group_replication_exit_state_action

group_replication_flow_control_applier_threshold

group_replication_flow_control_certifier_threshold

group_replication_flow_control_hold_percent

group_replication_flow_control_max_quota

group_replication_flow_control_member_quota_percent

group_replication_flow_control_min_quota

group_replication_flow_control_min_recovery_quota

group_replication_flow_control_mode

group_replication_force_members

group_replication_member_weight

group_replication_transaction_size_limit

group_replication_unreachable_majority_timeout

group_replication_auto_increment_increment

group_replication_compression_threshold

group_replication_transaction_size_limit

group_replication_single_primary_mode

group_replication_enforce_update_everywhere_checks

group_replication_gtid_assignment_block_size

default_table_encryption

lower_case_table_names

transaction_write_set_extraction

group_replication_allow_local_disjoint_gtids_join

Deprecated in version 5.7.21 and scheduled for removal in a future version. Allows the server to join the group even if it has local transactions that are not present in the group.

group_replication_allow_local_lower_version_join

Allows the current server to join the group even if it has a lower major version than the group. With the default setting OFF, servers are not permitted to join a replication group if they have a lower major version than the existing group members. For example, a MySQL 5.7 server cannot join a group that consists of MySQL 8.0 servers. This standard policy ensures that all members of a group are able to exchange messages and apply transactions. Set group_replication_allow_local_lower_version_join to ON only in the following scenarios:

group_replication_auto_increment_increment

Determines the interval between successive column values for transactions that execute on this server instance. This system variable should have the same value on all group members. When Group Replication is started on a server, the value of the server system variable auto_increment_increment is changed to this value, and the value of the server system variable auto_increment_offset is changed to the server ID. These settings avoid the selection of duplicate auto-increment values for writes on group members, which causes rollback of transactions. The changes are reverted when Group Replication is stopped. These changes are only made and reverted if auto_increment_increment and auto_increment_offset each have their default value of 1. If their values have already been modified from the default, Group Replication does not alter them.

The default value of 7 represents a balance between the number of usable values and the permitted maximum size of a replication group (9 members). If your group has more or fewer members, you can set this system variable to match the expected number of group members before Group Replication is started. You cannot change the setting while Group Replication is running.

group_replication_bootstrap_group

Configure this server to bootstrap the group. This option must only be set on one server and only when starting the group for the first time or restarting the entire group. After the group has been bootstrapped, set this option to OFF. It should be set to OFF both dynamically and in the configuration files. Starting two servers or restarting one server with this option set while the group is running may lead to an artificial split brain situation, where two independent groups with the same name are bootstrapped.

group_replication_components_stop_timeout

Timeout, in seconds, that Group Replication waits for each of the components when shutting down.

group_replication_compression_threshold

The threshold value in bytes above which compression is applied to messages sent between group members. If this system variable is set to zero, compression is disabled. The value of group_replication_compression_threshold should be the same on all group members.

Group Replication uses the LZ4 compression algorithm to compress messages sent in the group. Note that the maximum supported input size for the LZ4 compression algorithm is 2113929216 bytes. This limit is lower than the maximum possible value for the group_replication_compression_threshold system variable, which is matched to the maximum message size accepted by XCom. With the LZ4 compression algorithm, do not set a value greater than 2113929216 bytes for group_replication_compression_threshold, because transactions above this size cannot be committed when message compression is enabled.

For more information, see Section 17.9.7.2, “Message Compression”.

group_replication_enforce_update_everywhere_checks

Enable or disable strict consistency checks for multi-primary update everywhere. The default is that checks are disabled. In single-primary mode, this option must be disabled on all group members. In multi-primary mode, when this option is enabled, statements are checked as follows to ensure they are compatible with multi-primary mode:

This system variable is a group-wide configuration setting. It must have the same value on all group members, cannot be changed while Group Replication is running, and requires a full reboot of the group (a bootstrap by a server with group_replication_bootstrap_group=ON) in order for the value change to take effect.

group_replication_exit_state_action

Configures how Group Replication behaves when a server instance leaves the group unintentionally, for example after encountering an applier error, or in the case of a loss of majority, or when another member of the group expels it due to a suspicion timing out. The timeout period for a member to leave the group in the case of a loss of majority is set by the group_replication_unreachable_majority_timeout system variable. Note that an expelled group member does not know that it was expelled until it reconnects to the group, so the specified action is only taken if the member manages to reconnect, or if the member raises a suspicion on itself and expels itself.

When group_replication_exit_state_action is set to ABORT_SERVER, if the member exits the group unintentionally, the instance shuts down MySQL.

When group_replication_exit_state_action is set to READ_ONLY, if the member exits the group unintentionally, the instance switches MySQL to super read only mode (by setting the system variable super_read_only to ON). This setting is the default in MySQL 5.7.

group_replication_flow_control_applier_threshold

Specifies the number of waiting transactions in the applier queue that trigger flow control. This variable can be changed without resetting Group Replication.

group_replication_flow_control_certifier_threshold

Specifies the number of waiting transactions in the certifier queue that trigger flow control. This variable can be changed without resetting Group Replication.

group_replication_flow_control_hold_percent

Defines what percentage of the group quota remains unused to allow a cluster under flow control to catch up on backlog. A value of 0 implies that no part of the quota is reserved for catching up on the work backlog.

group_replication_flow_control_max_quota

Defines the maximum flow control quota of the group, or the maximum available quota for any period while flow control is enabled. A value of 0 implies that there is no maximum quota set. Cannot be smaller than group_replication_flow_control_min_quota and group_replication_flow_control_min_recovery_quota.

group_replication_flow_control_member_quota_percent

Defines the percentage of the quota that a member should assume is available for itself when calculating the quotas. A value of 0 implies that the quota should be split equally between members that were writers in the last period.

group_replication_flow_control_min_quota

Controls the lowest flow control quota that can be assigned to a member, independently of the calculated minimum quota executed in the last period. A value of 0 implies that there is no minimum quota. Cannot be larger than group_replication_flow_control_max_quota.

group_replication_flow_control_min_recovery_quota

Controls the lowest quota that can be assigned to a member because of another recovering member in the group, independently of the calculated minimum quota executed in the last period. A value of 0 implies that there is no minimum quota. Cannot be larger than group_replication_flow_control_max_quota.

group_replication_flow_control_mode

Specifies the mode used for flow control. This variable can be changed without resetting Group Replication.

group_replication_force_members

A list of peer addresses as a comma separated list such as host1:port1,host2:port2. This option is used to force a new group membership, in which the excluded members do not receive a new view and are blocked. (You need to manually kill the excluded servers.) Any invalid host names in the list could cause this action to fail because they could block group membership. For a description of the procedure to follow, see Section 17.5.3, “Network Partitioning”.

You must specify the address or host name and port as they are given in the group_replication_local_address option for each member. For example:

"198.51.100.44:33061,example.org:33061"

After you have used the group_replication_force_members system variable to successfully force a new group membership and unblock the group, ensure that you clear the system variable. group_replication_force_members must be empty in order to issue a START GROUP_REPLICATION statement.

group_replication_group_name

The name of the group which this server instance belongs to. Must be a valid UUID. This UUID is used internally when setting GTIDs for Group Replication events in the binary log.

group_replication_group_seeds

A list of group members to which a joining member can connect to obtain details of all the current group members. The joining member uses these details to select and connect to a group member to obtain the data needed for synchrony with the group. The list consists of the seed member's network addresses specified as a comma separated list, such as host1:port1,host2:port2.

Note that the value you specify for this variable is not validated until a START GROUP_REPLICATION statement is issued and the Group Communication System (GCS) is available.

Usually this list consists of all members of the group, but you can choose a subset of the group members to be seeds. The list must contain at least one valid member address. Each address is validated when starting Group Replication. If the list does not contain any valid host names, issuing START GROUP_REPLICATION fails.

group_replication_gtid_assignment_block_size

The number of consecutive GTIDs that are reserved for each member. Each member consumes its blocks and reserves more when needed.

This system variable is a group-wide configuration setting. It must have the same value on all group members, cannot be changed while Group Replication is running, and requires a full reboot of the group (a bootstrap by a server with group_replication_bootstrap_group=ON) in order for the value change to take effect.

group_replication_ip_whitelist

Specifies the allowlist of hosts that are permitted to connect to the group. The address that you specify for each group member in group_replication_local_address must be allowlisted on the other servers in the replication group. Note that the value you specify for this variable is not validated until a START GROUP_REPLICATION statement is issued and the Group Communication System (GCS) is available.

By default, this system variable is set to AUTOMATIC, which permits connections from private subnetworks active on the host. The group communication engine (XCom) automatically scans active interfaces on the host, and identifies those with addresses on private subnetworks. These addresses and the localhost IP address for IPv4 are used to create the Group Replication allowlist. For a list of the ranges from which addresses are automatically allowlisted, see Section 17.6.1, “Group Replication IP Address Allowlisting”.

The automatic allowlist of private addresses cannot be used for connections from servers outside the private network. For Group Replication connections between server instances that are on different machines, you must provide public IP addresses and specify these as an explicit allowlist. If you specify any entries for the allowlist, the private addresses are not added automatically, so if you use any of these, you must specify them explicitly. The localhost IP address is added automatically.

As the value of the group_replication_ip_whitelist option, you can specify any combination of the following:

IPv6 addresses, and host names that resolve to IPv6 addresses, are not supported in MySQL 5.7. You can use CIDR notation in combination with host names or IP addresses to allowlist a block of IP addresses with a particular network prefix, but do ensure that all the IP addresses in the specified subnet are under your control.

A comma must separate each entry in the allowlist. For example:

192.0.2.22,198.51.100.0/24,example.org,www.example.com/24

It is possible to configure different allowlists on different group members according to your security requirements, for example, in order to keep different subnets separate. However, this can cause issues when a group is reconfigured. If you do not have a specific security requirement to do otherwise, use the same allowlist on all members of a group. For more details, see Section 17.6.1, “Group Replication IP Address Allowlisting”.

For host names, name resolution takes place only when a connection request is made by another server. A host name that cannot be resolved is not considered for allowlist validation, and a warning message is written to the error log. Forward-confirmed reverse DNS (FCrDNS) verification is carried out for resolved host names.

group_replication_local_address

The network address which the member provides for connections from other members, specified as a host:port formatted string. This address must be reachable by all members of the group because it is used by the group communication engine for Group Replication (XCom, a Paxos variant) for TCP communication between remote XCom instances. Communication with the local instance is over an input channel using shared memory.

Other Group Replication members contact this member through this host:port for all internal group communication. This is not the MySQL server SQL protocol host and port.

The address or host name that you specify in group_replication_local_address is used by Group Replication as the unique identifier for a group member within the replication group. You can use the same port for all members of a replication group as long as the host names or IP addresses are all different, and you can use the same host name or IP address for all members as long as the ports are all different. The recommended port for group_replication_local_address is 33061. Note that the value you specify for this variable is not validated until the START GROUP_REPLICATION statement is issued and the Group Communication System (GCS) is available.

group_replication_member_weight

A percentage weight that can be assigned to members to influence the chance of the member being elected as primary in the event of failover, for example when the existing primary leaves a single-primary group. Assign numeric weights to members to ensure that specific members are elected, for example during scheduled maintenance of the primary or to ensure certain hardware is prioritized in the event of failover.

For a group with members configured as follows:

during election of a new primary the members above would be sorted as member-2, member-3, member-4, and member-1. This results in member-2 being chosen as the new primary in the event of failover. For more information, see Section 17.5.1.1, “Single-Primary Mode”.

group_replication_poll_spin_loops

The number of times the group communication thread waits for the communication engine mutex to be released before the thread waits for more incoming network messages.

group_replication_recovery_complete_at

Recovery policies when handling cached transactions after state transfer. This option specifies whether a member is marked online after it has received all transactions that it missed before it joined the group (TRANSACTIONS_CERTIFIED) or after it has received and applied them (TRANSACTIONS_APPLIED).

group_replication_recovery_retry_count

The number of times that the member that is joining tries to connect to the available donors before giving up.

group_replication_recovery_reconnect_interval

The sleep time, in seconds, between reconnection attempts when no donor was found in the group.

group_replication_recovery_ssl_ca

The path to a file that contains a list of trusted SSL certificate authorities.

group_replication_recovery_ssl_capath

The path to a directory that contains trusted SSL certificate authority certificates.

group_replication_recovery_ssl_cert

The name of the SSL certificate file to use for establishing a secure connection.

group_replication_recovery_ssl_key

The name of the SSL key file to use for establishing a secure connection.

group_replication_recovery_ssl_cipher

The list of permissible ciphers for SSL encryption.

group_replication_recovery_ssl_crl

The path to a directory that contains files containing certificate revocation lists.

group_replication_recovery_ssl_crlpath

The path to a directory that contains files containing certificate revocation lists.

group_replication_recovery_ssl_verify_server_cert

Make the recovery process check the server's Common Name value in the donor sent certificate.

group_replication_recovery_use_ssl

Whether Group Replication recovery connection should use SSL or not.

group_replication_single_primary_mode

group_replication_single_primary_mode instructs the group to pick a single server automatically to be the one that handles read/write workload. This server is the primary and all others are secondaries.

This system variable is a group-wide configuration setting. It must have the same value on all group members, cannot be changed while Group Replication is running, and requires a full reboot of the group (a bootstrap by a server with group_replication_bootstrap_group=ON) in order for the value change to take effect. For instructions to safely bootstrap a group where transactions have been executed and certified, see Section 17.5.4, “Restarting a Group”.

If the group has a value set for this system variable, and a joining member has a different value set for the system variable, the joining member cannot join the group until the value is changed to match. If the group members have a value set for this system variable, and the joining member does not support the system variable, it cannot join the group.

Setting this variable ON causes any setting for group_replication_auto_increment_increment to be ignored.

group_replication_ssl_mode

Specifies the security state of the connection between Group Replication members.

group_replication_start_on_boot

Whether the server should start Group Replication or not during server start.

group_replication_transaction_size_limit

Configures the maximum transaction size in bytes which the replication group accepts. Transactions larger than this size are rolled back by the receiving member and are not broadcast to the group. Large transactions can cause problems for a replication group in terms of memory allocation, which can cause the system to slow down, or in terms of network bandwidth consumption, which can cause a member to be suspected of having failed because it is busy processing the large transaction.

When this system variable is set to 0, there is no limit to the size of transactions the group accepts. In releases up to and including MySQL 5.7.37, the default setting for this system variable is 0. From MySQL 5.7.38, and in MySQL 8.0, the default setting is 150000000 bytes (approximately 143 MB). Adjust the value of this system variable depending on the maximum message size that you need the group to tolerate, bearing in mind that the time taken to process a transaction is proportional to its size. The value of group_replication_transaction_size_limit should be the same on all group members. For further mitigation strategies for large transactions, see Section 17.3.2, “Group Replication Limitations”.

group_replication_unreachable_majority_timeout

Configures how long members that suffer a network partition and cannot connect to the majority wait before leaving the group.

In a group of 5 servers (S1,S2,S3,S4,S5), if there is a disconnection between (S1,S2) and (S3,S4,S5) there is a network partition. The first group (S1,S2) is now in a minority because it cannot contact more than half of the group. While the majority group (S3,S4,S5) remains running, the minority group waits for the specified time for a network reconnection. Any transactions processed by the minority group are blocked until Group Replication is stopped using STOP GROUP REPLICATION on the members of the minority. Note that group_replication_unreachable_majority_timeout has no effect if it is set on the servers in the minority group after the loss of majority has been detected.

By default, this system variable is set to 0, which means that members that find themselves in a minority due to a network partition wait forever to leave the group. If configured to a number of seconds, members wait for this amount of time after losing contact with the majority of members before leaving the group. When the specified time elapses, all pending transactions processed by the minority are rolled back, and the servers in the minority partition move to the ERROR state. These servers then follow the action specified by the system variable group_replication_exit_state_action, which can be to set themselves to super read only mode or shut down MySQL.