MySQL 5.0 Reference Manual  /  ...  /  Defining MySQL Cluster Data Nodes Defining MySQL Cluster Data Nodes

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

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.

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, Id 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.

Identifying data nodes.  The 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 5.0.0unsigned[none]1 - 48IS

    This is the node ID used as the address of the node 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.

    In MySQL 5.0.15 and later, NodeId is a synonym for this parameter, and is the preferred form. In MySQL Cluster NDB 6.2 and later, Id is deprecated in favor of NodeId for identifying data nodes.

  • NodeId

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.15unsigned[none]1 - 48IS

    Beginning with MySQL 5.0.15, NodeId is available as a synonym for Id.

    In MySQL Cluster NDB 6.2 and later, Id is deprecated in favor of NodeId for identifying management nodes.

  • ExecuteOnComputer

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0name[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 5.0.0name 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 5.0.0unsigned[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.


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

  • NoOfReplicas

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer[none]1 - 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.

    There is no default value for NoOfReplicas; the recommended value is 2 for most common usage scenarios.

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


    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 5.0.0path....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 5.0.0pathDataDir...IN

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


    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 5.0.0path[see text]...IN

    This parameter specifies the directory in which backups are placed.


    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 5.0.0bytes80M1M - 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. Each record is currently of fixed size. (Even VARCHAR columns are stored as fixed-width columns.) 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.

    The maximum record size is currently 8052 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.

    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.

    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 5.0.0bytes18M1M - 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. Note that when defining a primary key and a unique index, two indexes will be created, one of which is a hash index used for all tuple accesses as well as lock handling. It is also used to enforce unique constraints.

    The size of the hash index is 25 bytes per record, plus the size of the primary key. For primary keys larger than 32 bytes another 8 bytes is added.

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

  • StringMemory

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0% or bytes00 - 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. In general it is safe to assume that the maximum default value is approximately 5 MB for a MySQL Cluster having 1000 tables.

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

    In MySQL 5.0, the default value is 100—that is, 100 percent of the default maximum, or roughly 5 MB. It is possible to reduce this value safely, but it should never be less than 5 percent. If you encounter Error 773 Out of string memory, please modify StringMemory config parameter: Permanent error: Schema error, this means that means that you have set the StringMemory value too low. 25 (25 percent) is not excessive, and should prevent this error from recurring in all but the most extreme conditions, as when there are hundreds or thousands of NDB tables with names whose lengths and columns whose number approach their permitted maximums.

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

CREATE TABLE example (

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.

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 three [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.

  • MaxNoOfConcurrentTransactions

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer409632 - 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 SQL nodes. Each such connection 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 insuring 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 5.0.0integer32K32 - 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 5.0.0integerUNDEFINED32 - 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.

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 5.0.0integer8K0 - 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 5.0.0integer40000 - 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 5.0.0bytes1M1K - 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 5.0.0integer2562 - 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 5.0.0integer[see text]32 - 4294967039 (0xFFFFFEFF)N

    Specifies the number of local scan records if many scans are not fully parallelized. If the number of local scan records is not provided, it is calculated as the product of MaxNoOfConcurrentScans and the number of data nodes in the system, plus 2. The minimum value is 32.

  • BatchSizePerLocalScan

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer641 - 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 5.0.0bytes1M512K - 4294967039 (0xFFFFFEFF)N

    This is an internal buffer used for passing messages within individual nodes and between nodes. Although it is highly unlikely that this would need to be changed, it is configurable. By default, it is set to 1MB.

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

  • NoOfFragmentLogFiles

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer83 - 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 three local checkpoints have been completed since that log record was inserted. 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, “Configuring MySQL Cluster Parameters for Local Checkpoints”.

    The default parameter value is 8, which means 8 sets of 4 16MB files for a total of 512MB. In other words, REDO log space is always allocated in blocks of 64MB. 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.


    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).

  • MaxNoOfOpenFiles

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer4020 - 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 40.

  • MaxNoOfSavedMessages

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer250 - 4294967039 (0xFFFFFEFF)N

    This parameter sets the maximum number of trace files that are kept before overwriting old ones. Trace files are generated when, for whatever reason, the node crashes.

    The default is 25 trace files.

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 5.0.0integer100032 - 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.

    A known issue in MySQL Cluster in MySQL 5.0 is that this parameter is occasionally treated as a hard limit for certain operations. This can lead to confusion when it is sometimes possible (or not possible, depending on the circumstances) to create more than MaxNoOfAttributes attributes. This is fixed in MySQL Cluster NDB 6.3 and later. (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 the total number of MySQL Cluster tables. 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 5.0.0integer1288 - 1600N
    MySQL 5.0.0integer1288 - 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.

    A known issue in MySQL Cluster in MySQL 5.0 is that this parameter is occasionally treated as a hard limit for certain operations. This can lead to confusion when it is sometimes possible (or not possible, depending on the circumstances) to create more than MaxNoOfTables tables. This is fixed in MySQL Cluster NDB 6.3 and later. (Bug #61684)

    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. (This is a change from MySQL 4.1.) Each table object consumes approximately 20KB per node.


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

  • MaxNoOfOrderedIndexes

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer1280 - 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 hash indexes that can be in use in the system at any one time.

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


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

  • MaxNoOfUniqueHashIndexes

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer640 - 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.


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

  • MaxNoOfTriggers

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer7680 - 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.

    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.

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.

  • LockPagesInMainMemory

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0true|false (1|0)00 - 1N
    MySQL 5.0.0true|false (1|0)00 - 1N
    MySQL 5.0.36numeric00 - 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 5.0.36, 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.


    Beginning with MySQL 5.0.36, 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.


    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


    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 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 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 5.0.0boolean10, 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.

  • Diskless

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0true|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.


    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.

  • RestartOnErrorInsert

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0error 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.

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 5.0.0milliseconds600070 - 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 4000 milliseconds (4 seconds).

  • StartPartialTimeout

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0milliseconds300000 - 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 5.0.0milliseconds600000 - 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 5.0.0milliseconds00 - 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.

  • HeartbeatIntervalDbDb

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0milliseconds150010 - 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.

    The default heartbeat interval is 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 5.0.0milliseconds1500100 - 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.

  • TimeBetweenLocalCheckpoints

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0number 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 5.0.0milliseconds200010 - 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.

  • TimeBetweenInactiveTransactionAbortCheck

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0milliseconds10001000 - 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 5.0.0milliseconds[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 5.0.0milliseconds120050 - 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 5.0.20 and earlier versions, setting it too high could cause undesirable behavior in situations involving deadlocks and node failure. Beginning with MySQL 5.0.21, 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). The effective minimum value is 100 milliseconds; it is possible to set it as low as 50 milliseconds, but any such value is treated as 100 ms. (Bug #44099)

  • NoOfDiskPagesToDiskAfterRestartTUP

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.08K 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. UNDO log records for index pages are handled by the parameter NoOfDiskPagesToDiskAfterRestartACC. (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, “Configuring MySQL Cluster Parameters for Local Checkpoints”.

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

  • NoOfDiskPagesToDiskAfterRestartACC

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.08K 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).

  • NoOfDiskPagesToDiskDuringRestartTUP

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.08K 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).

  • NoOfDiskPagesToDiskDuringRestartACC

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.08K 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).

  • ArbitrationTimeout

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0milliseconds300010 - 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.

    The default value is 1000 milliseconds (1 second).

Buffering and logging.  Several [ndbd] configuration parameters corresponding to former compile-time parameters were introduced in MySQL 4.1.5. These 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 5.0.0unsigned2M1M - 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).


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

  • UndoDataBuffer

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0unsigned16M1M - 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).


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

  • RedoBuffer

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0bytes8M1M - 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, and is 8MB by default. The minimum value is 1MB.

    If this buffer is too small, the NDB storage engine issues error code 1221 (REDO log buffers overloaded).


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

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 5.0.0integer10 - 15N

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

    The default level is 1.

  • LogLevelShutdown

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer00 - 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 5.0.0integer00 - 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 5.0.0log 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 5.0.0integer00 - 15N

    The reporting level for events generated during node restart.

    The default level is 0.

  • LogLevelConnection

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer00 - 15N

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

    The default level is 0.

  • LogLevelError

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0integer00 - 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 5.0.0levelr00 - 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 5.0.0integer00 - 15N

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

    The default level is 0.

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 5.0.0bytes2M0 - 4294967039 (0xFFFFFEFF)N
    NDB 7.5.0bytes16M2M - 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 (see below), 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.

    The default value is 2MB.

  • BackupLogBufferSize

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0bytes2M0 - 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, “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.

    The default value is 2MB.

  • BackupMemory

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0bytes4M0 - 4294967039 (0xFFFFFEFF)N

    This parameter is simply the sum of BackupDataBufferSize and BackupLogBufferSize.

    The default value is 2MB + 2MB = 4MB.


    If BackupDataBufferSize and BackupLogBufferSize taken together exceed 4MB, then this parameter must be set explicitly in the config.ini file to their sum.

  • BackupWriteSize

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0bytes32K2K - 4294967039 (0xFFFFFEFF)N

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

    The default value is 32KB.

  • BackupMaxWriteSize

    Effective VersionType/UnitsDefaultRange/ValuesRestart Type
    MySQL 5.0.0bytes256K2K - 4294967039 (0xFFFFFEFF)N

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

    The default value is 256KB.


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


To add new data nodes to a MySQL Cluster, it is necessary to shut down the cluster completely, update the config.ini file, and then restart the cluster (that is, you must perform a system restart). All data node processes must 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; however, we do not plan to implement this change in MySQL 5.0.

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