Index of wsrep system variables

variable wsrep_OSU_method
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:TOI
This variable can be used to select schema upgrade method. Available values are:
  • TOI - Total Order Isolation - When this method is selected DDL is processed in the same order with regards to other transactions in each cluster node. This guarantees data consistency. In case of DDL statements cluster will have parts of database locked and it will behave like a single server. In some cases (like big ALTER TABLE) this could have impact on cluster’s performance and high availability, but it could be fine for quick changes that happen almost instantly (like fast index changes). When DDL is processed under total order isolation (TOI) the DDL statement will be replicated up front to the cluster. i.e. cluster will assign global transaction ID for the DDL statement before the DDL processing begins. Then every node in the cluster has the responsibility to execute the DDL in the given slot in the sequence of incoming transactions, and this DDL execution has to happen with high priority.
  • RSU - Rolling Schema Upgrade - When this method is selected DDL statements won’t be replicated across the cluster, instead it’s up to the user to run them on each node separately. The node applying the changes will desynchronize from the cluster briefly, while normal work happens on all the other nodes. When the DDL statement is processed node will apply delayed replication events. The schema changes must be backwards compatible for this method to work, otherwise the node that receives the change will likely break Galera replication. If the replication breaks the SST will be triggered when the node tries to join again but the change will be undone.
variable wsrep_auto_increment_control
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:ON

This variable manages the auto_increment_increment and auto_increment_offset variables automatically depending on the size of the cluster. This helps prevent auto_increment replication conflicts across the cluster by giving each node it’s own range of auto_increment values. This may not be desirable depending on application’s use and assumptions of auto-increments. It can be turned off in Master/Slave clusters.

variable wsrep_causal_reads
Command Line:Yes
Config File:Yes
Scope:Global, Local
Dynamic:Yes
Default Value:OFF

In some cases master may apply event faster than a slave, which can cause master and slave being out-of-sync for a brief moment. When this variable is set to ON slave will wait till that event is applied before doing any other queries. Enabling this variable will also result in larger latencies.

variable wsrep_certify_nonPK
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:ON

When this variable is enabled, primary keys will be generated automatically for the rows that the rows don’t have them. Using tables without primary keys is not recommended.

variable wsrep_cluster_address
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:No

This minimally needs to be any single other cluster node’s address that 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.  This takes the form of:

gcomm://<node:ip>,<node:ip>,<node:ip>

If an empty gcomm:// is provided, this tells the node to bootstrap it self (i.e., form a new cluster). This is not recommended for production after the cluster has been bootstrapped initially.

variable wsrep_cluster_name
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:my_wsrep_cluster

This is the name of the cluster and should be identical on all nodes belonging to the same cluster.

variable wsrep_convert_LOCK_to_trx
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:OFF

This variable is used to convert LOCK/UNLOCK TABLES statements to BEGIN/COMMIT. Although this can help some older applications to work with multi-master setup it can also result in having huge writesets.

variable wsrep_data_home_dir
Command Line:No
Config File:Yes
Scope:Global
Dynamic:No
Default Value:mysql datadir

This variable can be used to set up the directory where wsrep provider will store its files (like grastate.dat).

variable wsrep_dbug_option
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes

This variable is used to send the DBUG option to the wsrep provider.

variable wsrep_debug
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:OFF

When this variable is set to ON, debug messages will also be logged to the error_log. This can be used when trying to diagnose the problem or when submitting a bug.

variable wsrep_desync
Command Line:No
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:OFF

When this variable is set to ON, the node is desynced from the cluster. Toggling this back will require a IST or a SST depending on how long it was desynced. This is similar to desync which occurs during RSU TOI. This can also be done with /*! WSREP_DESYNC */ query comment.

variable wsrep_drupal_282555_workaround
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:OFF

This variable was introduced as workaround for Drupal/MySQL bug #282555. In some cases duplicate key error would occur when inserting the default value in into the auto_increment field.

variable wsrep_forced_binlog_format
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:NONE
This variable defines a binlog format that will be always be effective regardless of session binlog format setting. Supported options for this variable are:
  • ROW
  • STATEMENT
  • MIXED
  • NONE - This option resets the forced state of the binlog format
variable wsrep_log_conflicts
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:OFF

This variable is used to control whether sole cluster conflicts should be logged. When enabled details of conflicting InnoDB lock will be logged.

variable wsrep_max_ws_rows
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:131072 (128K)

This variable is used to control maximum number of rows each writeset can contain. Anything bigger than this will be rejected.

variable wsrep_max_ws_size
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:1073741824 (1G)

This variable is used to control maximum writeset size (in bytes). Anything bigger than this will be rejected.

variable wsrep_mysql_replication_bundle
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:No
Default Value:0 (no grouping)
Range:0-1000

This variable controls how many replication events will be grouped together. Replication events are grouped in SQL slave thread by skipping events which may cause commit. This way the wsrep node acting in MySQL slave role and all other wsrep nodes in provider replication group, will see same (huge) transactions. This implementation is still experimental. This may help with the bottleneck of having only one MySQL slave facing commit time delay of synchronous provider.

variable wsrep_node_address
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:No
Format :<ip address>[:port]
Default Value:Usually set up as primary network interface (eth0)

This variable is used to specify the network address of the node. In some cases when there are multiple NICs available, state transfer might not work if the default NIC is on different network. Setting this variable explicitly to the correct value will makes SST and IST work correctly out of the box. Even in the multi-network setups, IST/SST can be configured to use other interfaces/addresses.

variable wsrep_node_incoming_address
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:No
Default Value:<wsrep_node_address>:3306

This is the address at which the node accepts client connections. This is information is used for status variable wsrep_incoming_addresses which shows all the active cluster nodes.

variable wsrep_node_name
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes

This variable is used to set up the unique node name.

variable wsrep_notify_cmd
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes

This variable is used to set the notification command that server will execute every time cluster membership or local node status changes.

variable wsrep_on
Command Line:No
Config File:No
Scope:Local, Global
Dynamic:Yes
Default Value:ON

This variable is used to enable/disable wsrep replication. When set to OFF server will stop replication and behave like standalone MySQL server.

variable wsrep_provider
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:None

This variable should contain the path to the Galera library (like /usr/lib64/libgalera_smm.so).

variable wsrep_provider_options
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:No

This variable contains settings currently used by Galera library.

variable wsrep_recover
Command Line:Yes
Config File:No
Scope:Global
Dynamic:No
Default Value:OFF

When server is started with this variable (as --wsrep-recover) it will parse Global Transaction ID from log, and if the GTID is found, output to stderr (which usually goes into the log). This option is used to recover GTID, mysqld is called with this automatically in mysqld_safe, hence running this manually is not required, also no need to set it in my.cnf.

variable wsrep_reject_queries
Command Line:No
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:NONE

This variable can be used to reject queries for that node. This can be useful if someone wants to manually run maintenance on the node like mysqldump without need to change the settings on the load balancer. Following values are supported:

  • NONE - default - nothing is rejected.
  • ALL - all queries are rejected with ‘Error 1047: Unknown command’.
  • ALL_KILL - all queries are rejected and existing client connections are also killed without waiting.

Note, that this doesn’t affect galera replication in any way, only the applications which connect to database are affected. If you are looking for desyncing a node then wsrep_desync is the right option for that.

variable wsrep_replicate_myisam
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:No
Default Value:Off

This variable controls if MyISAM will be replicated or not. MyISAM replication is still experimental and that is one of the reasons why this variable is set to OFF by default.

variable wsrep_retry_autocommit
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:No
Default Value:1

This variable sets the number of times autocommitted transactions will be tried 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 the client’s knowledge with the hopes that it will pass the next time. This can be useful to help an application using autocommit to avoid the deadlock errors that can be triggered by replication conflicts. If this variable is set to 0 transaction won’t be retried and if it is set to 1 it will be retried once.

variable wsrep_slave_threads
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:1

This variable controls the number of threads that can apply replication transactions in parallel. Galera supports true parallel replication, replication that applies transactions in parallel only when it is safe to do so. The variable is dynamic, you can increase/decrease it anytime, note that, when you decrease it, it won’t kill the threads immediately but stop them after they are done applying current transaction (the effect with 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 many a time as suggested here, in JOINED state for instance to speed up the catchup process to SYNCED. You can also estimate the optimal value for this from wsrep_cert_deps_distance as suggested here. You can also refer to this for more configuration tips.

variable wsrep_sst_auth
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Format :<username>:<password>

This variable should contain the authentication information needed for State Snapshot Transfer. Required information depends on the method selected in the wsrep_sst_method. More information about required authentication can be found in the State Snapshot Transfer documentation. This variable will appear masked in the logs and in the SHOW VARIABLES query.

variable wsrep_sst_donor
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes

This variable contains the name (wsrep_node_name) of the preferred donor for the SST. If no node is selected as a preferred donor it will be chosen from one of the available nodes automatically.

variable wsrep_sst_donor_rejects_queries
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:OFF

When this variable is enabled SST donor node will not accept incoming queries, instead it will reject queries with UNKNOWN COMMAND error code. This can be used to signal load-balancer that the node isn’t available.

variable wsrep_sst_method
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:rsync
Recommended :xtrabackup-v2
This variable sets up the method for taking the State Snapshot Transfer (SST). Available options are:
  • xtrabackup - uses Percona XtraBackup to perform the SST, this method requires wsrep_sst_auth to be set up with <user>:<password> which XtraBackup will use on donor. Privileges and permissions needed for running XtraBackup can be found here.
  • xtrabackup-v2 - This is same as xtrabackup SST except that it uses newer protocol, hence is not compatible. This is the recommended option for PXC 5.5.34 and above. For more details, please check Xtrabackup SST Configuration and Percona XtraDB Cluster Errata (as of 5.5.34).
  • rsync - uses rsync to perform the SST, this method doesn’t use the wsrep_sst_auth
  • mysqldump - uses mysqldump to perform the SST, this method requires wsrep_sst_auth to be set up with <user>:<password>, where user has root privileges on the server.
  • custom_script_name - Galera supports Scriptable State Snapshot Transfer. This enables users to create their own custom script for performing an SST.
  • skip - this option can be used to skip the SST, it can be used when initially starting the cluster and manually restore the same data to all nodes. It shouldn’t be used as permanent setting because it could lead to data inconsistency across the nodes.

Note

Note the following:
  • mysqldump SST is not recommended unless it is required for specific reasons. Also, it is not compatible with bind_address = 127.0.0.1 or localhost and will cause startup to fail if set so.
  • Xtrabackup-v2 SST is currently recommended if you have innodb-log-group_home-dir/innodb-data-home-dir in your cnf. Refer to sst-special-dirs for more.
variable wsrep_sst_receive_address
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes
Default Value:AUTO

This variable is used to configure address on which the node expects the SST.

variable wsrep_start_position
Command Line:Yes
Config File:Yes
Scope:Global
Dynamic:Yes

This variable contains the UUID:seqno value. By setting all the nodes to have the same value for this option cluster can be set up without the state transfer.

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