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MySQL 5.7 Reference Manual  /  Group Replication  /  Group Replication System Variables

17.6 Group Replication System Variables

These are the system variables that are specific to the Group Replication plugin. Every configuration option is prefixed with "group_replication".

Important

Although most variables are described as dynamic and can be changed while the server is running, most changes only take effect upon restarting the Group Replication plugin. Variables which can be changed without requiring a restart of the plugin are specifically noted as such in this section.

  • group_replication_allow_local_disjoint_gtids_join

    Property Value
    Command-Line Format --group-replication-allow-local-disjoint-gtids-join=value
    Introduced 5.7.17
    Deprecated 5.7.21
    System Variable group_replication_allow_local_disjoint_gtids_join
    Scope Global
    Dynamic Yes
    Type boolean
    Default Value OFF

    Deprecated in version 5.7.21 and scheduled for removal in a future version. Allow the current server to join the group even if it has transactions not present in the group.

    Warning

    Use caution when enabling this option as incorrect usage could lead to inconsistencies in the group.

  • group_replication_allow_local_lower_version_join

    Property Value
    Command-Line Format --group-replication-allow-local-lower-version-join=value
    Introduced 5.7.17
    System Variable group_replication_allow_local_lower_version_join
    Scope Global
    Dynamic Yes
    Type boolean
    Default Value OFF

    Allow the current server to join the group even if it has a lower plugin version than the group.

  • group_replication_auto_increment_increment

    Property Value
    Command-Line Format --group-replication-auto-increment-increment=value
    Introduced 5.7.17
    System Variable group_replication_auto_increment_increment
    Scope Global
    Dynamic Yes
    Type integer
    Default Value 7
    Minimum Value 1
    Maximum Value 65535

    Determines the interval between successive column values for transactions that execute on this server instance.

  • group_replication_bootstrap_group

    Property Value
    Command-Line Format --group-replication-bootstrap-group=value
    Introduced 5.7.17
    System Variable group_replication_bootstrap_group
    Scope Global
    Dynamic Yes
    Type boolean
    Default Value OFF

    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

    Property Value
    Command-Line Format --group-replication-components-stop-timeout=value
    Introduced 5.7.17
    System Variable group_replication_components_stop_timeout
    Scope Global
    Dynamic Yes
    Type integer
    Default Value 31536000

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

  • group_replication_compression_threshold

    Property Value
    Command-Line Format --group-replication-compression-threshold=value
    Introduced 5.7.17
    System Variable group_replication_compression_threshold
    Scope Global
    Dynamic Yes
    Type integer
    Default Value 1000000
    Minimum Value 0
    Maximum Value 4294967296

    The value in bytes above which (LZ4) compression is enforced. When set to zero, deactivates compression.

  • group_replication_enforce_update_everywhere_checks

    Property Value
    Command-Line Format --group-replication-enforce-update-everywhere-checks=value
    Introduced 5.7.17
    System Variable group_replication_enforce_update_everywhere_checks
    Scope Global
    Dynamic Yes
    Type boolean
    Default Value OFF

    Enable or disable strict consistency checks for multi-primary update everywhere.

  • group_replication_flow_control_applier_threshold

    Property Value
    Command-Line Format --group-replication-flow-control-applier-threshold=value
    Introduced 5.7.17
    System Variable group_replication_flow_control_applier_threshold
    Scope Global
    Dynamic Yes
    Type integer
    Default Value 25000
    Minimum Value 0
    Maximum Value 2147483648

    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

    Property Value
    Command-Line Format --group-replication-flow-control-certifier-threshold=value
    Introduced 5.7.17
    System Variable group_replication_flow_control_certifier_threshold
    Scope Global
    Dynamic Yes
    Type integer
    Default Value 25000
    Minimum Value 0
    Maximum Value 2147483648

    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_mode

    Property Value
    Command-Line Format --group-replication-flow-control-mode=value
    Introduced 5.7.17
    System Variable group_replication_flow_control_mode
    Scope Global
    Dynamic Yes
    Type enumeration
    Default Value QUOTA
    Valid Values

    DISABLED

    QUOTA

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

  • group_replication_force_members

    Property Value
    Command-Line Format --group-replication-force-members=value
    Introduced 5.7.17
    System Variable group_replication_force_members
    Scope Global
    Dynamic Yes
    Type string

    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 subsequent START GROUP_REPLICATION statements to fail because they could block group membership.

  • group_replication_group_name

    Property Value
    Command-Line Format --group-replication-group-name=value
    Introduced 5.7.17
    System Variable group_replication_group_name
    Scope Global
    Dynamic Yes
    Type string

    The name of the group which this server instance belongs to. Must be a valid UUID.

  • group_replication_group_seeds

    Property Value
    Command-Line Format --group-replication-group-seeds=value
    Introduced 5.7.17
    System Variable group_replication_group_seeds
    Scope Global
    Dynamic Yes
    Type string

    A list of group members that provide a member which joins the group with the data required for the joining member to gain 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. Ususally 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_ip_whitelist

    Property Value
    Command-Line Format --group-replication-ip-whitelist=value
    Introduced 5.7.17
    System Variable group_replication_ip_whitelist
    Scope Global
    Dynamic Yes
    Type string
    Default Value AUTOMATIC

    Specifies which hosts are permitted to connect to the group. By default, this system variable is set to AUTOMATIC, which permits connections from private subnetworks active on the host. Active interfaces on the host are scanned and those with addresses on private subnetworks are automatically added to the permitted list.

    Alternatively, you can specify a whitelist of permitted hosts as a comma separated list of IPv4 addresses, subnet CIDR notation, or (from MySQL 5.7.21) host names, in any combination. For example:

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

    Address 127.0.0.1 is always permitted to connect, even when not specified explicitly. IPv6 addresses, and host names that resolve to IPv6 addresses, are not supported.

    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 whitelist validation, and a warning message is written to the error log. Forward-confirmed reverse DNS (FCrDNS) verification is carried out for resolved host names.

    Warning

    Host names are inherently less secure than IP addresses in a whitelist. FCrDNS verification provides a good level of protection, but can be compromised by certain types of attack. Specify host names in your whitelist only when strictly necessary, and ensure that all components used for name resolution, such as DNS servers, are maintained under your control. You can also implement name resolution locally using the hosts file, to avoid the use of external components.

  • group_replication_local_address

    Property Value
    Command-Line Format --group-replication-local-address=value
    Introduced 5.7.17
    System Variable group_replication_local_address
    Scope Global
    Dynamic Yes
    Type string

    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 XCOM, the internal group communication system.

    Warning

    Do not use this address for communication with the member.

    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.

  • group_replication_member_weight

    Property Value
    Command-Line Format --group-replication-member-weight=value
    Introduced 5.7.20
    System Variable group_replication_member_weight
    Scope Global
    Dynamic Yes
    Type integer
    Default Value 50
    Minimum Value 0
    Maximum Value 100

    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:

    • member-1: group_replication_member_weight=30, server_uuid=aaaa

    • member-2: group_replication_member_weight=40, server_uuid=bbbb

    • member-3: group_replication_member_weight=40, server_uuid=cccc

    • member-4: group_replication_member_weight=40, server_uuid=dddd

    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 17.4.1.1, “Single-Primary Mode”.

  • group_replication_poll_spin_loops

    Property Value
    Command-Line Format --group-replication-poll-spin-loops=value
    Introduced 5.7.17
    System Variable group_replication_poll_spin_loops
    Scope Global
    Dynamic Yes
    Type (64-bit platforms) integer
    Type (32-bit platforms) integer
    Default Value (64-bit platforms) 0
    Default Value (32-bit platforms) 0
    Minimum Value (64-bit platforms) 0
    Minimum Value (32-bit platforms) 0
    Maximum Value (64-bit platforms) 18446744073709547520
    Maximum Value (32-bit platforms) 4294967295

    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_retry_count

    Property Value
    Command-Line Format --group-replication-recovery-retry-count=value
    Introduced 5.7.17
    System Variable group_replication_recovery_retry_count
    Scope Global
    Dynamic Yes
    Type integer
    Default Value 10
    Minimum Value 0
    Maximum Value 31536000

    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

    Property Value
    Command-Line Format --group-replication-recovery-reconnect-interval=value
    Introduced 5.7.17
    System Variable group_replication_recovery_reconnect_interval
    Scope Global
    Dynamic Yes
    Type integer
    Default Value 60
    Minimum Value 0
    Maximum Value 0

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

  • group_replication_recovery_use_ssl

    Property Value
    Command-Line Format --group-replication-recovery-use-ssl=value
    Introduced 5.7.17
    System Variable group_replication_recovery_use_ssl
    Scope Global
    Dynamic Yes
    Type boolean
    Default Value OFF

    Whether Group Replication recovery connection should use SSL or not.

  • group_replication_recovery_ssl_ca

    Property Value
    Command-Line Format --group-replication-recovery-ssl-ca=value
    Introduced 5.7.17
    System Variable group_replication_recovery_ssl_ca
    Scope Global
    Dynamic Yes
    Type string

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

  • group_replication_recovery_ssl_capath

    Property Value
    Command-Line Format --group-replication-recovery-ssl-capath=value
    Introduced 5.7.17
    System Variable group_replication_recovery_ssl_capath
    Scope Global
    Dynamic Yes
    Type string

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

  • group_replication_recovery_ssl_cert

    Property Value
    Command-Line Format --group-replication-recovery-ssl-cert=value
    Introduced 5.7.17
    System Variable group_replication_recovery_ssl_cert
    Scope Global
    Dynamic Yes
    Type string

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

  • group_replication_recovery_ssl_key

    Property Value
    Command-Line Format --group-replication-recovery-ssl-key=value
    Introduced 5.7.17
    System Variable group_replication_recovery_ssl_key
    Scope Global
    Dynamic Yes
    Type string

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

  • group_replication_recovery_ssl_cipher

    Property Value
    Command-Line Format --group-replication-recovery-ssl-cipher=value
    Introduced 5.7.17
    System Variable group_replication_recovery_ssl_cipher
    Scope Global
    Dynamic Yes
    Type string

    The list of permitted ciphers for SSL encryption.

  • group_replication_recovery_ssl_crl

    Property Value
    Command-Line Format --group-replication-recovery-ssl-crl=value
    Introduced 5.7.17
    System Variable group_replication_recovery_ssl_crl
    Scope Global
    Dynamic Yes
    Type string

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

  • group_replication_recovery_ssl_crlpath

    Property Value
    Command-Line Format --group-replication-recovery-ssl-crlpath=value
    Introduced 5.7.17
    System Variable group_replication_recovery_ssl_crlpath
    Scope Global
    Dynamic Yes
    Type string

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

  • group_replication_recovery_ssl_verify_server_cert

    Property Value
    Command-Line Format --group-replication-recovery-ssl-verify-server-cert=value
    Introduced 5.7.17
    System Variable group_replication_recovery_ssl_verify_server_cert
    Scope Global
    Dynamic Yes
    Type boolean
    Default Value OFF

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

  • group_replication_recovery_complete_at

    Property Value
    Command-Line Format --group-replication-recovery-complete-at=value
    Introduced 5.7.17
    System Variable group_replication_recovery_complete_at
    Scope Global
    Dynamic Yes
    Type enumeration
    Default Value TRANSACTIONS_APPLIED
    Valid Values

    TRANSACTIONS_CERTIFIED

    TRANSACTIONS_APPLIED

    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_gtid_assignment_block_size

    Property Value
    Command-Line Format --group-replication-gtid-assignment-block-size=value
    Introduced 5.7.17
    System Variable group_replication_gtid_assignment_block_size
    Scope Global
    Dynamic Yes
    Type (64-bit platforms) integer
    Type (32-bit platforms) integer
    Default Value (64-bit platforms) 1000000
    Default Value (32-bit platforms) 1000000
    Minimum Value (64-bit platforms) 1
    Minimum Value (32-bit platforms) 1
    Maximum Value (64-bit platforms) 18446744073709547520
    Maximum Value (32-bit platforms) 4294967295

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

  • group_replication_single_primary_mode

    Property Value
    Command-Line Format --group-replication-single-primary-mode=value
    Introduced 5.7.17
    System Variable group_replication_single_primary_mode
    Scope Global
    Dynamic Yes
    Type boolean
    Default Value ON

    Instructs the group to automatically pick a single server to be the one that handles read/write workload. This server is the PRIMARY and all others are SECONDARIES.

  • group_replication_ssl_mode

    Property Value
    Command-Line Format --group-replication-ssl-mode=value
    Introduced 5.7.17
    System Variable group_replication_ssl_mode
    Scope Global
    Dynamic Yes
    Type enumeration
    Default Value DISABLED
    Valid Values

    DISABLED

    REQUIRED

    VERIFY_CA

    VERIFY_IDENTITY

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

  • group_replication_start_on_boot

    Property Value
    Command-Line Format --group-replication-start-on-boot=value
    Introduced 5.7.17
    System Variable group_replication_start_on_boot
    Scope Global
    Dynamic Yes
    Type boolean
    Default Value ON

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

  • group_replication_transaction_size_limit

    Property Value
    Command-Line Format --group-replication-transaction-size-limit=value
    Introduced 5.7.19
    System Variable group_replication_transaction_size_limit
    Scope Global
    Dynamic Yes
    Type (>= 5.7.19) integer
    Default Value (>= 5.7.19) 0
    Minimum Value (>= 5.7.19) 0
    Maximum Value (>= 5.7.19) 2147483647

    Configures the maximum transaction size in bytes which the group accepts. Transactions larger than this size are rolled back. Use this option to avoid large transactions causing the group to fail. A large transaction can cause problems for a group, either in terms of memory allocation or network bandwidth consumption, which may cause the failure detector to trigger because a given member is unreachable while it is busy processing the large transaction. When set to 0 there is no limit to the size of transactions the group accepts, and there may be the risk of large transactions causing the group to fail. Adjust the value of this variable depending on the size of workload you require from the group.

  • group_replication_unreachable_majority_timeout

    Property Value
    Command-Line Format --group-replication-unreachable-majority-timeout=value
    Introduced 5.7.19
    System Variable group_replication_unreachable_majority_timeout
    Scope Global
    Dynamic Yes
    Type integer
    Default Value 0
    Minimum Value 0
    Maximum Value 31536000

    Configures how long members that suffer a network partition and cannot connect to the majority wait before leaving the group. By default set to 0, which means that members that find themselves in a minority due to a network partition wait forever to connect 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 forever 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.

    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. All pending transactions processed by the minority are rolled back and the servers in the minority partition move to the ERROR state and set themselves to super_read_only=ON mode.

    Warning

    When you have a symmetric group, with just two members for example (S0,S2), if there is a network partition and there is no majority, after the configured timeout all members shut down and enter ERROR state.


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