stdout, with the remaining event reporting level defaults being set to 0. The reason for this is that these messages are also sent to the management server's cluster log.

An analogous set of levels can be set for the management client to determine which event levels to record in the cluster log.

  • LogLevelStartup

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer10 - 15N

    The reporting level for events generated during startup of the process.

    The default level is 1.

  • LogLevelShutdown

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer00 - 15N

    The reporting level for events generated as part of graceful shutdown of a node.

    The default level is 0.

  • LogLevelStatistic

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer00 - 15N

    The reporting level for statistical events such as number of primary key reads, number of updates, number of inserts, information relating to buffer usage, and so on.

    The default level is 0.

  • LogLevelCheckpoint

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0log level00 - 15N

    The reporting level for events generated by local and global checkpoints.

    The default level is 0.

  • LogLevelNodeRestart

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer00 - 15N

    The reporting level for events generated during node restart.

    The default level is 0.

  • LogLevelConnection

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer00 - 15N

    The reporting level for events generated by connections between cluster nodes.

    The default level is 0.

  • LogLevelError

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer00 - 15N

    The reporting level for events generated by errors and warnings by the cluster as a whole. These errors do not cause any node failure but are still considered worth reporting.

    The default level is 0.

  • LogLevelCongestion

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0levelr00 - 15N

    The reporting level for events generated by congestion. These errors do not cause node failure but are still considered worth reporting.

    The default level is 0.

  • LogLevelInfo

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0integer00 - 15N

    The reporting level for events generated for information about the general state of the cluster.

    The default level is 0.

  • MemReportFrequency

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.1.0unsigned00 - 4294967039 (0xFFFFFEFF)N
    MySQL 5.1.16unsigned00 - 4294967039 (0xFFFFFEFF)N

    This parameter controls how often data node memory usage reports are recorded in the cluster log; it is an integer value representing the number of seconds between reports.

    Each data node's data memory and index memory usage is logged as both a percentage and a number of 32 KB pages of the DataMemory and IndexMemory, respectively, set in the config.ini file. For example, if DataMemory is equal to 100 MB, and a given data node is using 50 MB for data memory storage, the corresponding line in the cluster log might look like this:

    2006-12-24 01:18:16 [MgmSrvr] INFO -- Node 2: Data usage is 50%(1280 32K pages of total 2560)
    

    MemReportFrequency is not a required parameter. If used, it can be set for all cluster data nodes in the [ndbd default] section of config.ini, and can also be set or overridden for individual data nodes in the corresponding [ndbd] sections of the configuration file. The minimum value—which is also the default value—is 0, in which case memory reports are logged only when memory usage reaches certain percentages (80%, 90%, and 100%), as mentioned in the discussion of statistics events in Section 7.6.2, “MySQL Cluster Log Events”.

    This parameter was added in MySQL Cluster 5.1.16 and MySQL Cluster NDB 6.1.0.

  • StartupStatusReportFrequency

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.4.0seconds00 - 4294967039 (0xFFFFFEFF)N

    When a data node is started with the --initial, it initializes the redo log file during Start Phase 4 (see Section 7.1, “Summary of MySQL Cluster Start Phases”). When very large values are set for NoOfFragmentLogFiles, FragmentLogFileSize, or both, this initialization can take a long time. Previous to MySQL Cluster NDB 6.4.0, only the beginning and end of the redo log file initialization process were logged. Beginning with this version, it is possible to force reports on the progress of this process to be logged periodically, by means of the StartupStatusReportFrequency configuration parameter. In this case, progress is reported in the cluster log, in terms of both the number of files and the amount of space that have been initialized, as shown here:

    2009-06-20 16:39:23 [MgmSrvr] INFO -- Node 1: Local redo log file initialization status:
    #Total files: 80, Completed: 60
    #Total MBytes: 20480, Completed: 15557
    2009-06-20 16:39:23 [MgmSrvr] INFO -- Node 2: Local redo log file initialization status:
    #Total files: 80, Completed: 60
    #Total MBytes: 20480, Completed: 15570
    

    These reports are logged each StartupStatusReportFrequency seconds during Start Phase 4. If StartupStatusReportFrequency is 0 (the default), then reports are written to the cluster log only when at the beginning and at the completion of the redo log file initialization process.

Debugging Parameters.  Beginning with MySQL Cluster NDB 6.3.36, MySQL Cluster NDB 7.0.17, and MySQL Cluster NDB 7.1.6, it is possible to cause logging of traces for events generated by creating and dropping tables using DictTrace. This parameter is useful only in debugging NDB kernel code. DictTrace takes an integer value; currently, 0 (default - no logging) and 1 (logging enabled) are the only supported values.

Backup parameters.  The [ndbd] parameters discussed in this section define memory buffers set aside for execution of online backups.

  • BackupDataBufferSize

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0bytes2M0 - 4294967039 (0xFFFFFEFF)N
    NDB 6.3.23bytes16M0 - 4294967039 (0xFFFFFEFF)N
    NDB 7.0.4bytes16M0 - 4294967039 (0xFFFFFEFF)N
    NDB 7.5.1bytes16M512K - 4294967039 (0xFFFFFEFF)N

    In creating a backup, there are two buffers used for sending data to the disk. The backup data buffer is used to fill in data recorded by scanning a node's tables. Once this buffer has been filled to the level specified as BackupWriteSize, the pages are sent to disk. While flushing data to disk, the backup process can continue filling this buffer until it runs out of space. When this happens, the backup process pauses the scan and waits until some disk writes have completed freeing up memory so that scanning may continue.

    In MySQL Cluster NDB 6.4.3 and earlier, the default value is 2MB; in MySQL Cluster NDB 7.0.4 and later, it is 16MB.

  • BackupLogBufferSize

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0bytes2M0 - 4294967039 (0xFFFFFEFF)N
    NDB 6.3.23bytes16M0 - 4294967039 (0xFFFFFEFF)N
    NDB 7.0.4bytes16M0 - 4294967039 (0xFFFFFEFF)N

    The backup log buffer fulfills a role similar to that played by the backup data buffer, except that it is used for generating a log of all table writes made during execution of the backup. The same principles apply for writing these pages as with the backup data buffer, except that when there is no more space in the backup log buffer, the backup fails. For that reason, the size of the backup log buffer must be large enough to handle the load caused by write activities while the backup is being made. See Section 7.3.3, “Configuration for MySQL Cluster Backups”.

    The default value for this parameter should be sufficient for most applications. In fact, it is more likely for a backup failure to be caused by insufficient disk write speed than it is for the backup log buffer to become full. If the disk subsystem is not configured for the write load caused by applications, the cluster is unlikely to be able to perform the desired operations.

    It is preferable to configure cluster nodes in such a manner that the processor becomes the bottleneck rather than the disks or the network connections.

    In MySQL Cluster NDB 6.4.3 and earlier, the default value is 2MB; in MySQL Cluster NDB 7.0.4 and later, it is 16MB.

  • BackupMemory

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0bytes4M0 - 4294967039 (0xFFFFFEFF)N
    NDB 7.0.4bytes32M0 - 4294967039 (0xFFFFFEFF)N

    This parameter is simply the sum of BackupDataBufferSize and BackupLogBufferSize.

    In MySQL Cluster NDB 7.0.4 and later, the default value is 16MB + 16MB = 32MB. (Previously, it was 2MB + 2MB = 4MB.)

    Important

    If BackupDataBufferSize and BackupLogBufferSize taken together exceed the default value for BackupMemory, then this parameter must be set explicitly in the config.ini file to their sum.

  • BackupReportFrequency

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.2.3seconds00 - 4294967039 (0xFFFFFEFF)N

    This parameter controls how often backup status reports are issued in the management client during a backup, as well as how often such reports are written to the cluster log (provided cluster event logging is configured to permit it—see Logging and checkpointing). BackupReportFrequency represents the time in seconds between backup status reports.

    The default value is 0.

    This parameter was added in MySQL Cluster NDB 6.2.3.

  • BackupWriteSize

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0bytes32K2K - 4294967039 (0xFFFFFEFF)N
    NDB 7.0.4bytes256K2K - 4294967039 (0xFFFFFEFF)N

    This parameter specifies the default size of messages written to disk by the backup log and backup data buffers.

    In MySQL Cluster 6.4.3 and earlier, the default value for this parameter was 32KB; beginning with MySQL Cluster NDB 7.0.4, it is 256KB.

  • BackupMaxWriteSize

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.0bytes256K2K - 4294967039 (0xFFFFFEFF)N
    MySQL 5.1.32bytes1M2K - 4294967039 (0xFFFFFEFF)N
    NDB 7.2.1bytes1M2K - 4294967039 (0xFFFFFEFF)N

    This parameter specifies the maximum size of messages written to disk by the backup log and backup data buffers.

    In MySQL Cluster 6.4.3 and earlier, the default value for this parameter was 256KB; beginning with MySQL Cluster NDB 7.0.4, it is 1MB.

Important

When specifying these parameters, the following relationships must hold true. Otherwise, the data node will be unable to start.

  • BackupDataBufferSize >= BackupWriteSize + 188KB

  • BackupLogBufferSize >= BackupWriteSize + 16KB

  • BackupMaxWriteSize >= BackupWriteSize

MySQL Cluster Realtime Performance Parameters

The [ndbd] parameters discussed in this section are used in scheduling and locking of threads to specific CPUs on multiprocessor data node hosts. They were introduced in MySQL Cluster NDB 6.3.4.

Note

To make use of these parameters, the data node process must be run as system root.

  • LockExecuteThreadToCPU

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.4CPU ID64K0 - 64KN

    Previous to MySQL Cluster NDB 7.0.  This parameter specifies the ID of the CPU assigned to handle the NDBCLUSTER execution thread. The value of this parameter is an integer in the range 0 to 65535 (inclusive). The default is 65535.

    MySQL Cluster NDB 7.0 and later (beginning with MySQL Cluster NDB 6.4.0).  When used with ndbd, this parameter (now a string) specifies the ID of the CPU assigned to handle the NDBCLUSTER execution thread.

    When used with ndbmtd, the value of this parameter is a comma-separated list of CPU IDs assigned to handle execution threads. Each CPU ID in the list should be an integer in the range 0 to 65535 (inclusive). The number of IDs specified should match the number of execution threads determined by MaxNoOfExecutionThreads. However, there is no guarantee that threads are assigned to CPUs in any given order when using this parameter; beginning with in MySQL Cluster NDB 7.0.31 and MySQL Cluster NDB 7.1.20, you can obtain more finely-grained control of this type using ThreadConfig.

    LockExecuteThreadToCPU has no default value.

    Prior to MySQL Cluster NDB 7.0.18 and MySQL Cluster NDB 7.1.7, the effective maximum value recognized by this parameter as a valid CPU ID was 255; using a greater value caused thread locking to be disabled. (Bug #56185)

  • LockMaintThreadsToCPU

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.4CPU ID64K0 - 64KN
    NDB 6.4.0CPU ID[none]0 - 64KN

    This parameter specifies the ID of the CPU assigned to handle NDBCLUSTER maintenance threads.

    The value of this parameter is an integer in the range 0 to 65535 (inclusive). This parameter was added in MySQL Cluster NDB 6.3.4. Prior to MySQL Cluster NDB 6.4.0, the default is 65535; in MySQL Cluster NDB 7.0 and later MySQL Cluster release series, there is no default value.

  • RealtimeScheduler

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.4booleanfalsetrue, falseN

    Setting this parameter to 1 enables real-time scheduling of data node threads.

    Prior to MySQL Cluster NDB 7.0.40 and MySQL Cluster NDB 7.1.29, this parameter did not work correctly with data nodes running ndbmtd. (Bug #16961971)

    The default is 0 (scheduling disabled).

  • SchedulerExecutionTimer

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.4µs500 - 11000N

    This parameter specifies the time in microseconds for threads to be executed in the scheduler before being sent. Setting it to 0 minimizes the response time; to achieve higher throughput, you can increase the value at the expense of longer response times.

    The default is 50 μsec, which our testing shows to increase throughput slightly in high-load cases without materially delaying requests.

    This parameter was added in MySQL Cluster NDB 6.3.4.

  • SchedulerSpinTimer

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.4µs00 - 500N

    This parameter specifies the time in microseconds for threads to be executed in the scheduler before sleeping.

    The default value is 0.

  • BuildIndexThreads

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.30numeric00 - 128S
    NDB 7.0.11numeric00 - 128S

    This parameter determines the number of threads to create when rebuilding ordered indexes during a system or node start, as well as when running ndb_restore --rebuild-indexes. It is supported only when there is more than one fragment for the table per data node (for example, when the MAX_ROWS option has been used with CREATE TABLE).

    Setting this parameter to 0 (the default) disables multi-threaded building of ordered indexes.

    This parameter was added in MySQL Cluster NDB 6.3.30 and MySQL Cluster NDB 7.0.11. Prior to MySQL Cluster NDB 7.0.16 and MySQL Cluster NDB 7.1.5, it was supported only when using ndbd; in these and later MySQL Cluster releases, BuildIndexThreads is also supported for data nodes running ndbmtd (see Bug #54521).

    You can enable multi-threaded builds during data node initial restarts by setting the TwoPassInitialNodeRestartCopy data node configuration parameter to TRUE.

  • TwoPassInitialNodeRestartCopy

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.1.11booleanfalsetrue, falseN

    In MySQL Cluster NDB 7.1.11 and later, multi-threaded building of ordered indexes can be enabled for initial restarts of data nodes by setting this configuration parameter to TRUE, which enables two-pass copying of data during initial node restarts.

    You must also set BuildIndexThreads to a nonzero value.

  • Numa

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.0.20boolean1...N
    NDB 7.1.9boolean1...N

    This parameter determines whether Non-Uniform Memory Access (NUMA) is controlled by the operating or by the data node process, whether the data node uses ndbd or ndbmtd. By default, NDB attempts to use an interleaved NUMA memory allocation policy on any data node where the host operating system provides NUMA support.

    Setting Numa = 0 means that the datanode process does not itself attempt to set a policy for memory allocation, and permits this behavior to be determined by the operating system, which may be further guided by the separate numactl tool. That is, Numa = 0 yields the system default behavior, which can be customised by numactl. For many Linux systems, the system default behavior is to allocate socket-local memory to any given process at allocation time. This can be problematic when using ndbmtd; this is because nbdmtd allocates all memory at startup, leading to an imbalance, giving different access speeds for different sockets, especially when locking pages in main memory.

    Setting Numa = 1 means that the data node process uses libnuma to request interleaved memory allocation. (This can also be accomplished manually, on the operating system level, using numactl.) Using interleaved allocation in effect tells the data node process to ignore non-uniform memory access but does not attempt to take any advantage of fast local memory; instead, the data node process tries to avoid imbalances due to slow remote memory. If interleaved allocation is not desired, set Numa to 0 so that the desired behavior can be determined on the operating system level.

    The Numa configuration parameter is supported only on Linux systems where libnuma.so is available.

Multi-Threading Configuration Parameters (ndbmtd).  ndbmtd runs by default as a single-threaded process and must be configured to use multiple threads, using either of two methods, both of which require setting configuration parameters in the config.ini file. The first method is simply to set an appropriate value for the MaxNoOfExecutionThreads configuration parameter. In MySQL Cluster NDB 7.1.17 and later, a second method is also supported, whereby it is possible to set up more complex rules for ndbmtd multi-threading using ThreadConfig. The next few paragraphs provide information about these parameters and their use with multi-threaded data nodes.

  • MaxNoOfExecutionThreads

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.4.0integer[none]2 - 8IS
    NDB 7.0.4integer22 - 8IS

    This parameter controls the number of execution threads used by ndbmtd, up to a maximum of 8 threads, 4 of which can be LDM (LQH) threads. Although this parameter is set in the [ndbd] or [ndbd default] sections of the config.ini file, it is exclusive to ndbmtd and does not apply to ndbd.

    Setting MaxNoOfExecutionThreads sets the number of threads by type as determined in the following table:

    MaxNoOfExecutionThreads ValueLDM ThreadsTC ThreadsSend ThreadsReceive Threads
    0 .. 31101
    4 .. 62101
    7 .. 84101

    There is always one SUMA (replication) thread.

    The thread types are described later in this section (see ThreadConfig).

    Setting this parameter outside the permitted range of values causes the management server to abort on startup with the error Error line number: Illegal value value for parameter MaxNoOfExecutionThreads.

    For MaxNoOfExecutionThreads, a value of 0 or 1 is rounded up internally by NDB to 2, so that 2 is considered this parameter's default and minimum value.

    MaxNoOfExecutionThreads is generally intended to be set equal to the number of CPU threads available, and to allocate a number of threads of each type suitable to typical workloads. It does not assign particular threads to specified CPUs. For cases where it is desirable to vary from the settings provided, or to bind threads to CPUs, you should use ThreadConfig instead, which allows you to allocate each thread directly to a desired type, CPU, or both.

    The multi-threaded data node process always spawns at least 4 threads, listed here:

    • 1 local query handler (LDM) thread

    • 1 transaction coordinator (TC) thread

    • 1 receive thread

    • 1 subscription manager (SUMA or replication) thread

    Changing the number of LDM threads always requires a system restart, whether it is changed using this parameter or ThreadConfig. If the cluster's IndexMemory usage is greater than 50%, changing this requires an initial restart of the cluster. (A maximum of 30-35% IndexMemory usage is recommended in such cases.) Otherwise, resource usage and LDM thread allocation cannot be balanced between nodes, which can result in underutilized and overutilized LDM threads, and ultimately data node failures.

    In MySQL Cluster NDB 7.1 and earlier, it is not possible to cause ndbmtd to use more than 1 TC thread. (This is possible in MySQL Cluster NDB 7.2.)

  • ThreadConfig

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.1.17string''...IS
    NDB 7.2.3string''...IS

    This parameter is used with ndbmtd to assign threads of different types to different CPUs. Its value is a string whose format has the following syntax:

    ThreadConfig := entry[,entry[,...]]
    entry := type={param[,param[,...]]}
    type := ldm | main | recv | rep | io | tc | watchdog
    param := count=number
      | cpubind=cpu_list
      | cpuset=cpu_list
      | spintime=number
      | realtime={0|1}
    

    The curly braces ({...}) surrounding the list of parameters are required, even if there is only one parameter in the list.

    A param (parameter) specifies any or all of the following information:

    • The number of threads of the given type (count).

    • The set of CPUs to which the threads of the given type are to be nonexclusively bound. Thsi is determined by either one of cpubind or cpuset). cpubind causes each thread to be bound (nonexclusively) to a CPU in the set; cpuset means that each thread is bound (nonexclusively) to the set of CPUs specified.

      Only one of cpubind or cpuset can be provided in a single configuration.

    • spintime determines the wait time in microseconds the thread spins before going to sleep.

      The default value for spintime is the value of the SchedulerSpinTimer data node configuration parameter.

      spintime does not apply to I/O threads or watchdog threads and so cannot be set for these thread types.

    • realtime can be set to 0 or 1. If it is set to 1, the threads run with real-time priority. This also means that thread_prio cannot be set.

      The realtime parameter is set by default to the value of the RealtimeScheduler data node configuration parameter.

    The type attribute represents an NDB thread type. The thread types supported in MySQL Cluster NDB 7.1 and the range of permitted count values for each are provided in the following list:

    • ldm: Local query handler (DBLQH kernel block) that handles data. The more LDM threads that are used, the more highly partitioned the data becomes. Each LDM thread maintains its own sets of data and index partitions, as well as its own redo log. In MySQL Cluster NDB 7.1, the maximum is 4 such threads.

      Important

      Changing the number of LDM threads requires a system restart to be effective and safe for cluster operations. (This is also true when this is done using MaxNoOfExecutionThreads.) If IndexMemory usage is in excess of 50%, an initial restart of the cluster is required; a maximum of 30-35% IndexMemory usage is recommended in such cases. Otherwise, IndexMemory and DataMemory usage as well as the allocation of LDM threads cannot be balanced between nodes, which can ultimately lead to data node failures.

    • tc: Transaction coordinator thread (DBTC kernel block) containing the state of an ongoing transaction. In MySQL Cluster NDB 7.1, there can be only 1 TC thread. (In MySQL Cluster NDB 7.2, this number is configurable.)

      Range: 1 only.

    • main: Data dictionary and transaction coordinator (DBDIH and DBTC kernel blocks), providing schema management. This is always handled by a single dedicated thread.

      Range: 1 only.

    • recv: Receive thread (CMVMI kernel block). Each receive thread handles one or more sockets for communicating with other nodes in a MySQL Cluster, with one socket per node. Previously, this was limited to a single thread, but MySQL Cluster 7.2 implements multiple receive threads (up to 8).

      Range: 1 only.

    • rep: Replication thread (SUMA kernel block). Asynchronous replication operations are always handled by a single, dedicated thread.

      Range: 1 only.

    • io: File system and other miscellaneous operations. These are not demanding tasks, and are always handled as a group by a single, dedicated I/O thread.

      Range: 1 only.

Simple examples:

# Example 1.
ThreadConfig=ldm={count=2,cpubind=1,2},main={cpubind=12},rep={cpubind=11}
# Example 2.
Threadconfig=main={cpubind=0},ldm={count=4,cpubind=1,2,5,6},io={cpubind=3}

It is usually desirable when configuring thread usage for a data node host to reserve one or more CPUs for operating system and other tasks. Thus, for a host machine with 8 CPUs, you might want to use 8 CPU threads bound to 7 CPUs (leaving one for operating system and other functions), with 4 LDM threads, 1 TC thread, 1 receive thread, and 1 thread each for schema management, asynchronous replication, and I/O operations. (This is almost the same distribution of threads used when MaxNoOfExecutionThreads is set equal to 8.) The following ThreadConfig setting performs these assignments, additionally binding all of these threads to specific CPUs:

ThreadConfig=ldm{count=4,cpubind=1,2,3,4},main={cpubind=5}, \
io={cpubind=5},rep={cpubind=6},tc{cpubind=7},recv={cpubind=8}

It should be possible in most cases to bind the main (schema management) thread and the I/O thread to the same CPU, as we have done in the example just shown.

In order to take advantage of the enhanced stability that the use of ThreadConfig offers, it is necessary to insure that CPUs are isolated, and that they not subject to interrupts, or to being scheduled for other tasks by the operating system. On many Linux systems, you can do this by setting IRQBALANCE_BANNED_CPUS in /etc/sysconfig/irqbalance to 0xFFFFF0, and by using the isolcpus boot option in grub.conf. For specific information, see your operating system or platform documentation.

In MySQL Cluster NDB 7.1 and earlier, it is not possible to cause ndbmtd to use more than 1 TC thread; this capability is introduced in MySQL Cluster NDB 7.2.

Disk Data Configuration Parameters.  Configuration parameters affecting Disk Data behavior include the following:

  • DiskPageBufferMemory

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.1.6bytes64M4M - 1TN

    This determines the amount of space used for caching pages on disk, and is set in the [ndbd] or [ndbd default] section of the config.ini file. It is measured in bytes. Each page takes up 32 KB. This means that Cluster Disk Data storage always uses N * 32 KB memory where N is some nonnegative integer.

    The default value for this parameter is 64M (2000 pages of 32 KB each).

    This parameter was added in MySQL 5.1.6.

    Beginning with MySQL Cluster NDB 7.1.9, you can query the ndbinfo.diskpagebuffer table to help determine whether the value for this parameter should be increased to minimize unnecessary disk seeks. See Section 7.10.8, “The ndbinfo diskpagebuffer Table”, for more information.

  • SharedGlobalMemory

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.2.0bytes128M0 - 64TN
    MySQL 5.1.6bytes20M0 - 64TN

    This parameter determines the amount of memory that is used for log buffers, disk operations (such as page requests and wait queues), and metadata for tablespaces, log file groups, UNDO files, and data files. The shared global memory pool also provides memory used for satisfying the memory requirements of the UNDO_BUFFER_SIZE option used with CREATE LOGFILE GROUP and ALTER LOGFILE GROUP statements, including any default value implied for this options by the setting of the InitialLogFileGroup data node configuration parameter. SharedGlobalMemory can be set in the [ndbd] or [ndbd default] section of the config.ini configuration file, and is measured in bytes.

    As of MySQL Cluster NDB 7.2.0, the default value is 128M. (Previously, this was 20M.)

    This parameter was added in MySQL 5.1.6.

  • DiskIOThreadPool

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.4.3threads80 - 4294967039 (0xFFFFFEFF)N
    NDB 7.0.7threads20 - 4294967039 (0xFFFFFEFF)N
    NDB 7.1.0threads20 - 4294967039 (0xFFFFFEFF)N

    This parameter determines the number of unbound threads used for Disk Data file access. Before DiskIOThreadPool was introduced, exactly one thread was spawned for each Disk Data file, which could lead to performance issues, particularly when using very large data files. With DiskIOThreadPool, you can—for example—access a single large data file using several threads working in parallel.

    This parameter applies to Disk Data I/O threads only.

    The optimum value for this parameter depends on your hardware and configuration, and includes these factors:

    • Physical distribution of Disk Data files.  You can obtain better performance by placing data files, undo log files, and the data node file system on separate physical disks. If you do this with some or all of these sets of files, then you can set DiskIOThreadPool higher to enable separate threads to handle the files on each disk.

    • Disk performance and types.  The number of threads that can be accommodated for Disk Data file handling is also dependent on the speed and throughput of the disks. Faster disks and higher throughput allow for more disk I/O threads. Our test results indicate that solid-state disk drives can handle many more disk I/O threads than conventional disks, and thus higher values for DiskIOThreadPool.

    This parameter was added in MySQL Cluster NDB 6.4.0. Previous to MySQL Cluster NDB 6.4.3, it was named IOThreadPool. Previous to MySQL Cluster NDB 7.0.7, the default value was 8. Beginning with MySQL Cluster NDB 7.0.7 and MySQL Cluster NDB 7.1.0, the default is 2.

  • Disk Data file system parameters.  The parameters in the following list were added in MySQL Cluster NDB 6.2.17, 6.3.22, and 6.4.3 to make it possible to place MySQL Cluster Disk Data files in specific directories without the need for using symbolic links.

    • FileSystemPathDD

      Effective VersionType/UnitsDefaultRange/ValuesRestart Type
      NDB 6.3.22filename[see text]...IN
      NDB 6.2.17filename[see text]...IN
      NDB 6.4.3filename[see text]...IN

      If this parameter is specified, then MySQL Cluster Disk Data data files and undo log files are placed in the indicated directory. This can be overridden for data files, undo log files, or both, by specifying values for FileSystemPathDataFiles, FileSystemPathUndoFiles, or both, as explained for these parameters. It can also be overridden for data files by specifying a path in the ADD DATAFILE clause of a CREATE TABLESPACE or ALTER TABLESPACE statement, and for undo log files by specifying a path in the ADD UNDOFILE clause of a CREATE LOGFILE GROUP or ALTER LOGFILE GROUP statement. If FileSystemPathDD is not specified, then FileSystemPath is used.

      If a FileSystemPathDD directory is specified for a given data node (including the case where the parameter is specified in the [ndbd default] section of the config.ini file), then starting that data node with --initial causes all files in the directory to be deleted.

    • FileSystemPathDataFiles

      Effective VersionType/UnitsDefaultRange/ValuesRestart Type
      NDB 6.3.22filename[see text]...IN
      NDB 6.2.17filename[see text]...IN
      NDB 6.4.3filename[see text]...IN

      If this parameter is specified, then MySQL Cluster Disk Data data files are placed in the indicated directory. This overrides any value set for FileSystemPathDD. This parameter can be overridden for a given data file by specifying a path in the ADD DATAFILE clause of a CREATE TABLESPACE or ALTER TABLESPACE statement used to create that data file. If FileSystemPathDataFiles is not specified, then FileSystemPathDD is used (or FileSystemPath, if FileSystemPathDD has also not been set).

      If a FileSystemPathDataFiles directory is specified for a given data node (including the case where the parameter is specified in the [ndbd default] section of the config.ini file), then starting that data node with --initial causes all files in the directory to be deleted.

    • FileSystemPathUndoFiles

      Effective VersionType/UnitsDefaultRange/ValuesRestart Type
      NDB 6.3.22filename[see text]...IN
      NDB 6.2.17filename[see text]...IN
      NDB 6.4.3filename[see text]...IN

      If this parameter is specified, then MySQL Cluster Disk Data undo log files are placed in the indicated directory. This overrides any value set for FileSystemPathDD. This parameter can be overridden for a given data file by specifying a path in the ADD UNDO clause of a CREATE LOGFILE GROUP or ALTER LOGFILE GROUP statement used to create that data file. If FileSystemPathUndoFiles is not specified, then FileSystemPathDD is used (or FileSystemPath, if FileSystemPathDD has also not been set).

      If a FileSystemPathUndoFiles directory is specified for a given data node (including the case where the parameter is specified in the [ndbd default] section of the config.ini file), then starting that data node with --initial causes all files in the directory to be deleted.

    For more information, see Section 7.12.1, “MySQL Cluster Disk Data Objects”.

  • Disk Data object creation parameters.  The next two parameters enable you—when starting the cluster for the first time—to cause a Disk Data log file group, tablespace, or both, to be created without the use of SQL statements.

    • InitialLogFileGroup

      Effective VersionType/UnitsDefaultRange/ValuesRestart Type
      NDB 6.3.22string[see text]...S
      NDB 6.2.17string[see text]...S
      NDB 6.4.3string[see text]...S

      This parameter can be used to specify a log file group that is created when performing an initial start of the cluster. InitialLogFileGroup is specified as shown here:

      InitialLogFileGroup = [name=name;] [undo_buffer_size=size;] file-specification-list
      file-specification-list:
          file-specification[; file-specification[; ...]]
      file-specification:
          filename:size
      

      The name of the log file group is optional and defaults to DEFAULT-LG. The undo_buffer_size is also optional; if omitted, it defaults to 64M. Each file-specification corresponds to an undo log file, and at least one must be specified in the file-specification-list. Undo log files are placed according to any values that have been set for FileSystemPath, FileSystemPathDD, and FileSystemPathUndoFiles, just as if they had been created as the result of a CREATE LOGFILE GROUP or ALTER LOGFILE GROUP statement.

      Consider the following:

      InitialLogFileGroup = name=LG1; undo_buffer_size=128M; undo1.log:250M; undo2.log:150M
      

      This is equivalent to the following SQL statements:

      CREATE LOGFILE GROUP LG1
          ADD UNDOFILE 'undo1.log'
          INITIAL_SIZE 250M
          UNDO_BUFFER_SIZE 128M
          ENGINE NDBCLUSTER;
      ALTER LOGFILE GROUP LG1
          ADD UNDOFILE 'undo2.log'
          INITIAL_SIZE 150M
          ENGINE NDBCLUSTER;
      

      This logfile group is created when the data nodes are started with --initial.

      Resources for the initial log file group are taken from the global memory pool whose size is determined by the value of the SharedGlobalMemory data node configuration parameter; if this parameter is set too low and the values set in InitialLogFileGroup for the logfile group's initial size or undo buffer size are too high, the cluster may fail to create the default log file group when starting, or fail to start altogether.

      This parameter, if used, should always be set in the [ndbd default] section of the config.ini file. The behavior of a MySQL Cluster when different values are set on different data nodes is not defined.

    • InitialTablespace

      Effective VersionType/UnitsDefaultRange/ValuesRestart Type
      NDB 6.3.22string[see text]...S
      NDB 6.2.17string[see text]...S
      NDB 6.4.3string[see text]...S

      This parameter can be used to specify a MySQL Cluster Disk Data tablespace that is created when performing an initial start of the cluster. InitialTablespace is specified as shown here:

      InitialTablespace = [name=name;] [extent_size=size;] file-specification-list
      

      The name of the tablespace is optional and defaults to DEFAULT-TS. The extent_size is also optional; it defaults to 1M. The file-specification-list uses the same syntax as shown with the InitialLogfileGroup parameter, the only difference being that each file-specification used with InitialTablespace corresponds to a data file. At least one must be specified in the file-specification-list. Data files are placed according to any values that have been set for FileSystemPath, FileSystemPathDD, and FileSystemPathDataFiles, just as if they had been created as the result of a CREATE TABLESPACE or ALTER TABLESPACE statement.

      For example, consider the following line specifying InitialTablespace in the [ndbd default] section of the config.ini file (as with InitialLogfileGroup, this parameter should always be set in the [ndbd default] section, as the behavior of a MySQL Cluster when different values are set on different data nodes is not defined):

      InitialTablespace = name=TS1; extent_size=8M; data1.dat:2G; data2.dat:4G
      

      This is equivalent to the following SQL statements:

      CREATE TABLESPACE TS1
          ADD DATAFILE 'data1.dat'
          EXTENT_SIZE 8M
          INITIAL_SIZE 2G
          ENGINE NDBCLUSTER;
      ALTER TABLESPACE TS1
          ADD DATAFILE 'data2.dat'
          INITIAL_SIZE 4G
          ENGINE NDBCLUSTER;
      

      This tablespace is created when the data nodes are started with --initial, and can be used whenever creating MySQL Cluster Disk Data tables thereafter.

Disk Data and GCP Stop errors.  Errors encountered when using Disk Data tables such as Node nodeid killed this node because GCP stop was detected (error 2303) are often referred to as GCP stop errors. Such errors occur when the redo log is not flushed to disk quickly enough; this is usually due to slow disks and insufficient disk throughput.

You can help prevent these errors from occurring by using faster disks, and by placing Disk Data files on a separate disk from the data node file system. Reducing the value of TimeBetweenGlobalCheckpoints tends to decrease the amount of data to be written for each global checkpoint, and so may provide some protection against redo log buffer overflows when trying to write a global checkpoint; however, reducing this value also permits less time in which to write the GCP, so this must be done with caution.

In addition, adjusting the cluster configuration as discussed here can also help:

  • MySQL Cluster NDB 6.2 and 6.3.  When working with large amounts of data on disk under high load, the default value for DiskPageBufferMemory may not be large enough. In such cases, you should increase its value to include most of the memory available to the data nodes after accounting for index memory, data memory, internal buffers, and memory needed by the data node host operating system.

    You can use this formula as a guide:

    DiskPageBufferMemory
      = 0.8
        x (
            [total memory]
              - ([operating system memory] + [buffer memory] + DataMemory + IndexMemory)
          )
    

    Once you have established that sufficient memory is reserved for DataMemory, IndexMemory, NDB internal buffers, and operating system overhead, it is possible (and sometimes desirable) to allocate more than the above amount of the remainder to DiskPageBufferMemory.

  • MySQL Cluster NDB 7.X.  In addition to the considerations given for DiskPageBufferMemory as explained previously, it is also very important that the DiskIOThreadPool configuration parameter be set correctly; having DiskIOThreadPool set too high is very likely to cause GCP stop errors (Bug #37227).

GCP stops can be caused by save or commit timeouts; the TimeBetweenEpochsTimeout data node configuration parameter determines the timeout for commits. However, beginning with MySQL Cluster NDB 7.0.21 and MySQL Cluster NDB 7.1.10, it is possible to disable both types of timeouts by setting this parameter to 0.

Parameters for configuring send buffer memory allocation (MySQL Cluster NDB 7.0 and later).  Beginning with MySQL Cluster NDB 6.4.0, send buffer memory is allocated dynamically from a memory pool shared between all transporters, which means that the size of the send buffer can be adjusted as necessary. (Previously, the NDB kernel used a fixed-size send buffer for every node in the cluster, which was allocated when the node started and could not be changed while the node was running.) The following data node configuration parameters were added in MySQL Cluster NDB 6.4.0 to permit the setting of limits on this memory allocation; this change is reflected by the addition of the configuration parameters TotalSendBufferMemory and OverLoadLimit, as well as a change in how the existing SendBufferMemory configuration parameter is used. For more information, see Section 5.3.14, “Configuring MySQL Cluster Send Buffer Parameters”.

  • ExtraSendBufferMemory

    This parameter specifies the amount of transporter send buffer memory to allocate in addition to any set using TotalSendBufferMemory, SendBufferMemory, or both.

    This parameter was added in MySQL Cluster NDB 7.0.31 and MySQL Cluster NDB 7.1.20. (Bug #13633845, Bug #11760629, Bug #53053)

  • TotalSendBufferMemory

    This parameter is available beginning with MySQL Cluster NDB 6.4.0. It is used to determine the total amount of memory to allocate on this node for shared send buffer memory among all configured transporters.

    Prior to MySQL Cluster NDB 7.0.31 and MySQL Cluster NDB 7.1.20, this parameter did not work correctly with ndbmtd. (Bug #13633845)

    If this parameter is set, its minimum permitted value is 256KB; 0 indicates that the parameter has not been set. For more detailed information, see Section 5.3.14, “Configuring MySQL Cluster Send Buffer Parameters”.

  • ReservedSendBufferMemory

    This parameter is present in NDBCLUSTER source code beginning with MySQL Cluster NDB 6.4.0. However, it is not currently enabled.

    As of MySQL Cluster NDB 7.0.31 and MySQL Cluster NDB 7.1.20, this parameter is deprecated, and is subject to removal in a future release of MySQL Cluster (Bug #11760629, Bug #53053).

For more detailed information about the behavior and use of TotalSendBufferMemory and ReservedSendBufferMemory, and about configuring send buffer memory parameters in MySQL Cluster NDB 6.4.0 and later, see Section 5.3.14, “Configuring MySQL Cluster Send Buffer Parameters”.

Note

Previous to MySQL Cluster NDB 7.0, to add new data nodes to a MySQL Cluster, it was necessary to shut down the cluster completely, update the config.ini file, and then restart the cluster (that is, you had to perform a system restart). All data node processes had to be started with the --initial option.

Beginning with MySQL Cluster NDB 7.0, it is possible to add new data node groups to a running cluster online. See Section 7.13, “Adding MySQL Cluster Data Nodes Online”, for more information.

Redo log over-commit handling.  Beginning with MySQL Cluster NDB 7.1.10, it is possible to control the data node's handling of operations when too much time is taken flushing redo logs to disk. This occurs when a given redo log flush takes longer than RedoOverCommitLimit seconds, more than RedoOverCommitCounter times, causing any pending transactions to be aborted. When this happens, the API node that sent the transaction can handle the operations that should have been committed either by queuing the operations and re-trying them, or by aborting them, as determined by DefaultOperationRedoProblemAction. The data node configuration parameters for setting the timeout and number of times it may be exceeded before the API node takes this action are described in the following list:

  • RedoOverCommitCounter

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.1.10numeric30 - 4294967039 (0xFFFFFEFF)N

    When RedoOverCommitLimit is exceeded when trying to write a given redo log to disk this many times or more, any transactions that were not committed as a result are aborted, and an API node where any of these transactions originated handles the operations making up those transactions according to its value for DefaultOperationRedoProblemAction (by either queuing the operations to be re-tried, or aborting them).

    RedoOverCommitCounter defaults to 3. Set it to 0 to disable the limit. This parameter was added in MySQL Cluster NDB 7.1.10.

  • RedoOverCommitLimit

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 7.1.10seconds200 - 4294967039 (0xFFFFFEFF)N

    This parameter sets an upper limit in seconds for trying to write a given redo log to disk before timing out. The number of times the data node tries to flush this redo log, but takes longer than RedoOverCommitLimit, is kept and compared with RedoOverCommitCounter, and when flushing takes too long more times than the value of that parameter, any transactions that were not committed as a result of the flush timeout are aborted. When this occurs, the API node where any of these transactions originated handles the operations making up those transactions according to its DefaultOperationRedoProblemAction setting (it either queues the operations to be re-tried, or aborts them).

    By default, RedoOverCommitLimit is 20 seconds. Set to 0 to disable checking for redo log flush timeouts. This parameter was added in MySQL Cluster NDB 7.1.10.

Controlling restart attempts.  Beginning in MySQL Cluster NDB 6.2.19, MySQL Cluster NDB 6.3.37, MySQL Cluster NDB 7.0.18, and MySQL Cluster NDB 7.1.7, it is possible to exercise more finely-grained control over restart attempts by data nodes when they fail to start using two data node configuration parameters added in these releases. MaxStartFailRetries limits the total number of retries made before giving up on starting the data node; StartFailRetryDelay sets the number of seconds between retry attempts, as described in the following list:

  • StartFailRetryDelay

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.37unsigned00 - 4294967039 (0xFFFFFEFF)N
    NDB 7.0.18unsigned00 - 4294967039 (0xFFFFFEFF)N
    NDB 7.1.7unsigned00 - 4294967039 (0xFFFFFEFF)N
    NDB 6.2.19unsigned00 - 4294967039 (0xFFFFFEFF)N

    Beginning in MySQL Cluster NDB 6.2.19, MySQL Cluster NDB 6.3.37, MySQL Cluster NDB 7.0.18, and MySQL Cluster NDB 7.1.7, it is possible to set the number of seconds between restart attempts by the data node in the event on failure on startup. The default is 0 (no delay).

    Note

    This parameter is ignored unless StopOnError is equal to 0.

  • MaxStartFailRetries

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    NDB 6.3.37unsigned30 - 4294967039 (0xFFFFFEFF)N
    NDB 7.0.18unsigned30 - 4294967039 (0xFFFFFEFF)N
    NDB 7.1.7unsigned30 - 4294967039 (0xFFFFFEFF)N
    NDB 6.2.19unsigned30 - 4294967039 (0xFFFFFEFF)N

    Beginning in MySQL Cluster NDB 6.2.19, MySQL Cluster NDB 6.3.37, MySQL Cluster NDB 7.0.18, and MySQL Cluster NDB 7.1.7, it is possible to limit the number restart attempts made by the data node in the event that it fails on startup. The default is 3 attempts.

    Note

    This parameter is ignored unless StopOnError is equal to 0.