--ndbcluster

The NDBCLUSTER storage engine is necessary for using NDB Cluster. If a mysqld binary includes support for the NDBCLUSTER storage engine, the engine is disabled by default. Use the --ndbcluster option to enable it. Use --skip-ndbcluster to explicitly disable the engine.

The --ndbcluster option is ignored (and the NDB storage engine is not enabled) if --initialize is also used. (It is neither necessary nor desirable to use this option together with --initialize.)

--ndb-allow-copying-alter-table=[ON|OFF]

Let ALTER TABLE and other DDL statements use copying operations on NDB tables. Set to OFF to keep this from happening; doing so may improve performance of critical applications.

--ndb-applier-allow-skip-epoch

Use together with --replica-skip-errors to cause NDB to ignore skipped epoch transactions. Has no effect when used alone.

--ndb-batch-size=#

This sets the size in bytes that is used for NDB transaction batches.

--ndb-cluster-connection-pool=#

By setting this option to a value greater than 1 (the default), a mysqld process can use multiple connections to the cluster, effectively mimicking several SQL nodes. Each connection requires its own [api] or [mysqld] section in the cluster configuration (config.ini) file, and counts against the maximum number of API connections supported by the cluster.

Suppose that you have 2 cluster host computers, each running an SQL node whose mysqld process was started with --ndb-cluster-connection-pool=4; this means that the cluster must have 8 API slots available for these connections (instead of 2). All of these connections are set up when the SQL node connects to the cluster, and are allocated to threads in a round-robin fashion.

This option is useful only when running mysqld on host machines having multiple CPUs, multiple cores, or both. For best results, the value should be smaller than the total number of cores available on the host machine. Setting it to a value greater than this is likely to degrade performance severely.

--ndb-cluster-connection-pool-nodeids=list

Specifies a comma-separated list of node IDs for connections to the cluster used by an SQL node. The number of nodes in this list must be the same as the value set for the --ndb-cluster-connection-pool option.

--ndb-blob-read-batch-bytes=bytes

This option can be used to set the size (in bytes) for batching of BLOB data reads in NDB Cluster applications. When this batch size is exceeded by the amount of BLOB data to be read within the current transaction, any pending BLOB read operations are immediately executed.

The maximum value for this option is 4294967295; the default is 65536. Setting it to 0 has the effect of disabling BLOB read batching.

--ndb-blob-write-batch-bytes=bytes

This option can be used to set the size (in bytes) for batching of BLOB data writes in NDB Cluster applications. When this batch size is exceeded by the amount of BLOB data to be written within the current transaction, any pending BLOB write operations are immediately executed.

The maximum value for this option is 4294967295; the default is 65536. Setting it to 0 has the effect of disabling BLOB write batching.

--ndb-connectstring=connection_string

When using the NDBCLUSTER storage engine, this option specifies the management server that distributes cluster configuration data. See Section 25.4.3.3, “NDB Cluster Connection Strings”, for syntax.

--ndb-default-column-format=[FIXED|DYNAMIC]

Sets the default COLUMN_FORMAT and ROW_FORMAT for new tables (see Section 15.1.20, “CREATE TABLE Statement”). The default is FIXED.

--ndb-deferred-constraints=[0|1]

Controls whether or not constraint checks on unique indexes are deferred until commit time, where such checks are supported. 0 is the default.

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

--ndb-schema-dist-timeout=#

Specifies the maximum time in seconds that this mysqld waits for a schema operation to complete before marking it as having timed out.

--ndb-distribution=[KEYHASH|LINHASH]

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-log-apply-status

Causes a replica mysqld to log any updates received from its immediate source to the mysql.ndb_apply_status table in its own binary log using its own server ID rather than the server ID of the source. In a circular or chain replication setting, this allows such updates to propagate to the mysql.ndb_apply_status tables of any MySQL servers configured as replicas of the current mysqld.

In a chain replication setup, using this option allows downstream (replica) clusters to be aware of their positions relative to all of their upstream contributors (sourcess).

In a circular replication setup, this option causes changes to ndb_apply_status tables to complete the entire circuit, eventually propagating back to the originating NDB Cluster. This also allows a cluster acting as a replication source to see when its changes (epochs) have been applied to the other clusters in the circle.

This option has no effect unless the MySQL server is started with the --ndbcluster option.

--ndb-log-empty-epochs=[ON|OFF]

Causes epochs during which there were no changes to be written to the ndb_apply_status and ndb_binlog_index tables, even when log_replica_updates is enabled.

By default this option is disabled. Disabling --ndb-log-empty-epochs causes epoch transactions with no changes not to be written to the binary log, although a row is still written even for an empty epoch in ndb_binlog_index.

Because --ndb-log-empty-epochs=1 causes the size of the ndb_binlog_index table to increase independently of the size of the binary log, users should be prepared to manage the growth of this table, even if they expect the cluster to be idle a large part of the time.

--ndb-log-empty-update=[ON|OFF]

Causes updates that produced no changes to be written to the ndb_apply_status and ndb_binlog_index tables, even when log_replica_updates is enabled.

By default this option is disabled (OFF). Disabling --ndb-log-empty-update causes updates with no changes not to be written to the binary log.

--ndb-log-exclusive-reads=[0|1]

Starting the server with this option causes primary key reads to be logged with exclusive locks, which allows for NDB Cluster Replication conflict detection and resolution based on read conflicts. You can also enable and disable these locks at runtime by setting the value of the ndb_log_exclusive_reads system variable to 1 or 0, respectively. 0 (disable locking) is the default.

For more information, see Read conflict detection and resolution.

--ndb-log-fail-terminate

When this option is specified, and complete logging of all found row events is not possible, the mysqld process is terminated.

--ndb-log-orig

Log the originating server ID and epoch in the ndb_binlog_index table.

For more information, see Section 25.7.4, “NDB Cluster Replication Schema and Tables”.

--ndb-log-transaction-dependency

Causes the NDB binary logging thread to calculate transaction dependencies for each transaction which it writes to the binary log. The default value is FALSE.

This option cannot be set at runtime; the corresponding ndb_log_transaction_dependency system variable is read-only.

--ndb-log-transaction-id

Causes a replica mysqld to write the NDB transaction ID in each row of the binary log. The default value is FALSE.

--ndb-log-transaction-id is required to enable NDB Cluster Replication conflict detection and resolution using the NDB$EPOCH_TRANS() function (see NDB$EPOCH_TRANS()). For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

--ndb-log-update-as-write

Whether updates on the source are written to the binary log as updates (OFF) or writes (ON). When this option is enabled, and both --ndb-log-updated-only and --ndb-log-update-minimal are disabled, operations of different types are loǵged as described in the following list:

This option can be used for NDB Replication conflict resolution in combination with the other two NDB logging options mentioned previously; see ndb_replication Table, for more information.

--ndb-log-updated-only

Whether mysqld writes updates only (ON) or complete rows (OFF) to the binary log. When this option is enabled, and both --ndb-log-update-as-write and --ndb-log-update-minimal are disabled, operations of different types are loǵged as described in the following list:

This option can be used for NDB Replication conflict resolution in combination with the other two NDB logging options mentioned previously; see ndb_replication Table, for more information about how these options interact with one another.

--ndb-log-update-minimal

Log updates in a minimal fashion, by writing only the primary key values in the before image, and only the changed columns in the after image. This may cause compatibility problems if replicating to storage engines other than NDB. When this option is enabled, and both --ndb-log-updated-only and --ndb-log-update-as-write are disabled, operations of different types are loǵged as described in the following list:

This option can be used for NDB Replication conflict resolution in combination with the other two NDB logging options mentioned previously; see ndb_replication Table, for more information.

--ndb-mgm-tls=[relaxed|strict]

Sets the level of TLS support required for TLS connections to NDB Cluster; the value is one of relaxed or strict. relaxed means that a TLS connection is attempted, but success is not required; strict means that TLS is required to connect. The default is relaxed.

--ndb-mgmd-host=host[:port]

Can be used to set the host and port number of a single management server for the program to connect to. If the program requires node IDs or references to multiple management servers (or both) in its connection information, use the --ndb-connectstring option instead.

--ndb-nodeid=#

Set this MySQL server's node ID in an NDB Cluster.

The --ndb-nodeid option overrides any node ID set with --ndb-connectstring, regardless of the order in which the two options are used.

In addition, if --ndb-nodeid is used, then either a matching node ID must be found in a [mysqld] or [api] section of config.ini, or there must be an “open” [mysqld] or [api] section in the file (that is, a section without a NodeId or Id parameter specified). This is also true if the node ID is specified as part of the connection string.

Regardless of how the node ID is determined, it is shown as the value of the global status variable Ndb_cluster_node_id in the output of SHOW STATUS, and as cluster_node_id in the connection row of the output of SHOW ENGINE NDBCLUSTER STATUS.

For more information about node IDs for NDB Cluster SQL nodes, see Section 25.4.3.7, “Defining SQL and Other API Nodes in an NDB Cluster”.

--ndbinfo={ON|OFF|FORCE}

Enables the plugin for the ndbinfo information database. By default this is ON whenever NDBCLUSTER is enabled.

--ndb-optimization-delay=milliseconds

Set the number of milliseconds to wait between sets of rows by OPTIMIZE TABLE statements on NDB tables. The default is 10.

--ndb-optimized-node-selection

Enable optimizations for selection of nodes for transactions. Enabled by default; use --skip-ndb-optimized-node-selection to disable.

ndb-tls-search-path=path

List of directories to search for CAs and private keys for NDB TLS connections. The list is comma-delimited on Unix platforms and semicolon-delimited on Windows.

--ndb-transid-mysql-connection-map=state

Enables or disables the plugin that handles the ndb_transid_mysql_connection_map table in the INFORMATION_SCHEMA database. Takes one of the values ON, OFF, or FORCE. ON (the default) enables the plugin. OFF disables the plugin, which makes ndb_transid_mysql_connection_map inaccessible. FORCE keeps the MySQL Server from starting if the plugin fails to load and start.

You can see whether the ndb_transid_mysql_connection_map table plugin is running by checking the output of SHOW PLUGINS.

--ndb-wait-connected=seconds

This option sets the period of time that the MySQL server waits for connections to NDB Cluster management and data nodes to be established before accepting MySQL client connections. The time is specified in seconds. The default value is 30.

--ndb-wait-setup=seconds

This variable shows the period of time that the MySQL server waits for the NDB storage engine to complete setup before timing out and treating NDB as unavailable. The time is specified in seconds. The default value is 30.

--skip-ndbcluster

Disable the NDBCLUSTER storage engine. This is the default for binaries that were built with NDBCLUSTER storage engine support; the server allocates memory and other resources for this storage engine only if the --ndbcluster option is given explicitly. See Section 25.4.1, “Quick Test Setup of NDB Cluster”, for an example.

ndb_autoincrement_prefetch_sz

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 of consecutive autoincrement numbers being used in a batch of inserts.

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.

ndb_clear_apply_status

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

ndb_conflict_role

Determines the role of this SQL node (and NDB Cluster) in a circular (“active-active”) replication setup. ndb_conflict_role can take any one of the values PRIMARY, SECONDARY, PASS, or NULL (the default). The replica SQL thread must be stopped before you can change ndb_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_conflict_role = 'NONE' first.

This variable replaces the deprecated ndb_slave_conflict_role.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

ndb_data_node_neighbour

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 Section 15.1.20.12, “Setting NDB Comment Options”, for further information.

ndb_dbg_check_shares

When set to 1, check that no shares are lingering. Available in debug builds only.

ndb_default_column_format

Sets the default COLUMN_FORMAT and ROW_FORMAT for new tables (see Section 15.1.20, “CREATE TABLE Statement”). The default is FIXED.

ndb_deferred_constraints

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

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

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

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

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

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

ndb_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 Section 15.1.20.12, “Setting NDB Comment Options”, for syntax and other information.

ndb_index_stat_enable

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

The index statistics tables are always created when the server starts, regardless of this option's value.

ndb_index_stat_option

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.

ndb_join_pushdown

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:

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)

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

ndb_log_apply_status

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

ndb_log_bin

Causes updates to NDB tables to be written to the binary log. The setting for this variable has no effect if binary logging is not already enabled on the server using log_bin. ndb_log_bin defaults to 0 (FALSE).

ndb_log_binlog_index

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_cache_size

Set the size of the transaction cache used for writing the NDB binary log.

ndb_log_empty_epochs

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

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

ndb_log_exclusive_reads

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

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

This read-only, Boolean system variable shows whether a replica 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 8.4.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

ndb_log_transaction_compression

Whether a replica mysqld writes compressed transactions in the binary log; present only if mysqld was compiled with support for NDB.

You should note that starting the MySQL server with --binlog-transaction-compression forces this variable to be enabled (ON), and that this overrides any setting for --ndb-log-transaction-compression made on the command line or in a my.cnf file, as shown here:

$> mysqld_safe --ndbcluster --ndb-connectstring=127.0.0.1 \
  --binlog-transaction-compression=ON --ndb-log-transaction-compression=OFF &
[1] 27667
$> 2022-07-07T12:29:20.459937Z mysqld_safe Logging to '/usr/local/mysql/data/myhost.err'.
2022-07-07T12:29:20.509873Z mysqld_safe Starting mysqld daemon with databases from /usr/local/mysql/data

$> mysql -e 'SHOW VARIABLES LIKE "%transaction_compression%"'
+--------------------------------------------+-------+
| Variable_name                              | Value |
+--------------------------------------------+-------+
| binlog_transaction_compression             | ON    |
| binlog_transaction_compression_level_zstd  | 3     |
| ndb_log_transaction_compression            | ON    |
| ndb_log_transaction_compression_level_zstd | 3     |
+--------------------------------------------+-------+

To disable binary log transaction compression for NDB tables only, set the ndb_log_transaction_compression system variable to OFF in a mysql or other client session after starting mysqld.

Setting the binlog_transaction_compression variable after startup has no effect on the value of ndb_log_transaction_compression.

For more information on binary log transaction compression, such as which events are or are not compressed and as well as behavior changes to be aware of when this feature is used, see Section 7.4.4.5, “Binary Log Transaction Compression”.

ndb_log_transaction_compression_level_zstd

The ZSTD compression level used for writing compressed transactions to the replica's binary log if enabled by ndb_log_transaction_compression. Not supported if mysqld was not compiled with support for the NDB storage engine.

See Section 7.4.4.5, “Binary Log Transaction Compression”, for more information.

ndb_metadata_check

NDB uses a background thread to check for metadata changes each ndb_metadata_check_interval seconds as compared with the MySQL data dictionary. This metadata change detection thread can be disabled by setting ndb_metadata_check to OFF. The thread is enabled by default.

ndb_metadata_check_interval

NDB runs a metadata change detection thread in the background to determine when the NDB dictionary has changed with respect to the MySQL data dictionary. By default,the interval between such checks is 60 seconds; this can be adjusted by setting the value of ndb_metadata_check_interval. To enable or disable the thread, use ndb_metadata_check.

ndb_metadata_sync

Setting this variable causes the change monitor thread to override any values set for ndb_metadata_check or ndb_metadata_check_interval, and to enter a period of continuous change detection. When the thread ascertains that there are no more changes to be detected, it stalls until the binary logging thread has finished synchronization of all detected objects. ndb_metadata_sync is then set to false, and the change monitor thread reverts to the behavior determined by the settings for ndb_metadata_check and ndb_metadata_check_interval.

Setting this variable to true causes the list of excluded objects to be cleared; setting it to false clears the list of objects to be retried.

ndb_optimized_node_selection

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

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

Proximity is determined as follows:

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

Enable read from any fragment replica for any NDB table subsequently created; doing so greatly improves the table read performance at a relatively small cost to writes.

If the SQL node and the data node use the same host name or IP address, this fact is detected automatically, so that the preference is to send reads to the same host. If these nodes are on the same host but use different IP addresses, you can tell the SQL node to use the correct data node by setting the value of ndb_data_node_neighbour on the SQL node to the node ID of the data node.

To enable or disable read from any fragment replica for an individual table, you can set the NDB_TABLE option READ_BACKUP for the table accordingly, in a CREATE TABLE or ALTER TABLE statement; see Section 15.1.20.12, “Setting NDB Comment Options”, for more information.

ndb_recv_thread_activation_threshold

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 at startup.

ndb_recv_thread_cpu_mask

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 at startup.

ndb_report_thresh_binlog_epoch_slip

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 25.6.2.3, “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.

ndb_report_thresh_binlog_mem_usage

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

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.

ndb_schema_dist_lock_wait_timeout

Number of seconds to wait during schema distribution for the metadata lock taken on each SQL node in order to change its local data dictionary to reflect the DDL statement change. After this time has elapsed, a warning is returned to the effect that a given SQL node's data dictionary was not updated with the change. This avoids having the binary logging thread wait an excessive length of time while handling schema operations.

ndb_schema_dist_timeout

Number of seconds to wait before detecting a timeout during schema distribution. This can indicate that other SQL nodes are experiencing excessive activity, or that they are somehow being prevented from acquiring necessary resources at this time.

ndb_schema_dist_upgrade_allowed

Allow upgrading of the schema distribution table when connecting to NDB. When true (the default), this change is deferred until all SQL nodes have been upgraded to the same version of the NDB Cluster software.

ndb_show_foreign_key_mock_tables

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

Deprecated synonym for ndb_conflict_role.

ndb_table_no_logging

When this variable is set to ON or 1, it causes all tables created or altered using ENGINE NDB to be nonlogging; that is, no data changes for this table are written to the redo log or checkpointed to disk, just as if the table had been created or altered using the NOLOGGING option for CREATE TABLE or ALTER TABLE.

For more information about nonlogging NDB tables, see NDB_TABLE Options.

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

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.

ndb_use_copying_alter_table

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

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

You can disable NDB transaction support by setting this variable's value to OFF. This is generally not recommended, although it may be useful to disable transaction support within a given client session when that session is used to import one or more dump files with large transactions; this allows a multi-row insert to be executed in parts, rather than as a single transaction. In such cases, once the import has been completed, you should either reset the variable value for this session to ON, or simply terminate the session.

ndb_version

NDB engine version, as a composite integer.

ndb_version_string

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

replica_allow_batching

Whether or not batched updates are enabled on NDB Cluster replicas.

Allowing batched updates on the replica greatly improves performance, particularly when replicating TEXT, BLOB, and JSON columns. For this reason, replica_allow_batching is enabled by default.

Setting this variable has an effect only when using replication with the NDB storage engine; in MySQL Server 8.4, it is present but does nothing. For more information, see Section 25.7.6, “Starting NDB Cluster Replication (Single Replication Channel)”.

ndb_replica_batch_size

Determines the batch size in bytes used by the replication applier thread. Set this variable rather than the --ndb-batch-size option to apply this setting to the replica, exclusive of any other sessions.

If this variable is unset (default 2 MB), its effective value is the greater of the value of --ndb-batch-size and 2 MB.

ndb_replica_blob_write_batch_bytes

Control the batch write size used for blob data by the replication applier thread.

Use this variable rather than the --ndb-blob-write-batch-bytes option to control the blob batch write size on the replica, exclusive of any other sessions. The reason for this is that, when ndb_replica_blob_write_batch_bytes​is not set,​the effective blob batch size (that is, the maximum number of pending bytes to write for blob columns) is determined by the greater of the value of --ndb-blob-write-batch-bytes and 2 MB (the default for ndb_replica_blob_write_batch_bytes).

Setting ndb_replica_blob_write_batch_bytes to 0 means that NDB imposes no limit on the size of blob batch writes on the replica.

server_id_bits

This variable indicates the number of least significant bits within the 32-bit server_id which actually identify the server. Indicating that the server is actually identified by fewer than 32 bits makes it possible for some of the remaining bits to be used for other purposes, such as storing user data generated by applications using the NDB API's Event API within the AnyValue of an OperationOptions structure (NDB Cluster uses the AnyValue to store the server ID).

When extracting the effective server ID from server_id for purposes such as detection of replication loops, the server ignores the remaining bits. The server_id_bits variable is used to mask out any irrelevant bits of server_id in the I/O and SQL threads when deciding whether an event should be ignored based on the server ID.

This data can be read from the binary log by mysqlbinlog, provided that it is run with its own server_id_bits variable set to 32 (the default).

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

This system variable is supported only by NDB Cluster. It is not supported in the standard MySQL 8.4 Server.

slave_allow_batching

Deprecated synonym for replica_allow_batching.

transaction_allow_batching

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.

This variable is currently supported for NDB Cluster only.

ndbinfo_database

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.

ndbinfo_max_bytes

Used in testing and debugging only.

ndbinfo_max_rows

Used in testing and debugging only.

ndbinfo_offline

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

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

ndbinfo_table_prefix

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$; the prefix itself is determined at compile time.

ndbinfo_version

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

Handler_discover

The MySQL server can ask the NDBCLUSTER storage engine if it knows about a table with a given name. This is called discovery. Handler_discover indicates the number of times that tables have been discovered using this mechanism.

Ndb_api_adaptive_send_deferred_count

Number of adaptive send calls that were not actually sent.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_adaptive_send_deferred_count_session

Number of adaptive send calls that were not actually sent.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_adaptive_send_deferred_count_replica

Number of adaptive send calls that were not actually sent by this replica.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_adaptive_send_deferred_count_slave

Deprecated synonym for Ndb_api_adaptive_send_deferred_count_replica.

Ndb_api_adaptive_send_forced_count

Number of adaptive send calls using forced-send sent by this MySQL Server (SQL node).

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_adaptive_send_forced_count_session

Number of adaptive send calls using forced-send sent in this client session.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_adaptive_send_forced_count_replica

Number of adaptive send calls using forced-send sent by this replica.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_adaptive_send_forced_count_slave

Deprecated synonym for Ndb_api_adaptive_send_forced_count_replica.

Ndb_api_adaptive_send_unforced_count

Number of adaptive send calls without forced-send sent by this MySQL server (SQL node).

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_adaptive_send_unforced_count_session

Number of adaptive send calls without forced-send sent in this client session.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_adaptive_send_unforced_count_replica

Number of adaptive send calls without forced-send sent by this replica.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_adaptive_send_unforced_count_slave

Deprecated synonym for Ndb_api_adaptive_send_unforced_count_replica.

Ndb_api_bytes_sent_count_session

Amount of data (in bytes) sent to the data nodes in this client session.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_bytes_sent_count_replica

Amount of data (in bytes) sent to the data nodes by this replica.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_bytes_sent_count_slave

Deprecated synonym for Ndb_api_bytes_sent_count_replica.

Ndb_api_bytes_sent_count

Amount of data (in bytes) sent to the data nodes by this MySQL Server (SQL node).

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_bytes_received_count_session

Amount of data (in bytes) received from the data nodes in this client session.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_bytes_received_count_replica

Amount of data (in bytes) received from the data nodes by this replica.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_bytes_received_count_slave

Deprecated synonym for Ndb_api_bytes_received_count_replica.

Ndb_api_bytes_received_count

Amount of data (in bytes) received from the data nodes by this MySQL Server (SQL node).

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_event_data_count_injector

The number of row change events received by the NDB binlog injector thread.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_event_data_count

The number of row change events received by this MySQL Server (SQL node).

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_event_nondata_count_injector

The number of events received, other than row change events, by the NDB binary log injector thread.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_event_nondata_count

The number of events received, other than row change events, by this MySQL Server (SQL node).

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_event_bytes_count_injector

The number of bytes of events received by the NDB binlog injector thread.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_event_bytes_count

The number of bytes of events received by this MySQL Server (SQL node).

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_pk_op_count_session

The number of operations in this client session based on or using primary keys. This includes operations on blob tables, implicit unlock operations, and auto-increment operations, as well as user-visible primary key operations.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_pk_op_count_replica

The number of operations by this replica based on or using primary keys. This includes operations on blob tables, implicit unlock operations, and auto-increment operations, as well as user-visible primary key operations.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_pk_op_count_slave

Deprecated synonym for Ndb_api_pk_op_count_replica.

Ndb_api_pk_op_count

The number of operations by this MySQL Server (SQL node) based on or using primary keys. This includes operations on blob tables, implicit unlock operations, and auto-increment operations, as well as user-visible primary key operations.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_pruned_scan_count_session

The number of scans in this client session that have been pruned to a single partition.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_pruned_scan_count_replica

The number of scans by this replica that have been pruned to a single partition.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_pruned_scan_count_slave

Deprecated synonym for Ndb_api_pruned_scan_count_replica.

Ndb_api_pruned_scan_count

The number of scans by this MySQL Server (SQL node) that have been pruned to a single partition.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_range_scan_count_session

The number of range scans that have been started in this client session.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_range_scan_count_replica

The number of range scans that have been started by this replica.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_range_scan_count_slave

Deprecated synonym for Ndb_api_range_scan_count_replica.

Ndb_api_range_scan_count

The number of range scans that have been started by this MySQL Server (SQL node).

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_read_row_count_session

The total number of rows that have been read in this client session. This includes all rows read by any primary key, unique key, or scan operation made in this client session.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_read_row_count_replica

The total number of rows that have been read by this replica. This includes all rows read by any primary key, unique key, or scan operation made by this replica.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_read_row_count_slave

Deprecated synonym for Ndb_api_read_row_count_replica.

Ndb_api_read_row_count

The total number of rows that have been read by this MySQL Server (SQL node). This includes all rows read by any primary key, unique key, or scan operation made by this MySQL Server (SQL node).

You should be aware that this value may not be completely accurate with regard to rows read by SELECT COUNT(*) queries, due to the fact that, in this case, the MySQL server actually reads pseudo-rows in the form [table fragment ID]:[number of rows in fragment] and sums the rows per fragment for all fragments in the table to derive an estimated count for all rows. Ndb_api_read_row_count uses this estimate and not the actual number of rows in the table.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_scan_batch_count_session

The number of batches of rows received in this client session. 1 batch is defined as 1 set of scan results from a single fragment.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_scan_batch_count_replica

The number of batches of rows received by this replica. 1 batch is defined as 1 set of scan results from a single fragment.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_scan_batch_count_slave

Deprecated synonym for Ndb_api_scan_batch_count_replica.

Ndb_api_scan_batch_count

The number of batches of rows received by this MySQL Server (SQL node). 1 batch is defined as 1 set of scan results from a single fragment.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_table_scan_count_session

The number of table scans that have been started in this client session, including scans of internal tables,.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_table_scan_count_replica

The number of table scans that have been started by this replica, including scans of internal tables.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_table_scan_count_slave

Deprecated synonym for Ndb_api_table_scan_count_replica.

Ndb_api_table_scan_count

The number of table scans that have been started by this MySQL Server (SQL node), including scans of internal tables,.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_abort_count_session

The number of transactions aborted in this client session.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_abort_count_replica

The number of transactions aborted by this replica.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_abort_count_slave

Deprecated synonym for Ndb_api_trans_abort_count_replica.

Ndb_api_trans_abort_count

The number of transactions aborted by this MySQL Server (SQL node).

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_close_count_session

The number of transactions closed in this client session. This value may be greater than the sum of Ndb_api_trans_commit_count_session and Ndb_api_trans_abort_count_session, since some transactions may have been rolled back.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_close_count_replica

The number of transactions closed by this replica. This value may be greater than the sum of Ndb_api_trans_commit_count_replica and Ndb_api_trans_abort_count_replica, since some transactions may have been rolled back.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_close_count_slave

Deprecated synonym for Ndb_api_trans_close_count_replica.

Ndb_api_trans_close_count

The number of transactions closed by this MySQL Server (SQL node). This value may be greater than the sum of Ndb_api_trans_commit_count and Ndb_api_trans_abort_count, since some transactions may have been rolled back.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_commit_count_session

The number of transactions committed in this client session.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_commit_count_replica

The number of transactions committed by this replica.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_commit_count_slave

Deprecated synonym for Ndb_api_trans_commit_count_replica.

Ndb_api_trans_commit_count

The number of transactions committed by this MySQL Server (SQL node).

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_local_read_row_count_session

The total number of rows that have been read in this client session. This includes all rows read by any primary key, unique key, or scan operation made in this client session.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_local_read_row_count_replica

The total number of rows that have been read by this replica. This includes all rows read by any primary key, unique key, or scan operation made by this replica.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_local_read_row_count_slave

Deprecated synonym for Ndb_api_trans_local_read_row_count_replica.

Ndb_api_trans_local_read_row_count

The total number of rows that have been read by this MySQL Server (SQL node). This includes all rows read by any primary key, unique key, or scan operation made by this MySQL Server (SQL node).

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_start_count_session

The number of transactions started in this client session.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_start_count_replica

The number of transactions started by this replica.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_trans_start_count_slave

Deprecated synonym for Ndb_api_trans_start_count_replica.

Ndb_api_trans_start_count

The number of transactions started by this MySQL Server (SQL node).

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_uk_op_count_session

The number of operations in this client session based on or using unique keys.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_uk_op_count_replica

The number of operations by this replica based on or using unique keys.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_uk_op_count_slave

Deprecated synonym for Ndb_api_uk_op_count_replica.

Ndb_api_uk_op_count

The number of operations by this MySQL Server (SQL node) based on or using unique keys.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_exec_complete_count_session

The number of times a thread has been blocked in this client session while waiting for execution of an operation to complete. This includes all execute() calls as well as implicit executes for blob and auto-increment operations not visible to clients.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_exec_complete_count_replica

The number of times a thread has been blocked by this replica while waiting for execution of an operation to complete. This includes all execute() calls as well as implicit executes for blob and auto-increment operations not visible to clients.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_exec_complete_count_slave

Deprecated synonym for Ndb_api_wait_exec_complete_count_replica.

Ndb_api_wait_exec_complete_count

The number of times a thread has been blocked by this MySQL Server (SQL node) while waiting for execution of an operation to complete. This includes all execute() calls as well as implicit executes for blob and auto-increment operations not visible to clients.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_meta_request_count_session

The number of times a thread has been blocked in this client session waiting for a metadata-based signal, such as is expected for DDL requests, new epochs, and seizure of transaction records.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_meta_request_count_replica

The number of times a thread has been blocked by this replica waiting for a metadata-based signal, such as is expected for DDL requests, new epochs, and seizure of transaction records.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_meta_request_count_slave

Deprecated synonym for Ndb_api_wait_meta_request_count_replica.

Ndb_api_wait_meta_request_count

The number of times a thread has been blocked by this MySQL Server (SQL node) waiting for a metadata-based signal, such as is expected for DDL requests, new epochs, and seizure of transaction records.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_nanos_count_session

Total time (in nanoseconds) spent in this client session waiting for any type of signal from the data nodes.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_nanos_count_replica

Total time (in nanoseconds) spent by this replica waiting for any type of signal from the data nodes.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_nanos_count_slave

Deprecated synonym for Ndb_api_wait_nanos_count_replica.

Ndb_api_wait_nanos_count

Total time (in nanoseconds) spent by this MySQL Server (SQL node) waiting for any type of signal from the data nodes.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_scan_result_count_session

The number of times a thread has been blocked in this client session while waiting for a scan-based signal, such as when waiting for more results from a scan, or when waiting for a scan to close.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it relates to the current session only, and is not affected by any other clients of this mysqld.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_scan_result_count_replica

The number of times a thread has been blocked by this replica while waiting for a scan-based signal, such as when waiting for more results from a scan, or when waiting for a scan to close.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope. If this MySQL server does not act as a replica, or does not use NDB tables, this value is always 0.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_api_wait_scan_result_count_slave

Deprecated synonym for Ndb_api_wait_scan_result_count_replica.

Ndb_api_wait_scan_result_count

The number of times a thread has been blocked by this MySQL Server (SQL node) while waiting for a scan-based signal, such as when waiting for more results from a scan, or when waiting for a scan to close.

Although this variable can be read using either SHOW GLOBAL STATUS or SHOW SESSION STATUS, it is effectively global in scope.

For more information, see Section 25.6.16, “NDB API Statistics Counters and Variables”.

Ndb_cluster_node_id

If the server is acting as an NDB Cluster node, then the value of this variable its node ID in the cluster.

If the server is not part of an NDB Cluster, then the value of this variable is 0.

Ndb_config_from_host

If the server is part of an NDB Cluster, the value of this variable is the host name or IP address of the Cluster management server from which it gets its configuration data.

If the server is not part of an NDB Cluster, then the value of this variable is an empty string.

Ndb_config_from_port

If the server is part of an NDB Cluster, the value of this variable is the number of the port through which it is connected to the Cluster management server from which it gets its configuration data.

If the server is not part of an NDB Cluster, then the value of this variable is 0.

Ndb_config_generation

Shows the generation number of the cluster's current configuration. This can be used as an indicator to determine whether the configuration of the cluster has changed since this SQL node last connected to the cluster.

Ndb_conflict_fn_epoch

Used in NDB Cluster Replication conflict resolution, this variable shows the number of rows found to be in conflict using NDB$EPOCH() conflict resolution on a given mysqld since the last time it was restarted.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_fn_epoch_trans

Used in NDB Cluster Replication conflict resolution, this variable shows the number of rows found to be in conflict using NDB$EPOCH_TRANS() conflict resolution on a given mysqld since the last time it was restarted.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_fn_epoch2

Shows the number of rows found to be in conflict in NDB Cluster Replication conflict resolution, when using NDB$EPOCH2(), on the source designated as the primary since the last time it was restarted.

For more information, see NDB$EPOCH2().

Ndb_conflict_fn_epoch2_trans

Used in NDB Cluster Replication conflict resolution, this variable shows the number of rows found to be in conflict using NDB$EPOCH_TRANS2() conflict resolution on a given mysqld since the last time it was restarted.

For more information, see NDB$EPOCH2_TRANS().

Ndb_conflict_fn_max

Used in NDB Cluster Replication conflict resolution, this variable shows the number of times that a row was not applied on the current SQL node due to “greatest timestamp wins” conflict resolution since the last time that this mysqld was started.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_fn_max_del_win

Shows the number of times that a row was rejected on the current SQL node due to NDB Cluster Replication conflict resolution using NDB$MAX_DELETE_WIN(), since the last time that this mysqld was started.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_fn_max_del_win_ins

Shows the number of times that insertion of a row was rejected on the current SQL node due to NDB Cluster Replication conflict resolution using NDB$MAX_DEL_WIN_INS(), since the last time that this mysqld was started.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_fn_max_ins

Used in NDB Cluster Replication conflict resolution, this variable shows the number of times that a row was not inserted on the current SQL node due to “greatest timestamp wins” conflict resolution since the last time that this mysqld was started.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_fn_old

Used in NDB Cluster Replication conflict resolution, this variable shows the number of times that a row was not applied as the result of “same timestamp wins” conflict resolution on a given mysqld since the last time it was restarted.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_last_conflict_epoch

The most recent epoch in which a conflict was detected on this replica. You can compare this value with Ndb_replica_max_replicated_epoch; if Ndb_replica_max_replicated_epoch is greater than Ndb_conflict_last_conflict_epoch, no conflicts have yet been detected.

See Section 25.7.12, “NDB Cluster Replication Conflict Resolution”, for more information.

Ndb_conflict_reflected_op_discard_count

When using NDB Cluster Replication conflict resolution, this is the number of reflected operations that were not applied on the secondary, due to encountering an error during execution.

See Section 25.7.12, “NDB Cluster Replication Conflict Resolution”, for more information.

Ndb_conflict_reflected_op_prepare_count

When using conflict resolution with NDB Cluster Replication, this status variable contains the number of reflected operations that have been defined (that is, prepared for execution on the secondary).

See Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_refresh_op_count

When using conflict resolution with NDB Cluster Replication, this gives the number of refresh operations that have been prepared for execution on the secondary.

See Section 25.7.12, “NDB Cluster Replication Conflict Resolution”, for more information.

Ndb_conflict_last_stable_epoch

Number of rows found to be in conflict by a transactional conflict function

See Section 25.7.12, “NDB Cluster Replication Conflict Resolution”, for more information.

Ndb_conflict_trans_row_conflict_count

Used in NDB Cluster Replication conflict resolution, this status variable shows the number of rows found to be directly in-conflict by a transactional conflict function on a given mysqld since the last time it was restarted.

Currently, the only transactional conflict detection function supported by NDB Cluster is NDB$EPOCH_TRANS(), so this status variable is effectively the same as Ndb_conflict_fn_epoch_trans.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_trans_row_reject_count

Used in NDB Cluster Replication conflict resolution, this status variable shows the total number of rows realigned due to being determined as conflicting by a transactional conflict detection function. This includes not only Ndb_conflict_trans_row_conflict_count, but any rows in or dependent on conflicting transactions.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_trans_reject_count

Used in NDB Cluster Replication conflict resolution, this status variable shows the number of transactions found to be in conflict by a transactional conflict detection function.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_trans_detect_iter_count

Used in NDB Cluster Replication conflict resolution, this shows the number of internal iterations required to commit an epoch transaction. Should be (slightly) greater than or equal to Ndb_conflict_trans_conflict_commit_count.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_conflict_trans_conflict_commit_count

Used in NDB Cluster Replication conflict resolution, this shows the number of epoch transactions committed after they required transactional conflict handling.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_epoch_delete_delete_count

When using delete-delete conflict detection, this is the number of delete-delete conflicts detected, where a delete operation is applied, but the indicated row does not exist.

Ndb_execute_count

Provides the number of round trips to the NDB kernel made by operations.

Ndb_last_commit_epoch_server

The epoch most recently committed by NDB.

Ndb_last_commit_epoch_session

The epoch most recently committed by this NDB client.

Ndb_metadata_detected_count

The number of times since this server was last started that the NDB metadata change detection thread has discovered changes with respect to the MySQL data dictionary.

Ndb_metadata_excluded_count

The number of metadata objects that the NDB binlog thread has been unable to synchronize on this SQL node since it was last restarted.

Should an object be excluded, it is not again considered for automatic synchronization until the user corrects the mismatch manually. This can be done by attempting to use the table with a statement such as SHOW CREATE TABLE table, SELECT * FROM table, or any other statement that would trigger table discovery.

Ndb_metadata_synced_count

The number of NDB metadata objects which have been synchronized on this SQL node since it was last restarted.

Ndb_number_of_data_nodes

If the server is part of an NDB Cluster, the value of this variable is the number of data nodes in the cluster.

If the server is not part of an NDB Cluster, then the value of this variable is 0.

Ndb_pushed_queries_defined

The total number of joins pushed down to the NDB kernel for distributed handling on the data nodes.

Ndb_pushed_queries_dropped

The number of joins that were pushed down to the NDB kernel but that could not be handled there.

Ndb_pushed_queries_executed

The number of joins successfully pushed down to NDB and executed there.

Ndb_pushed_reads

The number of rows returned to mysqld from the NDB kernel by joins that were pushed down.

Ndb_pruned_scan_count

This variable holds a count of the number of scans executed by NDBCLUSTER since the NDB Cluster was last started where NDBCLUSTER was able to use partition pruning.

Using this variable together with Ndb_scan_count can be helpful in schema design to maximize the ability of the server to prune scans to a single table partition, thereby involving replica only a single data node.

Ndb_replica_max_replicated_epoch

The most recently committed epoch on this replica. You can compare this value with Ndb_conflict_last_conflict_epoch; if Ndb_replica_max_replicated_epoch is the greater of the two, no conflicts have yet been detected.

For more information, see Section 25.7.12, “NDB Cluster Replication Conflict Resolution”.

Ndb_scan_count

This variable holds a count of the total number of scans executed by NDBCLUSTER since the NDB Cluster was last started.

Ndb_slave_max_replicated_epoch

Deprecated synonym for Ndb_replica_max_replicated_epoch.

Ndb_system_name

If this MySQL Server is connected to an NDB cluster, this read-only variable shows the cluster system name. Otherwise, the value is an empty string.

Ndb_trans_hint_count_session

The number of transactions using hints that have been started in the current session. Compare with Ndb_api_trans_start_count_session to obtain the proportion of all NDB transactions able to use hints.