Index of wsrep system variables¶

Percona XtraDB Cluster introduces a number of MySQL system variables related to write-set replication.

`pxc_encrypt_cluster_traffic`¶

Option	Description
Command Line:	`--pxc-encrypt-cluster-traffic`
Config File:	Yes
Scope:	Global
Dynamic:	No
Default Value:	`ON`

Enables automatic configuration of SSL encryption. When disabled, you need to configure SSL manually to encrypt Percona XtraDB Cluster traffic.

Possible values:

ON, 1, true: Enabled (default)
OFF, 0, false: Disabled

For more information, see SSL Automatic Configuration.

`pxc_maint_mode`¶

Option	Description
Command Line:	`--pxc-maint-mode`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`DISABLED`

Specifies the maintenance mode for taking a node down without adjusting settings in ProxySQL.

The following values are available:

DISABLED: This is the default state that tells ProxySQL to route traffic to the node as usual.
SHUTDOWN: This state is set automatically when you initiate node shutdown.
MAINTENANCE: You can manually change to this state if you need to perform maintenance on a node without shutting it down.

For more information, see Assisted Maintenance Mode.

`pxc_maint_transition_period`¶

Option	Description
Command Line:	`--pxc-maint-transition-period`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`10` (ten seconds)

Defines the transition period when you change pxc_maint_mode to SHUTDOWN or MAINTENANCE. By default, the period is set to 10 seconds, which should be enough for most transactions to finish. You can increase the value to accommodate for longer-running transactions.

For more information, see Assisted Maintenance Mode.

`pxc_strict_mode`¶

Option	Description
Command Line:	`--pxc-strict-mode`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`ENFORCING` or `DISABLED`

Controls PXC Strict Mode, which runs validations to avoid the use of experimental and unsupported features in Percona XtraDB Cluster.

Depending on the actual mode you select, upon encountering a failed validation, the server will either throw an error (halting startup or denying the operation), or log a warning and continue running as normal. The following modes are available:

DISABLED: Do not perform strict mode validations and run as normal.
PERMISSIVE: If a validation fails, log a warning and continue running as normal.
ENFORCING: If a validation fails during startup, halt the server and throw an error. If a validation fails during runtime, deny the operation and throw an error.
MASTER: The same as ENFORCING except that the validation of explicit table locking is not performed. This mode can be used with clusters in which write operations are isolated to a single node.

By default, pxc_strict_mode is set to ENFORCING, except if the node is acting as a standalone server or the node is bootstrapping, then pxc_strict_mode defaults to DISABLED.

Note

When changing the value of pxc_strict_mode from DISABLED or PERMISSIVE to ENFORCING or MASTER, ensure that the following configuration is used:

wsrep_replicate_myisam=OFF
binlog_format=ROW
log_output=FILE or log_output=NONE or log_output=FILE,NONE

The SERIALIZABLE method of isolation is not allowed in ENFORCING mode.

For more information, see PXC Strict Mode.

`wsrep_applier_FK_checks`¶

Option	Description
Command Line:	`--wsrep-applier-FK-checks`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`ON`

As of Percona XtraDB Cluster 8.0.26-16, the wsrep_slave_FK_checks variable is deprecated in favor of this variable.

Defines whether foreign key checking is done for applier threads. This is enabled by default.

`wsrep_applier_threads`¶

Option	Description
Command Line:	`--wsrep-applier-threads`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`1`

As of Percona XtraDB Cluster 8.0.26-16, the wsrep_slave_threads variable is deprecated and may be removed in a later version. Use the wsrep_applier_threads variable.

Specifies the number of threads that can apply replication transactions in parallel. Galera supports true parallel replication that applies transactions in parallel only when it is safe to do so. This variable is dynamic. You can increase/decrease it at any time.

Note

When you decrease the number of threads, it won’t kill the threads immediately, but stop them after they are done applying current transaction (the effect with an increase is immediate though).

If any replication consistency problems are encountered, it’s recommended to set this back to 1 to see if that resolves the issue. The default value can be increased for better throughput.

You may want to increase it as suggested in Codership documentation for flow control: when the node is in JOINED state, increasing the number of replica threads can speed up the catchup to SYNCED.

You can also estimate the optimal value for this from wsrep_cert_deps_distance as suggested in the Galera Cluster documentation.

For more configuration tips, see Setting Parallel Slave Threads`.

`wsrep_applier_UK_checks`¶

Option	Description
Command Line:	`--wsrep-applier-UK-checks`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`OFF`

As of Percona XtraDB Cluster 8.0.26-16, the wsrep_slave_UK_checks variable is deprecated and may be removed in a later version. Use the wsrep_applier_UK_checks variable.

Defines whether unique key checking is done for applier threads. This is disabled by default.

`wsrep_auto_increment_control`¶

Option	Description
Command Line:	`--wsrep-auto-increment-control`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`ON`

Enables automatic adjustment of auto-increment system variables depending on the size of the cluster:

auto_increment_increment controls the interval between successive AUTO_INCREMENT column values
auto_increment_offset determines the starting point for the AUTO_INCREMENT column value

This helps prevent auto-increment replication conflicts across the cluster by giving each node its own range of auto-increment values. It is enabled by default.

Automatic adjustment may not be desirable depending on application’s use and assumptions of auto-increments. It can be disabled in source-replica clusters.

`wsrep_causal_reads`¶

Option	Description
Command Line:	`--wsrep-causal-reads`
Config File:	Yes
Scope:	Global, Session
Dynamic:	Yes
Default Value:	`OFF`

In some cases, the source may apply events faster than a replica, which can cause source and replica to become out of sync for a brief moment. When this variable is set to ON, the replica will wait until that event is applied before doing any other queries. Enabling this variable will result in larger latencies.

Note

This variable was deprecated because enabling it is the equivalent of setting wsrep_sync_wait to 1.

`wsrep_certification_rules`¶

Option	Description
Command Line:	`--wsrep-certification-rules`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Values:	STRICT, OPTIMIZED
Default Value:	STRICT

This variable controls how certification is done in the cluster, in particular this affects how foreign keys are handled.

STRICT Two INSERTs that happen at about the same time on two different nodes in a child table, that insert different (non conflicting rows), but both rows point to the same row in the parent table may result in the certification failure.

OPTIMIZED Two INSERTs that happen at about the same time on two different nodes in a child table, that insert different (non conflicting rows), but both rows point to the same row in the parent table will not result in the certification failure.

`wsrep_certify_nonPK`¶

Option	Description
Command Line:	`--wsrep-certify-nonpk`
Config File:	Yes
Scope:	Global
Dynamic:	No
Default Value:	`ON`

Enables automatic generation of primary keys for rows that don’t have them. Write set replication requires primary keys on all tables to allow for parallel applying of transactions. This variable is enabled by default. As a rule, make sure that all tables have primary keys.

See also

MySQL wsrep option: wsrep_certify_nonPK

`wsrep_cluster_address`¶

Option	Description
Command Line:	`--wsrep-cluster-address`
Config File:	Yes
Scope:	Global
Dynamic:	Yes

Defines the back-end schema, IP addresses, ports, and options that the node uses when connecting to the cluster. This variable needs to specify at least one other node’s address, which is alive and a member of the cluster. In practice, it is best (but not necessary) to provide a complete list of all possible cluster nodes. The value should be of the following format:

<schema>://<address>[?<option1>=<value1>[&<option2>=<value2>]],...

The only back-end schema currently supported is gcomm. The IP address can contain a port number after a colon. Options are specified after ? and separated by &. You can specify multiple addresses separated by commas.

For example:

wsrep_cluster_address="gcomm://192.168.0.1:4567?gmcast.listen_addr=0.0.0.0:5678"

If an empty gcomm:// is provided, the node will bootstrap itself (that is, form a new cluster). It is not recommended to have empty cluster address in production config after the cluster has been bootstrapped initially. If you want to bootstrap a new cluster with a node, you should pass the --wsrep-new-cluster option when starting.

`wsrep_cluster_name`¶

Option	Description
Command Line:	`--wsrep-cluster-name`
Config File:	Yes
Scope:	Global
Dynamic:	No
Default Value:	`my_wsrep_cluster`

Specifies the name of the cluster and must be identical on all nodes. A node checks the value when attempting to connect to the cluster. If the names match, the node connects.

Edit the value in the my.cnf in the [galera] section.

[galera]

    wsrep_cluster_name=simple-cluster

Execute SHOW VARIABLES with the LIKE operator to view the variable:

mysql> SHOW VARIABLES LIKE 'wsrep_cluster_name';

Expected output

+--------------------+----------------+
| Variable_name      | Value          |
+--------------------+----------------+
| wsrep_cluster_name | simple-cluster |
+--------------------+----------------+

Note

It should not exceed 32 characters. A node cannot join the cluster if the cluster names do not match. You must re-bootstrap the cluster after a name change.

See also

MySQL wsrep option: wsrep_cluster_name

`wsrep_data_home_dir`¶

Option	Description
Command Line:	No
Config File:	Yes
Scope:	Global
Dynamic:	No
Default Value:	`/var/lib/mysql` (or whatever path is specified by `datadir`)

Specifies the path to the directory where the wsrep provider stores its files (such as grastate.dat).

See also

MySQL wsrep option: wsrep_data_home_dir

`wsrep_dbug_option`¶

Option	Description
Command Line:	`--wsrep-dbug-option`
Config File:	Yes
Scope:	Global
Dynamic:	Yes

Defines DBUG options to pass to the wsrep provider.

See also

MySQL wsrep option: wsrep_dbug_option

`wsrep_debug`¶

Option	Description
Command Line:	`--wsrep-debug`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`NONE`

Enables debug level logging for the database server and wsrep-lib - an integration library for WSREP API with additional convenience for transaction processing. By default, --wsrep-debug variable is disabled.

This variable can be used when trying to diagnose problems or when submitting a bug.

You can set wsrep_debug in the following my.cnf groups:

Under [mysqld] it enables debug logging for mysqld and the SST script.
Under [sst] it enables debug logging for the SST script only.

This variable may be set to one of the following values:

NONE

No debug-level messages.

SERVER

wsrep-lib general debug-level messages and detailed debug-level messages from the server_state part are printed out. Galera debug-level logs are printed out.

TRANSACTION

Same as SERVER + wsrep-lib transaction part

STREAMING

Same as TRANSACTION + wsrep-lib streaming part

CLIENT

Same as STREAMING + wsrep-lib client_service part

Note

Do not enable debugging in production environments, because it logs authentication info (that is, passwords).

See also

MySQL wsrep option: wsrep_debug

`wsrep_desync`¶

Option	Description
Command Line:	No
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`OFF`

Defines whether the node should participate in Flow Control. By default, this variable is disabled, meaning that if the receive queue becomes too big, the node engages in Flow Control: it works through the receive queue until it reaches a more manageable size. For more information, see wsrep_local_recv_queue and wsrep_flow_control_interval.

Enabling this variable will disable Flow Control for the node. It will continue to receive write-sets that it is not able to apply, the receive queue will keep growing, and the node will keep falling behind the cluster indefinitely.

Toggling this back to OFF will require an IST or an SST, depending on how long it was desynchronized. This is similar to cluster desynchronization, which occurs during RSU TOI. Because of this, it’s not a good idea to enable wsrep_desync for a long period of time or for several nodes at once.

Note

You can also desync a node using the /\*! WSREP_DESYNC \*/ query comment.

See also

MySQL wsrep option: wsrep_desync

`wsrep_dirty_reads`¶

Option	Description
Command Line:	`--wsrep-dirty-reads`
Config File:	Yes
Scope:	Session, Global
Dynamic:	Yes
Default Value:	`OFF`

Defines whether the node accepts read queries when in a non-operational state, that is, when it loses connection to the Primary Component. By default, this variable is disabled and the node rejects all queries, because there is no way to tell if the data is correct.

If you enable this variable, the node will permit read queries (USE, SELECT, LOCK TABLE, and UNLOCK TABLES), but any command that modifies or updates the database on a non-operational node will still be rejected (including DDL and DML statements, such as INSERT, DELETE, and UPDATE).

To avoid deadlock errors, set the wsrep_sync_wait variable to 0 if you enable wsrep_dirty_reads.

You can update the variable with a set_var hint.

mysql> SELECT @@wsrep_dirty_reads;

Expected output

+-----------------------+
| @@wsrep_dirty_reads   |
+=======================+
| OFF                   |
+-----------------------+

mysql> SELECT /*+ SET_VAR(wsrep_dirty_reads=ON) */ @@wsrep_dirty_reads;

Expected output

+-----------------------+
| @@wsrep_dirty_reads   |
+=======================+
| ON                    |
+-----------------------+

See also

MySQL wsrep option: wsrep_dirty_reads

`wsrep_drupal_282555_workaround`¶

Option	Description
Command Line:	`--wsrep-drupal-282555-workaround`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`OFF`

Enables a workaround for MySQL InnoDB bug that affects Drupal (Drupal bug #282555 and MySQL bug #41984). In some cases, duplicate key errors would occur when inserting the DEFAULT value into an AUTO_INCREMENT column.

`wsrep_forced_binlog_format`¶

Option	Description
Command Line:	`--wsrep-forced-binlog-format`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`NONE`

Defines a binary log format that will always be effective, regardless of the client session binlog_format variable value.

Possible values for this variable are:

ROW: Force row-based logging format
STATEMENT: Force statement-based logging format
MIXED: Force mixed logging format
NONE: Do not force the binary log format and use whatever is set by the binlog_format variable (default)

`wsrep_ignore_apply_errors`¶

Option	Description
Command Line:	`--wsrep-ignore-apply-errors`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	0

Defines the rules of wsrep applier behavior on errors. You can change the settings by editing the my.cnf file under [mysqld] or at runtime.

The variable has the following options:

Value	Description
WSREP_IGNORE_ERRORS_NONE	All replication errors are treated as errors and will shutdown the node (default behavior)
WSREP_IGNORE_ERRORS_ON_RECONCILING_DDL	DROP DATABASE, DROP TABLE, DROP INDEX, ALTER TABLE are converted to a warning if they result in ER_DB_DROP_EXISTS, ER_BAD_TABLE_ERROR OR ER_CANT_DROP_FIELD_OR_KEY errors
WSREP_IGNORE_ERRORS_ON_RECONCILING_DML	DELETE events are treated as warnings if they failed because the deleted row was not found (ER_KEY_NOT_FOUND)
WSREP_IGNORE_ERRORS_ON_DDL	All DDL errors will be treated as a warning
WSREP_IGNORE_ERRORS_MAX	Infers WSREP_IGNORE_ERRORS_ON_RECONCILING_DDL, WSREP_IGNORE_ERRORS_ON_RECONCILING_DML and WSREP_IGNORE_ERRORS_ON_DDL

Setting the variable between 0 and 7 has the following behavior:

Setting	Behavior
0	WSREP_IGNORE_ERRORS_NONE
1	WSREP_IGNORE_ERRORS_ON_RECONCILING_DDL
2	WSREP_IGNORE_ERRORS_ON_RECONCILING_DML
3	WSREP_IGNORE_ERRORS_ON_RECONCILING_DDL, WSREP_IGNORE_ERRORS_ON_RECONCILING_DML
4	WSREP_IGNORE_ERRORS_ON_DDL
5	WSREP_IGNORE_ERRORS_ON_DDL, WSREP_IGNORE_ERRORS_ON_RECONCILING_DDL
6	WSREP_IGNORE_ERRORS_ON_DDL, WSREP_IGNORE_ERRORS_ON_RECONCILING_DML
7	WSREP_IGNORE_ERRORS_ON_DDL, WSREP_IGNORE_ERRORS_ON_RECONCILING_DML, WSREP_IGNORE_ERRORS_ON_RECONCILING_DDL

`wsrep_min_log_verbosity`¶

Option	Description
Command Line:	`--wsrep-min-log-verbosity`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	3

This variable defines the minimum logging verbosity of wsrep/Galera and acts in conjunction with the log_error_verbosity variable. The wsrep_min_log_verbosity has the same values as log_error_verbosity.

The actual log verbosity of wsrep/Galera can be greater than the value of wsrep_min_log_verbosity if log_error_verbosity is greater than wsrep_min_log_verbosity.

A few examples:

log_error_verbosity	wsrep_min_log_verbosity	MySQL Logs Verbosity	wsrep Logs Verbosity
2	3	system error, warning	system error, warning, info
1	3	system error	system error, warning, info
1	2	system error	system error, warning
3	1	system error, warning, info	system error, warning, info

Note the case where log_error_verbosity=3 and wsrep_min_log_verbosity=1. The actual log verbosity of wsrep/Galera is 3 (system error, warning, info) because log_error_verbosity is greater.

Galera Cluster Documentation: Database Server Logs

`wsrep_load_data_splitting`¶

Option	Description
Command Line:	`--wsrep-load-data-splitting`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`ON`

Defines whether the node should split large LOAD DATA transactions. This variable is enabled by default, meaning that LOAD DATA commands are split into transactions of 10 000 rows or less.

If you disable this variable, then huge data loads may prevent the node from completely rolling the operation back in the event of a conflict, and whatever gets committed stays committed.

Note

It doesn’t work as expected with autocommit=0 when enabled.

`wsrep_log_conflicts`¶

Option	Description
Command Line:	`--wsrep-log-conflicts`
Config File:	Yes
Scope:	Global
Dynamic:	No
Default Value:	`OFF`

Defines whether the node should log additional information about conflicts. By default, this variable is disabled and Percona XtraDB Cluster uses standard logging features in MySQL.

If you enable this variable, it will also log table and schema where the conflict occurred, as well as the actual values for keys that produced the conflict.

See also

MySQL wsrep option: wsrep_log_conflicts

`wsrep_max_ws_rows`¶

Option	Description
Command Line:	`--wsrep-max-ws-rows`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`0` (no limit)

Defines the maximum number of rows each write-set can contain.

By default, there is no limit for the maximum number of rows in a write-set. The maximum allowed value is 1048576.

See also

MySQL wsrep option: wsrep_max_ws_rows

`wsrep_max_ws_size`¶

Option	Description
Command Line:	`--wsrep_max_ws_size`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`2147483647` (2 GB)

Defines the maximum write-set size (in bytes). Anything bigger than the specified value will be rejected.

You can set it to any value between 1024 and the default 2147483647.

See also

MySQL wsrep option: wsrep_max_ws_size

`wsrep_mode`¶

Option	Description
Command Line:	`--wsrep-mode`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:

Defines the node behavior according to a specified value. The value is empty or disabled by default.

The available values are:

Empty - does not change the node behavior.
IGNORE_NATIVE_REPLICATION_FILTER_RULES - changes the wsrep behavior to ignore native replication filter rules.

See also

MySQL wsrep option: wsrep_mode

`wsrep_node_address`¶

Option	Description
Command Line:	`--wsrep-node-address`
Config File:	Yes
Scope:	Global
Dynamic:	No
Default Value:	IP of the first network interface (`eth0`) and default port (`4567`)

Specifies the network address of the node. By default, this variable is set to the IP address of the first network interface (usually eth0 or enp2s0) and the default port (4567).

While default value should be correct in most cases, there are situations when you need to specify it manually. For example:

Servers with multiple network interfaces
Servers that run multiple nodes
Network Address Translation (NAT)
Clusters with nodes in more than one region
Container deployments, such as Docker
Cloud deployments, such as Amazon EC2 (use the global DNS name instead of the local IP address)

The value should be specified in the following format:

<ip_address>[:port]

Note

The value of this variable is also used as the default value for the wsrep_sst_receive_address variable and the ist.recv_addr option.

See also

MySQL wsrep option: wsrep_node_address

`wsrep_node_incoming_address`¶

Option	Description
Command Line:	`--wsrep-node-incoming-address`
Config File:	Yes
Scope:	Global
Dynamic:	No
Default Value:	`AUTO`

Specifies the network address from which the node expects client connections. By default, it uses the IP address from wsrep_node_address and port number 3306.

This information is used for the wsrep_incoming_addresses variable which shows all active cluster nodes.

`wsrep_node_name`¶

Option	Description
Command Line:	`--wsrep-node-name`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	The node’s host name

Defines a unique name for the node. Defaults to the host name.

In many situations, you may use the value of this variable as a means to identify the given node in the cluster as the alternative to using the node address (the value of the wsrep_node_address).

Note

The variable wsrep_sst_donor is an example where you may only use the value of wsrep_node_name and the node address is not permitted.

`wsrep_notify_cmd`¶

Option	Description
Command Line:	`--wsrep-notify-cmd`
Config File:	Yes
Scope:	Global
Dynamic:	No

Specifies the notification command that the node should execute whenever cluster membership or local node status changes. This can be used for alerting or to reconfigure load balancers.

Note

The node will block and wait until the command or script completes and returns before it can proceed. If the script performs any potentially blocking or long-running operations, such as network communication, you should consider initiating such operations in the background and have the script return immediately.

See also

MySQL wsrep option: wsrep_notify_cmd

`wsrep_on`¶

Option	Description
Command Line:	No
Config File:	No
Scope:	Session
Dynamic:	Yes
Default Value:	`ON`

Defines if current session transaction changes for a node are replicated to the cluster.

If set to OFF for a session, no transaction changes are replicated in that session. The setting does not cause the node to leave the cluster, and the node communicates with other nodes.

See also

MySQL wsrep option: wsrep_on

`wsrep_OSU_method`¶

Option	Description
Command Line:	`--wsrep-OSU-method`
Config File:	Yes
Scope:	Global, Session
Dynamic:	Yes
Default Value:	`TOI`

Defines the method for Online Schema Upgrade that the node uses to replicate DDL statements.

For information on the available methods, see Online Schema upgrade and for information on Non-blocking operations, see NBO.

See also

MySQL wsrep option: wsrep_OSU_method

`wsrep_provider`¶

Option	Description
Command Line:	`--wsrep-provider`
Config File:	Yes
Scope:	Global
Dynamic:	No

Specifies the path to the Galera library. This is usually /usr/lib64/libgalera_smm.so on CentOS/RHEL and /usr/lib/libgalera_smm.so on Debian/Ubuntu.

If you do not specify a path or the value is not valid, the node will behave as standalone instance of MySQL.

See also

MySQL wsrep option: wsrep_provider

`wsrep_provider_options`¶

Option	Description
Command Line:	`--wsrep-provider-options`
Config File:	Yes
Scope:	Global
Dynamic:	No

Specifies optional settings for the replication provider documented in Index of :variable:`wsrep_provider` options. These options affect how various situations are handled during replication.

`wsrep_recover`¶

Option	Description
Command Line:	`--wsrep-recover`
Config File:	Yes
Scope:	Global
Dynamic:	No
Default Value:	`OFF`
Location:	mysqld_safe`

Recovers database state after crash by parsing GTID from the log. If the GTID is found, it will be assigned as the initial position for server.

`wsrep_reject_queries`¶

Option	Description
Command Line:	No
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`NONE`

Defines whether the node should reject queries from clients. Rejecting queries can be useful during upgrades, when you want to keep the node up and apply write-sets without accepting queries.

When a query is rejected, the following error is returned:

Error 1047: Unknown command

The following values are available:

NONE: Accept all queries from clients (default)
ALL: Reject all new queries from clients, but maintain existing client connections
ALL_KILL: Reject all new queries from clients and kill existing client connections

Note

This variable doesn’t affect Galera replication in any way, only the applications that connect to the database are affected. If you want to desync a node, use wsrep_desync.

`wsrep_replicate_myisam`¶

Option	Description
Command Line:	`--wsrep-replicate-myisam`
Config File:	Yes
Scope:	Session, Global
Dynamic:	No
Default Value:	`OFF`

Defines whether DML statements for MyISAM tables should be replicated. It is disabled by default, because MyISAM replication is still experimental.

On the global level, wsrep_replicate_myisam can be set only during startup. On session level, you can change it during runtime as well.

For older nodes in the cluster, wsrep_replicate_myisam should work since the TOI decision (for MyISAM DDL) is done on origin node. Mixing of non-MyISAM and MyISAM tables in the same DDL statement is not recommended when wsrep_replicate_myisam is disabled, since if any table in the list is MyISAM, the whole DDL statement is not put under TOI.

Note

You should keep in mind the following when using MyISAM replication:

DDL (CREATE/DROP/TRUNCATE) statements on MyISAM will be replicated irrespective of wsrep_replicate_myisam value
DML (INSERT/UPDATE/DELETE) statements on MyISAM will be replicated only ifwsrep_replicate_myisam is enabled
SST will get full transfer irrespective of wsrep_replicate_myisamvalue (it will get MyISAM tables from donor)
Difference in configuration of pxc-cluster node on enforce_storage_engine front may result in picking up different engine for the same table on different nodes
CREATE TABLE AS SELECT (CTAS) statements use TOI replication. MyISAM tables are created and loaded even if wsrep_replicate_myisam is set to ON.

`wsrep_restart_replica`¶

Option	Description
Command Line:	`--wsrep-restart-replica`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`OFF`

As of Percona XtraDB Cluster 8.0.26-16, the wsrep_restart_slave variable is deprecated in favor of this variable.

Defines whether replication replica should be restarted when the node joins back to the cluster. Enabling this can be useful because asynchronous replication replica thread is stopped when the node tries to apply the next replication event while the node is in non-primary state.

See also

MySQL wsrep option: wsrep_restart_slave

`wsrep_restart_slave`¶

Option	Description
Command Line:	`--wsrep-restart-slave`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`OFF`

As of Percona XtraDB Cluster 8.0.26-16, the wsrep_restart_slave variable is deprecated and may be removed in later versions. Use wsrep_restart_replica.

Defines whether replication replica should be restarted when the node joins back to the cluster. Enabling this can be useful because asynchronous replication replica thread is stopped when the node tries to apply the next replication event while the node is in non-primary state.

`wsrep_retry_autocommit`¶

Option	Description
Command Line:	`--wsrep-retry-autocommit`
Config File:	Yes
Scope:	Global
Dynamic:	No
Default Value:	`1`

Specifies the number of times autocommit transactions will be retried in the cluster if it encounters certification errors. In case there is a conflict, it should be safe for the cluster node to simply retry the statement without returning an error to the client, hoping that it will pass next time.

This can be useful to help an application using autocommit to avoid deadlock errors that can be triggered by replication conflicts.

If this variable is set to 0, autocommit transactions won’t be retried.

`wsrep_RSU_commit_timeout`¶

Option	Description
Command Line:	`--wsrep-RSU-commit-timeout`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`5000`
Range:	From `5000` (5 milliseconds) to `31536000000000` (365 days)

Specifies the timeout in microseconds to allow active connection to complete COMMIT action before starting RSU.

While running RSU it is expected that user has isolated the node and there is no active traffic executing on the node. RSU has a check to ensure this, and waits for any active connection in COMMIT state before starting RSU.

By default this check has timeout of 5 milliseconds, but in some cases COMMIT is taking longer. This variable sets the timeout, and has allowed values from the range of (5 milliseconds, 365 days). The value is to be set in microseconds. Unit of variable is in micro-secs so set accordingly.

Note

RSU operation will not auto-stop node from receiving active traffic. So there could be a continuous flow of active traffic while RSU continues to wait, and that can result in RSU starvation. User is expected to block active RSU traffic while performing operation.

`wsrep_slave_FK_checks`¶

Option	Description
Command Line:	`--wsrep-slave-FK-checks`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`ON`

As of Percona XtraDB Cluster 8.0.26-16, this variable is deprecated and may be removed in a later version. Use the wsrep_applier_FK_checks variable.

Defines whether foreign key checking is done for applier threads. This is enabled by default.

`wsrep_slave_threads`¶

Option	Description
Command Line:	`--wsrep-slave-threads`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`1`

As of Percona XtraDB Cluster 8.0.26-16, this variable is deprecated and may be removed in a later version. Use the wsrep_applier_threads variable.

Specifies the number of threads that can apply replication transactions in parallel. Galera supports true parallel replication that applies transactions in parallel only when it is safe to do so. This variable is dynamic. You can increase/decrease it at any time.

Note

When you decrease the number of threads, it won’t kill the threads immediately, but stop them after they are done applying current transaction (the effect with an increase is immediate though).

If any replication consistency problems are encountered, it’s recommended to set this back to 1 to see if that resolves the issue. The default value can be increased for better throughput.

You may want to increase it as suggested in Codership documentation for flow control: when the node is in JOINED state, increasing the number of replica threads can speed up the catchup to SYNCED.

You can also estimate the optimal value for this from wsrep_cert_deps_distance as suggested in the Galera Cluster documentation.

For more configuration tips, see this document.

`wsrep_slave_UK_checks`¶

Option	Description
Command Line:	`--wsrep-slave-UK-checks`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`OFF`

As of Percona XtraDB Cluster 8.0.26-16, this variable is deprecated and may be removed in a later version. Use the wsrep_applier_UK_checks variable.

Defines whether unique key checking is done for applier threads. This is disabled by default.

`wsrep_SR_store`¶

Option	Description
Command Line:	`--wsrep-sr-store`
Config File:	Yes
Scope:	Global
Dynamic:	No
Default Value:	`table`

Defines storage for streaming replication fragments. The available values are table, the default value, and none, which disables the variable.

`wsrep_sst_allowed_methods`¶

Option	Description
Command Line:	`--wsrep_sst_allowed_methods`
Config File:	Yes
Scope:	Global
Dynamic:	No
Default Value:	xtrabackup-v2`, `clone

Percona XtraDB Cluster 8.4.4-1 adds clone to the default value. For older versions of Percona XtraDB Cluster, the default value is xtrabackup-v2.

This variable limits SST methods accepted by the server for wsrep_sst_method variable. The default value is xtrabackup-v2.

`wsrep_sst_donor`¶

Option	Description
Command Line:	Yes
Config File:	Yes
Scope:	Global
Dynamic:	Yes

Specifies a list of nodes (using their wsrep_node_name values) that the current node should prefer as donors for SST and IST.

Warning

Using IP addresses of nodes instead of node names (the value of wsrep_node_name) as values of wsrep_sst_donor results in an error.

ERROR] WSREP: State transfer request failed unrecoverably: 113 (No route
to host). Most likely it is due to inability to communicate with the
cluster primary component. Restart required.

If the value is empty, the first node in SYNCED state in the index becomes the donor and will not be able to serve requests during the state transfer.

To consider other nodes if the listed nodes are not available, add a comma at the end of the list, for example:

wsrep_sst_donor=node1,node2,

If you remove the trailing comma from the previous example, then the joining node will consider only node1 and node2.

Note

By default, the joiner node does not wait for more than 100 seconds to receive the first packet from a donor. This is implemented via the sst-initial-timeout option. If you set the list of preferred donors without the trailing comma or believe that all nodes in the cluster can often be unavailable for SST (this is common for small clusters), then you may want to increase the initial timeout (or disable it completely if you don’t mind the joiner node waiting for the state transfer indefinitely).

See also

MySQL wsrep option: wsrep_sst_donor

`wsrep_sst_method`¶

Option	Description
Command Line:	`--wsrep-sst-method`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	xtrabackup-v2

Defines the method or script for State Snapshot Transfer (SST).

Available values are:

xtrabackup-v2: Uses Percona XtraBackup to perform SST. This value is the default. Privileges and permissions for running Percona XtraBackup can be found in Percona XtraBackup documentation. For more information, see Percona XtraBackup SST Configuration. The xtrabackup-v2 method supports clusters with GTIDs and async replicas.
clone: Introduced in Percona XtraDB Cluster 8.4.4-4, uses the clone method for SST.
skip: Use this to skip SST. Removed in Percona XtraDB Cluster 8.0.33-25. This value can be used when initially starting the cluster and manually restoring the same data to all nodes. This value should not be used permanently because it could lead to data inconsistency across the nodes.
ist_only : Introduced in Percona XtraDB Cluster 8.0.33-25. This value allows only Incremental State Transfer (IST). If a node cannot sync with the cluster with IST, abort that node’s start. This action leaves the data directory unchanged. This value prevents starting a node, after a manual backup restoration, that does not have a grastate.dat file. This missing file could initiate a full-state transfer (SST) which can be a more time and resource-intensive operation.

Note

xtrabackup-v2 provides support for clusters with GTIDs and async replicas.

See also

MySQL wsrep option: wsrep_sst_method

`wsrep_sst_receive_address`¶

Option	Description
Command Line:	`--wsrep-sst-receive-address`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`AUTO`

Specifies the network address where donor node should send state transfers. By default, this variable is set to AUTO, meaning that the IP address from wsrep_node_address is used.

`wsrep_start_position`¶

Option	Description
Command Line:	`--wsrep-start-position`
Config File:	Yes
Scope:	Global
Dynamic:	Yes
Default Value:	`00000000-0000-0000-0000-00000000000000:-1`

Specifies the node’s start position as UUID:seqno. By setting all the nodes to have the same value for this variable, the cluster can be set up without the state transfer.

`wsrep_sync_wait`¶

Option	Description
Command Line:	`--wsrep-sync-wait`
Config File:	Yes
Scope:	Session, Global
Dynamic:	Yes
Default Value:	`0`

Controls cluster-wide causality checks on certain statements. Checks ensure that the statement is executed on a node that is fully synced with the cluster.

You can update the variable with a set_var hint.

   mysql> SELECT @@wsrep_sync_wait;

Expected output

+---------------------+
| @@wsrep_sync_wait   |
+=====================+
| 3                   |
+---------------------+

   mysql> SELECT /*+ SET_VAR(wsrep_sync_wait=7) */ @@wsrep_sync_wait;

Expected output

+---------------------+
| @@wsrep_sync_wait   |
+=====================+
| 7                   |
+---------------------+

Note

Causality checks of any type can result in increased latency.

The type of statements to undergo checks is determined by bitmask:

0: Do not run causality checks for any statements. This is the default.
1: Perform checks for READ statements (including SELECT, SHOW, and BEGIN or START TRANSACTION).
2: Perform checks for UPDATE and DELETE statements.
3: Perform checks for READ, UPDATE, and DELETE statements.
4: Perform checks for INSERT and REPLACE statements.
5: Perform checks for READ, INSERT, and REPLACE statements.
6: Perform checks for UPDATE, DELETE, INSERT, and REPLACE statements.
7: Perform checks for READ, UPDATE, DELETE, INSERT, and REPLACE statements.

Note

Setting wsrep_sync_wait to 1 is the equivalent of setting the deprecated wsrep_causal_reads to ON.

See also

MySQL wsrep option: wsrep_sync_wait

`wsrep_trx_fragment_size`¶

Option	Description
Command Line:	`--wsrep-trx-fragment-size`
Config File:	Yes
Scope:	Global, Session
Dynamic:	Yes
Default Value:	0

Defines the the streaming replication fragment size. This variable is measured in the value defined by wsrep_trx_fragment_unit. The minimum value is 0 and the maximum value is 2147483647.

You can update the variable with a set_var hint.

mysql> SELECT @@@wsrep_trx_fragment_unit; SELECT @@wsrep_trx_fragment_size;

Expected output

+------------------------------+
| @@wsrep_trx_fragment_unit    |
+==============================+
| statements                   |
+------------------------------+
| @@wsrep_trx_fragment_size    |
+------------------------------+
| 3                            |
+------------------------------+

mysql> SELECT /*+ SET_VAR(wsrep_trx_fragment_size=5) */ @@wsrep_trx_fragment_size;

Expected output

+------------------------------+
| @@wsrep_trx_fragment_size    |
+==============================+
| 5                            |
+------------------------------+

You can also use set_var() in a data manipulation language (DML) statement. This ability is useful when streaming large statements within a transaction.

node1> BEGIN;
Query OK, 0 rows affected (0.00 sec)

node1> INSERT /*+SET_VAR(wsrep_trx_fragment_size = 100)*/ INTO t1 SELECT * FROM t1; 
Query OK, 65536 rows affected (15.15 sec)
Records: 65536 Duplicates: 0 Warnings: 0

node1> UPDATE /*+SET_VAR(wsrep_trx_fragment_size = 100)*/ t1 SET i=2;
Query OK, 131072 rows affected (1 min 35.93 sec)
Rows matched: 131072 Changed: 131072 Warnings: 0

node2> SET SESSION TRANSACTION_ISOLATION = 'READ-UNCOMMITTED';
Query OK, 0 rows affected (0.00 sec)

node2> SELECT * FROM t1 LIMIT 5;
+---+
| i |
+===+
| 2 |
+---+
| 2 |
+---+
| 2 |
+---+
| 2 |
+---+
| 2 |
+---+
node1> DELETE  /*+SET_VAR(wsrep_trx_fragment_size = 10000)*/ FROM t1;
Query OK, 131072 rows affected (15.09 sec)

`wsrep_trx_fragment_unit`¶

Option	Description
Command Line:	`--wsrep-trx-fragment-unit`
Config File:	Yes
Scope:	Global, Session
Dynamic:	Yes
Default Value:	“bytes”

Defines the type of measure for the wsrep_trx_fragment_size. The possible values are: bytes, rows, statements.

You can update the variable with a set_var hint.

mysql> SELECT @@wsrep_trx_fragment_unit; SELECT @@wsrep_trx_fragment_size;

Expected output

+------------------------------+
| @@wsrep_trx_fragment_unit    |
+==============================+
| statements                   |
+------------------------------+
| @@wsrep_trx_fragment_size    |
+------------------------------+
| 3                            |
+------------------------------+

mysql> SELECT /*+ SET_VAR(wsrep_trx_fragment_unit=rows) */ @@wsrep_trx_fragment_unit;

Expected output

+------------------------------+
| @@wsrep_trx_fragment_unit    |
+==============================+
| rows                         |
+------------------------------+

Index of wsrep system variables¶

pxc_encrypt_cluster_traffic¶

pxc_maint_mode¶

pxc_maint_transition_period¶

pxc_strict_mode¶

wsrep_applier_FK_checks¶

wsrep_applier_threads¶

wsrep_applier_UK_checks¶

wsrep_auto_increment_control¶

wsrep_causal_reads¶

wsrep_certification_rules¶

wsrep_certify_nonPK¶

wsrep_cluster_address¶

wsrep_cluster_name¶

wsrep_data_home_dir¶

wsrep_dbug_option¶

wsrep_debug¶

wsrep_desync¶

wsrep_dirty_reads¶

wsrep_drupal_282555_workaround¶

wsrep_forced_binlog_format¶

wsrep_ignore_apply_errors¶

wsrep_min_log_verbosity¶

wsrep_load_data_splitting¶

wsrep_log_conflicts¶

wsrep_max_ws_rows¶

wsrep_max_ws_size¶

wsrep_mode¶

wsrep_node_address¶

wsrep_node_incoming_address¶

wsrep_node_name¶

wsrep_notify_cmd¶

wsrep_on¶

wsrep_OSU_method¶

wsrep_provider¶

wsrep_provider_options¶

wsrep_recover¶

wsrep_reject_queries¶

wsrep_replicate_myisam¶

wsrep_restart_replica¶

wsrep_restart_slave¶

wsrep_retry_autocommit¶

wsrep_RSU_commit_timeout¶

wsrep_slave_FK_checks¶

wsrep_slave_threads¶

wsrep_slave_UK_checks¶

wsrep_SR_store¶

wsrep_sst_allowed_methods¶

wsrep_sst_donor¶

wsrep_sst_method¶

wsrep_sst_receive_address¶

wsrep_start_position¶

wsrep_sync_wait¶

wsrep_trx_fragment_size¶

wsrep_trx_fragment_unit¶

`pxc_encrypt_cluster_traffic`¶

`pxc_maint_mode`¶

`pxc_maint_transition_period`¶

`pxc_strict_mode`¶

`wsrep_applier_FK_checks`¶

`wsrep_applier_threads`¶

`wsrep_applier_UK_checks`¶

`wsrep_auto_increment_control`¶

`wsrep_causal_reads`¶

`wsrep_certification_rules`¶

`wsrep_certify_nonPK`¶

`wsrep_cluster_address`¶

`wsrep_cluster_name`¶

`wsrep_data_home_dir`¶

`wsrep_dbug_option`¶

`wsrep_debug`¶

`wsrep_desync`¶

`wsrep_dirty_reads`¶

`wsrep_drupal_282555_workaround`¶

`wsrep_forced_binlog_format`¶

`wsrep_ignore_apply_errors`¶

`wsrep_min_log_verbosity`¶

`wsrep_load_data_splitting`¶

`wsrep_log_conflicts`¶

`wsrep_max_ws_rows`¶

`wsrep_max_ws_size`¶

`wsrep_mode`¶

`wsrep_node_address`¶

`wsrep_node_incoming_address`¶

`wsrep_node_name`¶

`wsrep_notify_cmd`¶

`wsrep_on`¶

`wsrep_OSU_method`¶

`wsrep_provider`¶

`wsrep_provider_options`¶

`wsrep_recover`¶

`wsrep_reject_queries`¶

`wsrep_replicate_myisam`¶

`wsrep_restart_replica`¶

`wsrep_restart_slave`¶

`wsrep_retry_autocommit`¶

`wsrep_RSU_commit_timeout`¶

`wsrep_slave_FK_checks`¶

`wsrep_slave_threads`¶

`wsrep_slave_UK_checks`¶

`wsrep_SR_store`¶

`wsrep_sst_allowed_methods`¶

`wsrep_sst_donor`¶

`wsrep_sst_method`¶

`wsrep_sst_receive_address`¶

`wsrep_start_position`¶

`wsrep_sync_wait`¶

`wsrep_trx_fragment_size`¶

`wsrep_trx_fragment_unit`¶