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5.3.9.2 NDB Cluster System Variables

This section provides detailed information about MySQL server system variables that are specific to NDB Cluster and the NDB storage engine. For system variables not specific to NDB Cluster, see Server System Variables. For general information on using system variables, see Using System Variables.

  • ndb_autoincrement_prefetch_sz

    Table 5.228 Type and value information for ndb_autoincrement_prefetch_sz

    Property Value
    Name ndb_autoincrement_prefetch_sz
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Both
    Dynamic Yes
    Type
    Default, Range 32 / 1 - 256 (Version: NDB 7.5-7.6)
    Default, Range 1 / 1 - 256 (Version: 5.0.56)
    Default, Range 32 / 1 - 256 (Version: 5.1.1)
    Default, Range 1 / 1 - 256 (Version: 5.1.23)
    Default, Range 32 / 1 - 256 (Version: 5.1.16-ndb-6.2.0)
    Default, Range 1 / 1 - 256 (Version: 5.1.23-ndb-6.2.10)
    Default, Range 32 / 1 - 256 (Version: 5.1.19-ndb-6.3.0)
    Default, Range 1 / 1 - 256 (Version: 5.1.23-ndb-6.3.7)
    Default, Range 1 / 1 - 65536 (Version: 5.1.41-ndb-6.3.31)
    Default, Range 32 / 1 - 256 (Version: 5.1.30-ndb-6.4.0)
    Default, Range 1 / 1 - 65536 (Version: 5.1.41-ndb-7.0.11)
    Default, Range 1 / 1 - 65536 (Version: 5.5.15-ndb-7.2.1)
    Notes

    DESCRIPTION: NDB auto-increment prefetch size


    Determines the probability of gaps in an autoincremented column. Set it to 1 to minimize this. Setting it to a high value for optimization makes inserts faster, but decreases the likelihood that consecutive autoincrement numbers will be used in a batch of inserts. The mininum and default value is 1. The maximum value for ndb_autoincrement_prefetch_sz is 65536.

    This variable affects only the number of AUTO_INCREMENT IDs that are fetched between statements; within a given statement, at least 32 IDs are obtained at a time. The default value is 1.

    Important

    This variable does not affect inserts performed using INSERT ... SELECT.

  • ndb_cache_check_time

    Table 5.229 Type and value information for ndb_cache_check_time

    Property Value
    Name ndb_cache_check_time
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range 0 / - (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Number of milliseconds between checks of cluster SQL nodes made by the MySQL query cache


    The number of milliseconds that elapse between checks of NDB Cluster SQL nodes by the MySQL query cache. Setting this to 0 (the default and minimum value) means that the query cache checks for validation on every query.

    The recommended maximum value for this variable is 1000, which means that the check is performed once per second. A larger value means that the check is performed and possibly invalidated due to updates on different SQL nodes less often. It is generally not desirable to set this to a value greater than 2000.

    Note

    The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes ndb_cache_check_time.

  • ndb_clear_apply_status

    Table 5.230 Type and value information for ndb_clear_apply_status

    Property Value
    Name ndb_clear_apply_status
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File No
    Scope Global
    Dynamic Yes
    Type
    Default, Range ON (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Causes RESET SLAVE to clear all rows from the ndb_apply_status table; ON by default


    By the default, executing RESET SLAVE causes an NDB Cluster replication slave to purge all rows from its ndb_apply_status table. You can disable this by setting ndb_clear_apply_status=OFF.

  • ndb_data_node_neighbour

    Table 5.231 Type and value information for ndb_data_node_neighbour

    Property Value
    Name ndb_data_node_neighbour
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range 0 / 0 - 255 (Version: 5.7.12-ndb-7.5.2)
    Notes

    DESCRIPTION: Specifies cluster data node "closest" to this MySQL Server, for transaction hinting and fully replicated tables


    Sets the ID of a nearest data node—that is, a preferred nonlocal data node is chosen to execute the transaction, rather than one running on the same host as the SQL or API node. This used to ensure that when a fully replicated table is accessed, we access it on this data node, to ensure that the local copy of the table is always used whenever possible. This can also be used for providing hints for transactions.

    This can improve data access times in the case of a node that is physically closer than and thus has higher network throughput than others on the same host.

    See Setting NDB_TABLE Options, for further information.

    Added in NDB 7.5.2.

    Note

    An equivalent method set_data_node_neighbour() is provided for use in NDB API applications.

  • ndb_default_column_format

    Table 5.232 Type and value information for ndb_default_column_format

    Property Value
    Name ndb_default_column_format
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range DYNAMIC / FIXED, DYNAMIC (Version: 5.7.11-ndb-7.5.1)
    Default, Range FIXED / FIXED, DYNAMIC (Version: 5.7.16-ndb-7.5.4)
    Notes

    DESCRIPTION: Sets default row format and column format (FIXED or DYNAMIC) used for new NDB tables


    In NDB 7.5.1 and later, sets the default COLUMN_FORMAT and ROW_FORMAT for new tables (see CREATE TABLE Syntax).

    In NDB 7.5.1, the default for this variable was DYNAMIC; in NDB 7.5.4, the default was changed to FIXED to maintain backwards compatibility with older release series (Bug #24487363).

  • ndb_deferred_constraints

    Table 5.233 Type and value information for ndb_deferred_constraints

    Property Value
    Name ndb_deferred_constraints
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Both
    Dynamic Yes
    Type
    Default, Range 0 / 0 - 1 (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Specifies that constraint checks should be deferred (where these are supported). Not normally needed or used; for testing purposes only.


    Controls whether or not constraint checks are deferred, where these are supported. 0 is the default.

    This variable is not normally needed for operation of NDB Cluster or NDB Cluster Replication, and is intended primarily for use in testing.

  • ndb_distribution

    Table 5.234 Type and value information for ndb_distribution

    Property Value
    Name ndb_distribution
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range KEYHASH / LINHASH, KEYHASH (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Default distribution for new tables in NDBCLUSTER (KEYHASH or LINHASH, default is KEYHASH)


    Controls the default distribution method for NDB tables. Can be set to either of KEYHASH (key hashing) or LINHASH (linear hashing). KEYHASH is the default.

  • ndb_eventbuffer_free_percent

    Table 5.235 Type and value information for ndb_eventbuffer_free_percent

    Property Value
    Name ndb_eventbuffer_free_percent
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range 20 / 1 - 99 (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Percentage of free memory that should be available in event buffer before resumption of buffering, after reaching limit set by ndb_eventbuffer_max_alloc


    Sets the percentage of the maximum memory allocated to the event buffer (ndb_eventbuffer_max_alloc) that should be available in event buffer after reaching the maximum, before starting to buffer again.

  • ndb_eventbuffer_max_alloc

    Table 5.236 Type and value information for ndb_eventbuffer_max_alloc

    Property Value
    Name ndb_eventbuffer_max_alloc
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range 0 / 0 - 4294967295 (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Maximum memory that can be allocated for buffering events by the NDB API. Defaults to 0 (no limit).


    Sets the maximum amount memory (in bytes) that can be allocated for buffering events by the NDB API. 0 means that no limit is imposed, and is the default.

  • ndb_extra_logging

    Table 5.237 Type and value information for ndb_extra_logging

    Property Value
    Name ndb_extra_logging
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range 0 / - (Version: NDB 7.5-7.6)
    Default, Range 1 / - (Version: 5.1.19-ndb-6.3.0)
    Notes

    DESCRIPTION: Controls logging of NDB Cluster schema, connection, and data distribution events in the MySQL error log


    This variable enables recording in the MySQL error log of information specific to the NDB storage engine.

    When this variable is set to 0, the only information specific to NDB that is written to the MySQL error log relates to transaction handling. If it set to a value greater than 0 but less than 10, NDB table schema and connection events are also logged, as well as whether or not conflict resolution is in use, and other NDB errors and information. If the value is set to 10 or more, information about NDB internals, such as the progress of data distribution among cluster nodes, is also written to the MySQL error log. The default is 1.

  • ndb_force_send

    Table 5.238 Type and value information for ndb_force_send

    Property Value
    Name ndb_force_send
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Both
    Dynamic Yes
    Type
    Default, Range TRUE (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Forces sending of buffers to NDB immediately, without waiting for other threads


    Forces sending of buffers to NDB immediately, without waiting for other threads. Defaults to ON.

  • ndb_fully_replicated

    Table 5.239 Type and value information for ndb_fully_replicated

    Property Value
    Name ndb_fully_replicated
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Both
    Dynamic Yes
    Type
    Default, Range OFF (Version: 5.7.12-ndb-7-5-2)
    Notes

    DESCRIPTION: Whether new NDB tables are fully replicated


    Determines whether new NDB tables are fully replicated. This setting can be overridden for an individual table using COMMENT="NDB_TABLE=FULLY_REPLICATED=..." in a CREATE TABLE or ALTER TABLE statement; see Setting NDB_TABLE Options, for syntax and other information.

    Added in NDB 7.5.2.

  • ndb_index_stat_enable

    Table 5.240 Type and value information for ndb_index_stat_enable

    Property Value
    Name ndb_index_stat_enable
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Both
    Dynamic Yes
    Type
    Default, Range OFF (Version: NDB 7.5-7.6)
    Default, Range ON (Version: 5.5.15-ndb-7.2.1)
    Notes

    DESCRIPTION: Use NDB index statistics in query optimization


    Use NDB index statistics in query optimization. The default is ON.

  • ndb_index_stat_option

    Table 5.241 Type and value information for ndb_index_stat_option

    Property Value
    Name ndb_index_stat_option
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Both
    Dynamic Yes
    Type
    Default, Range loop_enable=1000ms,loop_idle=1000ms,loop_busy=100ms, update_batch=1,read_batch=4,idle_batch=32,check_batch=8, check_delay=10m,delete_batch=8, clean_delay=1m,error_batch=4, error_delay=1m,evict_batch=8,evict_delay=1m,cache_limit=32M, cache_lowpct=90,zero_total=0 (Version: NDB 7.5-7.6)
    Default, Range loop_checkon=1000ms,loop_idle=1000ms,loop_busy=100ms, update_batch=1,read_batch=4,idle_batch=32,check_batch=32, check_delay=1m,delete_batch=8,clean_delay=0,error_batch=4, error_delay=1m,evict_batch=8,evict_delay=1m,cache_limit=32M, cache_lowpct=90 (Version: 5.1.56-ndb-7.1.17)
    Notes

    DESCRIPTION: Comma-separated list of tunable options for NDB index statistics; the list should contain no spaces


    This variable is used for providing tuning options for NDB index statistics generation. The list consist of comma-separated name-value pairs of option names and values, and this list must not contain any space characters.

    Options not used when setting ndb_index_stat_option are not changed from their default values. For example, you can set ndb_index_stat_option = 'loop_idle=1000ms,cache_limit=32M'.

    Time values can be optionally suffixed with h (hours), m (minutes), or s (seconds). Millisecond values can optionally be specified using ms; millisecond values cannot be specified using h, m, or s.) Integer values can be suffixed with K, M, or G.

    The names of the options that can be set using this variable are shown in the table that follows. The table also provides brief descriptions of the options, their default values, and (where applicable) their minimum and maximum values.

    Table 5.242 ndb_index_stat_option options and values

    Name Description Default/Units Minimum/Maximum
    loop_enable 1000 ms 0/4G
    loop_idle Time to sleep when idle 1000 ms 0/4G
    loop_busy Time to sleep when more work is waiting 100 ms 0/4G
    update_batch 1 0/4G
    read_batch 4 1/4G
    idle_batch 32 1/4G
    check_batch 8 1/4G
    check_delay How often to check for new statistics 10 m 1/4G
    delete_batch 8 0/4G
    clean_delay 1 m 0/4G
    error_batch 4 1/4G
    error_delay 1 m 1/4G
    evict_batch 8 1/4G
    evict_delay Clean LRU cache, from read time 1 m 0/4G
    cache_limit Maximum amount of memory in bytes used for cached index statistics by this mysqld; clean up the cache when this is exceeded. 32 M 0/4G
    cache_lowpct 90 0/100
    zero_total Setting this to 1 resets all accumulating counters in ndb_index_stat_status to 0. This option value is also reset to 0 when this is done. 0 0/1

  • ndb_join_pushdown

    Table 5.243 Type and value information for ndb_join_pushdown

    Property Value
    Name ndb_join_pushdown
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Both
    Dynamic Yes
    Type
    Default, Range TRUE (Version: 5.1.51-ndb-7.2.0)
    Notes

    DESCRIPTION: Enables pushing down of joins to data nodes


    This variable controls whether joins on NDB tables are pushed down to the NDB kernel (data nodes). Previously, a join was handled using multiple accesses of NDB by the SQL node; however, when ndb_join_pushdown is enabled, a pushable join is sent in its entirety to the data nodes, where it can be distributed among the data nodes and executed in parallel on multiple copies of the data, with a single, merged result being returned to mysqld. This can reduce greatly the number of round trips between an SQL node and the data nodes required to handle such a join.

    By default, ndb_join_pushdown is enabled.

    Conditions for NDB pushdown joins.  In order for a join to be pushable, it must meet the following conditions:

    1. Only columns can be compared, and all columns to be joined must use exactly the same data type.

      This means that expressions such as t1.a = t2.a + constant cannot be pushed down, and that (for example) a join on an INT column and a BIGINT column also cannot be pushed down.

    2. Queries referencing BLOB or TEXT columns are not supported.

    3. Explicit locking is not supported; however, the NDB storage engine's characteristic implicit row-based locking is enforced.

      This means that a join using FOR UPDATE cannot be pushed down.

    4. In order for a join to be pushed down, child tables in the join must be accessed using one of the ref, eq_ref, or  const access methods, or some combination of these methods.

      Outer joined child tables can only be pushed using eq_ref.

      If the root of the pushed join is an eq_ref or const, only child tables joined by eq_ref can be appended. (A table joined by ref is likely to become the root of another pushed join.)

      If the query optimizer decides on Using join cache for a candidate child table, that table cannot be pushed as a child. However, it may be the root of another set of pushed tables.

    5. Joins referencing tables explicitly partitioned by [LINEAR] HASH, LIST, or RANGE currently cannot be pushed down.

    You can see whether a given join can be pushed down by checking it with EXPLAIN; when the join can be pushed down, you can see references to the pushed join in the Extra column of the output, as shown in this example:

    mysql> EXPLAIN
        ->     SELECT e.first_name, e.last_name, t.title, d.dept_name
        ->         FROM employees e
        ->         JOIN dept_emp de ON e.emp_no=de.emp_no
        ->         JOIN departments d ON d.dept_no=de.dept_no
        ->         JOIN titles t ON e.emp_no=t.emp_no\G
    *************************** 1. row ***************************
               id: 1
      select_type: SIMPLE
            table: d
             type: ALL
    possible_keys: PRIMARY
              key: NULL
          key_len: NULL
              ref: NULL
             rows: 9
            Extra: Parent of 4 pushed join@1
    *************************** 2. row ***************************
               id: 1
      select_type: SIMPLE
            table: de
             type: ref
    possible_keys: PRIMARY,emp_no,dept_no
              key: dept_no
          key_len: 4
              ref: employees.d.dept_no
             rows: 5305
            Extra: Child of 'd' in pushed join@1
    *************************** 3. row ***************************
               id: 1
      select_type: SIMPLE
            table: e
             type: eq_ref
    possible_keys: PRIMARY
              key: PRIMARY
          key_len: 4
              ref: employees.de.emp_no
             rows: 1
            Extra: Child of 'de' in pushed join@1
    *************************** 4. row ***************************
               id: 1
      select_type: SIMPLE
            table: t
             type: ref
    possible_keys: PRIMARY,emp_no
              key: emp_no
          key_len: 4
              ref: employees.de.emp_no
             rows: 19
            Extra: Child of 'e' in pushed join@1
    4 rows in set (0.00 sec)
    Note

    If inner joined child tables are joined by ref, and the result is ordered or grouped by a sorted index, this index cannot provide sorted rows, which forces writing to a sorted tempfile.

    Two additional sources of information about pushed join performance are available:

    1. The status variables Ndb_pushed_queries_defined, Ndb_pushed_queries_dropped, Ndb_pushed_queries_executed, and Ndb_pushed_reads.

    2. The counters in the ndbinfo.counters table that belong to the DBSPJ kernel block. See Section 7.10.10, “The ndbinfo counters Table”, for information about these counters. See also The DBSPJ Block, in the NDB Cluster API Developer Guide.

  • ndb_log_apply_status

    Table 5.244 Type and value information for ndb_log_apply_status

    Property Value
    Name ndb_log_apply_status
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic No
    Type
    Default, Range OFF (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Whether or not a MySQL server acting as a slave logs mysql.ndb_apply_status updates received from its immediate master in its own binary log, using its own server ID


    A read-only variable which shows whether the server was started with the --ndb-log-apply-status option.

  • ndb_log_bin

    Table 5.245 Type and value information for ndb_log_bin

    Property Value
    Name ndb_log_bin
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File No
    Scope Both
    Dynamic Yes
    Type
    Default, Range ON (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Write updates to NDB tables in the binary log. Effective only if binary logging is enabled with --log-bin.


    Causes updates to NDB tables to be written to the binary log. Setting this variable has no effect if binary logging is not already enabled for the server using log_bin. ndb_log_bin defaults to 1 (ON); normally, there is never any need to change this value in a production environment.

  • ndb_log_binlog_index

    Table 5.246 Type and value information for ndb_log_binlog_index

    Property Value
    Name ndb_log_binlog_index
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File No
    Scope Global
    Dynamic Yes
    Type
    Default, Range ON (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Insert mapping between epochs and binary log positions into the ndb_binlog_index table. Defaults to ON. Effective only if binary logging is enabled on the server.


    Causes a mapping of epochs to positions in the binary log to be inserted into the ndb_binlog_index table. Setting this variable has no effect if binary logging is not already enabled for the server using log_bin. (In addition, ndb_log_bin must not be disabled.) ndb_log_binlog_index defaults to 1 (ON); normally, there is never any need to change this value in a production environment.

  • ndb_log_empty_epochs

    Table 5.247 Type and value information for ndb_log_empty_epochs

    Property Value
    Name ndb_log_empty_epochs
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range OFF (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: When enabled, epochs in which there were no changes are written to the ndb_apply_status and ndb_binlog_index tables, even when log_slave_updates is enabled


    When this variable is set to 0, epoch transactions with no changes are not written to the binary log, although a row is still written even for an empty epoch in ndb_binlog_index.

  • ndb_log_empty_update

    Table 5.248 Type and value information for ndb_log_empty_update

    Property Value
    Name ndb_log_empty_update
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range OFF (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: When enabled, updates which produce no changes are written to the ndb_apply_status and ndb_binlog_index tables, even when log_slave_updates is enabled


    When this variable is set to ON (1), update transactions with no changes are written to the binary log, even when --log-slave-updates is enabled.

  • ndb_log_exclusive_reads

    Table 5.249 Type and value information for ndb_log_exclusive_reads

    Property Value
    Name ndb_log_exclusive_reads
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Both
    Dynamic Yes
    Type
    Default, Range 0 (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Log primary key reads with exclusive locks; allow conflict resolution based on read conflicts


    This variable determines whether primary key reads are logged with exclusive locks, which allows for NDB Cluster Replication conflict detection and resolution based on read conflicts. To enable these locks, set the value of ndb_log_exclusive_reads to 1. 0, which disables such locking, is the default.

    For more information, see Read conflict detection and resolution.

  • ndb_log_orig

    Table 5.250 Type and value information for ndb_log_orig

    Property Value
    Name ndb_log_orig
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic No
    Type
    Default, Range OFF (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Whether the id and epoch of the originating server are recorded in the mysql.ndb_binlog_index table. Set using the --ndb-log-orig option when starting mysqld.


    Shows whether the originating server ID and epoch are logged in the ndb_binlog_index table. Set using the --ndb-log-orig server option.

  • ndb_log_transaction_id

    Table 5.251 Type and value information for ndb_log_transaction_id

    Property Value
    Name ndb_log_transaction_id
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Global
    Dynamic No
    Type
    Default, Range OFF (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Whether NDB transaction IDs are written into the binary log (Read-only.)


    This read-only, Boolean system variable shows whether a slave mysqld writes NDB transaction IDs in the binary log (required to use active-active NDB Cluster Replication with NDB$EPOCH_TRANS() conflict detection). To change the setting, use the --ndb-log-transaction-id option.

    ndb_log_transaction_id is not supported in mainline MySQL Server 5.7.

    For more information, see Section 8.11, “NDB Cluster Replication Conflict Resolution”.

  • ndb_optimized_node_selection

    Table 5.252 Type and value information for ndb_optimized_node_selection

    Property Value
    Name ndb_optimized_node_selection
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic No
    Type
    Default, Range ON (Version: NDB 7.5-7.6)
    Default, Range 3 / 0 - 3 (Version: 5.1.22-ndb-6.3.4)
    Notes

    DESCRIPTION: Determines how an SQL node chooses a cluster data node to use as transaction coordinator


    There are two forms of optimized node selection, described here:

    1. The SQL node uses promixity to determine the transaction coordinator; that is, the closest data node to the SQL node is chosen as the transaction coordinator. For this purpose, a data node having a shared memory connection with the SQL node is considered to be closest to the SQL node; the next closest (in order of decreasing proximity) are: TCP connection to localhost; SCI connection; TCP connection from a host other than localhost.

    2. The SQL thread uses distribution awareness to select the data node. That is, the data node housing the cluster partition accessed by the first statement of a given transaction is used as the transaction coordinator for the entire transaction. (This is effective only if the first statement of the transaction accesses no more than one cluster partition.)

    This option takes one of the integer values 0, 1, 2, or 3. 3 is the default. These values affect node selection as follows:

    • 0: Node selection is not optimized. Each data node is employed as the transaction coordinator 8 times before the SQL thread proceeds to the next data node.

    • 1: Proximity to the SQL node is used to determine the transaction coordinator.

    • 2: Distribution awareness is used to select the transaction coordinator. However, if the first statement of the transaction accesses more than one cluster partition, the SQL node reverts to the round-robin behavior seen when this option is set to 0.

    • 3: If distribution awareness can be employed to determine the transaction coordinator, then it is used; otherwise proximity is used to select the transaction coordinator. (This is the default behavior.)

    Proximity is determined as follows:

    1. Start with the value set for the Group parameter (default 55).

    2. For an API node sharing the same host with other API nodes, decrement the value by 1. Assuming the default value for Group, the effective value for data nodes on same host as the API node is 54, and for remote data nodes 55.

    3. (NDB 7.5.2 and later:) Setting ndb_data_node_neighbour further decreases the effective Group value by 50, causing this node to be regarded as the nearest node. This is needed only when all data nodes are on hosts other than that hosts the API node and it is desirable to dedicate one of them to the API node. In normal cases, the default adjustment described previously is sufficient.

    Frequent changes in ndb_data_node_neighbour are not advisable, since this changes the state of the cluster connection and thus may disrupt the selection algorithm for new transactions from each thread until it stablilizes.

  • ndb_read_backup

    Table 5.253 Type and value information for ndb_read_backup

    Property Value
    Name ndb_read_backup
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range OFF (Version: 5.7.12-ndb-7.5.2)
    Notes

    DESCRIPTION: Enable read from any replica


    Enable read from any replica for any NDB table subsequently created.

    Added in NDB 7.5.2.

  • ndb_recv_thread_activation_threshold

    Table 5.254 Type and value information for ndb_recv_thread_activation_threshold

    Property Value
    Name ndb_recv_thread_activation_threshold
    Command Line No
    System Variable No
    Status Variable No
    Option File No
    Scope
    Dynamic No
    Type
    Default, Range 8 / 0 (MIN_ACTIVATION_THRESHOLD) - 16 (MAX_ACTIVATION_THRESHOLD) (Version: 5.6.10-ndb-7.3.1)
    Notes

    DESCRIPTION: Activation threshold when receive thread takes over the polling of the cluster connection (measured in concurrently active threads)


    When this number of concurrently active threads is reached, the receive thread takes over polling of the cluster connection.

    This variable is global in scope. It can also be set on startup using the --ndb-recv-thread-activation-threshold option.

  • ndb_recv_thread_cpu_mask

    Table 5.255 Type and value information for ndb_recv_thread_cpu_mask

    Property Value
    Name ndb_recv_thread_cpu_mask
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Global
    Dynamic Yes
    Type
    Default, Range [empty] (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: CPU mask for locking receiver threads to specific CPUs; specified as hexadecimal. See documentation for details.


    CPU mask for locking receiver threads to specific CPUs. This is specified as a hexadecimal bitmask; for example, 0x33 means that one CPU is used per receiver thread. An empty string is the default; setting ndb_recv_thread_cpu_mask to this value removes any receiver thread locks previously set.

    This variable is global in scope. It can also be set on startup using the --ndb-recv-thread-cpu-mask option.

  • ndb_report_thresh_binlog_epoch_slip

    Table 5.256 Type and value information for ndb_report_thresh_binlog_epoch_slip

    Property Value
    Name ndb_report_thresh_binlog_epoch_slip
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range 3 / 0 - 256 (Version: NDB 7.5-7.6)
    Default, Range 10 / 0 - 256 (Version: 5.7.16-ndb-7.5.4)
    Notes

    DESCRIPTION: NDB 7.5.4 and later: Threshold for number of epochs completely buffered, but not yet consumed by binlog injector thread which when exceeded generates BUFFERED_EPOCHS_OVER_THRESHOLD event buffer status message; prior to NDB 7.5.4: Threshold for number of epochs to lag behind before reporting binary log status


    In NDB 7.5.4 and later, this represents the threshold for the number of epochs completely buffered in the event buffer, but not yet consumed by the binlog injector thread. When this degree of slippage (lag) is exceeded, an event buffer status message is reported, with BUFFERED_EPOCHS_OVER_THRESHOLD supplied as the reason (see Section 7.7.3, “Event Buffer Reporting in the Cluster Log”). Slip is increased when an epoch is received from data nodes and buffered completely in the event buffer; it is decreased when an epoch is consumed by the binlog injector thread, it is reduced. Empty epochs are buffered and queued, and so included in this calculation only when this is enabled using the Ndb::setEventBufferQueueEmptyEpoch() method from the NDB API.

    Prior to NDB 7.5.4, the value of this vairable served as a threshold for the number of epochs to be behind before reporting binary log status. In these previous releases, a value of 3—the default—means that if the difference between which epoch has been received from the storage nodes and which epoch has been applied to the binary log is 3 or more, a status message is then sent to the cluster log.

  • ndb_report_thresh_binlog_mem_usage

    Table 5.257 Type and value information for ndb_report_thresh_binlog_mem_usage

    Property Value
    Name ndb_report_thresh_binlog_mem_usage
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type boolean
    Default, Range 1 / 0 - 1 (Version: NDB 7.6.8)
    Notes

    DESCRIPTION: This is a threshold on the percentage of free memory remaining before reporting binary log status


    This is a threshold on the percentage of free memory remaining before reporting binary log status. For example, a value of 10 (the default) means that if the amount of available memory for receiving binary log data from the data nodes falls below 10%, a status message is sent to the cluster log.

  • ndb_row_checksum

    Table 5.258 Type and value information for ndb_row_checksum

    Property Value
    Name ndb_row_checksum
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type boolean
    Default, Range 1 / 0 - 1 (Version: NDB 7.6.8)
    Notes

    DESCRIPTION: When enabled, set row checksums; enabled by default


    Traditionally, NDB has created tables with row checksums, which checks for hardware issues at the expense of performance. Setting ndb_row_checksum to 0 means that row checksums are not used for new or altered tables, which has a significant impact on performance for all types of queries. This variable is set to 1 by default, to provide backward-compatible behavior.

  • slave_allow_batching

    Table 5.259 Type and value information for slave_allow_batching

    Property Value
    Name slave_allow_batching
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range off (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Turns update batching on and off for a replication slave


    Whether or not batched updates are enabled on NDB Cluster replication slaves.

    Setting this variable has an effect only when using replication with the NDB storage engine; in MySQL Server 5.7, it is present but does nothing. For more information, see Section 8.6, “Starting NDB Cluster Replication (Single Replication Channel)”.

  • ndb_show_foreign_key_mock_tables

    Table 5.260 Type and value information for ndb_show_foreign_key_mock_tables

    Property Value
    Name ndb_show_foreign_key_mock_tables
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range OFF (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Show the mock tables used to support foreign_key_checks=0


    Show the mock tables used by NDB to support foreign_key_checks=0. When this is enabled, extra warnings are shown when creating and dropping the tables. The real (internal) name of the table can be seen in the output of SHOW CREATE TABLE.

  • ndb_slave_conflict_role

    Table 5.261 Type and value information for ndb_slave_conflict_role

    Property Value
    Name ndb_slave_conflict_role
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic Yes
    Type
    Default, Range NONE / NONE, PRIMARY, SECONDARY, PASS (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Role for slave to play in conflict detection and resolution. Value is one of PRIMARY, SECONDARY, PASS, or NONE (default). Can be changed only when slave SQL thread is stopped. See documentation for further information.


    Determine the role of this SQL node (and NDB Cluster) in a circular (active-active) replication setup. ndb_slave_conflict_role can take any one of the values PRIMARY, SECONDARY, PASS, or NULL (the default). The slave SQL thread must be stopped before you can change ndb_slave_conflict_role. In addition, it is not possible to change directly between PASS and either of PRIMARY or SECONDARY directly; in such cases, you must ensure that the SQL thread is stopped, then execute SET @@GLOBAL.ndb_slave_conflict_role = 'NONE' first.

    For more information, see Section 8.11, “NDB Cluster Replication Conflict Resolution”.

  • ndb_table_no_logging

    Table 5.262 Type and value information for ndb_table_no_logging

    Property Value
    Name ndb_table_no_logging
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Session
    Dynamic Yes
    Type
    Default, Range FALSE (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: NDB tables created when this setting is enabled are not checkpointed to disk (although table schema files are created). The setting in effect when the table is created with or altered to use NDBCLUSTER persists for the lifetime of the table.


    When this variable is set to ON or 1, it causes NDB tables not to be checkpointed to disk. More specifically, this setting applies to tables which are created or altered using ENGINE NDB when ndb_table_no_logging is enabled, and continues to apply for the lifetime of the table, even if ndb_table_no_logging is later changed. Suppose that A, B, C, and D are tables that we create (and perhaps also alter), and that we also change the setting for ndb_table_no_logging as shown here:

    SET @@ndb_table_no_logging = 1;
    CREATE TABLE A ... ENGINE NDB;
    CREATE TABLE B ... ENGINE MYISAM;
    CREATE TABLE C ... ENGINE MYISAM;
    ALTER TABLE B ENGINE NDB;
    SET @@ndb_table_no_logging = 0;
    CREATE TABLE D ... ENGINE NDB;
    ALTER TABLE C ENGINE NDB;
    SET @@ndb_table_no_logging = 1;

    After the previous sequence of events, tables A and B are not checkpointed; A was created with ENGINE NDB and B was altered to use NDB, both while ndb_table_no_logging was enabled. However, tables C and D are logged; C was altered to use NDB and D was created using ENGINE NDB, both while ndb_table_no_logging was disabled. Setting ndb_table_no_logging back to 1 or ON does not cause table C or D to be checkpointed.

    Note

    ndb_table_no_logging has no effect on the creation of NDB table schema files; to suppress these, use ndb_table_temporary instead.

  • ndb_table_temporary

    Table 5.263 Type and value information for ndb_table_temporary

    Property Value
    Name ndb_table_temporary
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Session
    Dynamic Yes
    Type
    Default, Range FALSE (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: NDB tables are not persistent on disk: no schema files are created and the tables are not logged


    When set to ON or 1, this variable causes NDB tables not to be written to disk: This means that no table schema files are created, and that the tables are not logged.

    Note

    Setting this variable currently has no effect. This is a known issue; see Bug #34036.

  • ndb_use_copying_alter_table

    Table 5.264 Type and value information for ndb_use_copying_alter_table

    Property Value
    Name ndb_use_copying_alter_table
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Both
    Dynamic No
    Type
    Notes

    DESCRIPTION: Use copying ALTER TABLE operations in NDB Cluster


    Forces NDB to use copying of tables in the event of problems with online ALTER TABLE operations. The default value is OFF.

  • ndb_use_exact_count

    Table 5.265 Type and value information for ndb_use_exact_count

    Property Value
    Name ndb_use_exact_count
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Both
    Dynamic Yes
    Type
    Default, Range ON (Version: NDB 7.5-7.6)
    Default, Range OFF (Version: 5.1.47-ndb-7.1.8)
    Notes

    DESCRIPTION: Use exact row count when planning queries


    Forces NDB to use a count of records during SELECT COUNT(*) query planning to speed up this type of query. The default value is OFF, which allows for faster queries overall.

  • ndb_use_transactions

    Table 5.266 Type and value information for ndb_use_transactions

    Property Value
    Name ndb_use_transactions
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Both
    Dynamic Yes
    Type
    Default, Range ON (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Forces NDB to use a count of records during SELECT COUNT(*) query planning to speed up this type of query


    You can disable NDB transaction support by setting this variable's values to OFF (not recommended). The default is ON.

  • ndb_version

    Table 5.267 Type and value information for ndb_version

    Property Value
    Name ndb_version
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Global
    Dynamic No
    Type
    Default, Range (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Shows build and NDB engine version as an integer


    NDB engine version, as a composite integer.

  • ndb_version_string

    Table 5.268 Type and value information for ndb_version_string

    Property Value
    Name ndb_version_string
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Global
    Dynamic No
    Type
    Default, Range (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Shows build information including NDB engine version in ndb-x.y.z format


    NDB engine version in ndb-x.y.z format.

  • server_id_bits

    Table 5.269 Type and value information for server_id_bits

    Property Value
    Name server_id_bits
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File Yes
    Scope Global
    Dynamic No
    Type
    Default, Range 32 / 7 - 32 (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: The effective value of server_id if the server was started with the --server-id-bits option set to a nondefault value


    The effective value of server_id if the server was started with the --server-id-bits option set to a nondefault value.

    If the value of server_id greater than or equal to 2 to the power of server_id_bits, mysqld refuses to start.

    This system variable is supported only by NDB Cluster. server_id_bits is not supported by the standard MySQL Server.

  • transaction_allow_batching

    Table 5.270 Type and value information for transaction_allow_batching

    Property Value
    Name transaction_allow_batching
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Session
    Dynamic Yes
    Type
    Default, Range FALSE (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Allows batching of statements within a transaction. Disable AUTOCOMMIT to use.


    When set to 1 or ON, this variable enables batching of statements within the same transaction. To use this variable, autocommit must first be disabled by setting it to 0 or OFF; otherwise, setting transaction_allow_batching has no effect.

    It is safe to use this variable with transactions that performs writes only, as having it enabled can lead to reads from the before image. You should ensure that any pending transactions are committed (using an explicit COMMIT if desired) before issuing a SELECT.

    Important

    transaction_allow_batching should not be used whenever there is the possibility that the effects of a given statement depend on the outcome of a previous statement within the same transaction.

    This variable is currently supported for NDB Cluster only.

The system variables in the following list all relate to the ndbinfo information database.

  • ndbinfo_database

    Table 5.271 Type and value information for ndbinfo_database

    Property Value
    Name ndbinfo_database
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Global
    Dynamic No
    Type
    Default, Range ndbinfo (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: The name used for the NDB information database; read only


    Shows the name used for the NDB information database; the default is ndbinfo. This is a read-only variable whose value is determined at compile time; you can set it by starting the server using --ndbinfo-database=name, which sets the value shown for this variable but does not actually change the name used for the NDB information database.

  • ndbinfo_max_bytes

    Table 5.272 Type and value information for ndbinfo_max_bytes

    Property Value
    Name ndbinfo_max_bytes
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File No
    Scope Both
    Dynamic Yes
    Type
    Default, Range 0 / - (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Used for debugging only


    Used in testing and debugging only.

  • ndbinfo_max_rows

    Table 5.273 Type and value information for ndbinfo_max_rows

    Property Value
    Name ndbinfo_max_rows
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File No
    Scope Both
    Dynamic Yes
    Type
    Default, Range 10 / - (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Used for debugging only


    Used in testing and debugging only.

  • ndbinfo_offline

    Table 5.274 Type and value information for ndbinfo_offline

    Property Value
    Name ndbinfo_offline
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Global
    Dynamic Yes
    Type
    Default, Range OFF (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Put the ndbinfo database into offline mode, in which no rows are returned from tables or views


    Place the ndbinfo database into offline mode, in which tables and views can be opened even when they do not actually exist, or when they exist but have different definitions in NDB. No rows are returned from such tables (or views).

  • ndbinfo_show_hidden

    Table 5.275 Type and value information for ndbinfo_show_hidden

    Property Value
    Name ndbinfo_show_hidden
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File No
    Scope Both
    Dynamic Yes
    Type
    Default, Range OFF (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: Whether to show ndbinfo internal base tables in the mysql client. The default is OFF.


    Whether or not the ndbinfo database's underlying internal tables are shown in the mysql client. The default is OFF.

  • ndbinfo_table_prefix

    Table 5.276 Type and value information for ndbinfo_table_prefix

    Property Value
    Name ndbinfo_table_prefix
    Command Line Yes
    System Variable Yes
    Status Variable No
    Option File No
    Scope Both
    Dynamic Yes
    Type
    Default, Range ndb$ (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: The prefix to use for naming ndbinfo internal base tables


    The prefix used in naming the ndbinfo database's base tables (normally hidden, unless exposed by setting ndbinfo_show_hidden). This is a read-only variable whose default value is ndb$. You can start the server with the --ndbinfo-table-prefix option, but this merely sets the variable and does not change the actual prefix used to name the hidden base tables; the prefix itself is determined at compile time.

  • ndbinfo_version

    Table 5.277 Type and value information for ndbinfo_version

    Property Value
    Name ndbinfo_version
    Command Line No
    System Variable Yes
    Status Variable No
    Option File No
    Scope Global
    Dynamic No
    Type
    Default, Range (Version: NDB 7.5-7.6)
    Notes

    DESCRIPTION: The version of the ndbinfo engine; read only


    Shows the version of the ndbinfo engine in use; read-only.


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