MySQL 5.7 Release Notes
This section lists the system variables that are specific to the Group Replication plugin.
The name of each Group Replication system variable is prefixed
with group_replication_.
Most system variables for Group Replication are described as
dynamic, and their values can be changed while the server is
running. However, in most cases, the change only takes effect
after you stop and restart Group Replication on the group member
using a STOP GROUP_REPLICATION
statement followed by a START
GROUP_REPLICATION statement. Changes to the following
system variables take effect without stopping and restarting Group
Replication:
Most system variables for Group Replication can have different values on different group members. For the following system variables, it is advisable to set the same value on all members of a group in order to avoid unnecessary rollback of transactions, failure of message delivery, or failure of message recovery:
Some system variables on a Group Replication group member,
including some Group Replication-specific system variables and
some general system variables, are group-wide configuration
settings. These system variables must have the same value on all
group members, cannot be changed while Group Replication is
running, and require 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. These conditions
apply to the following system variables:
Important
A number of system variables for Group Replication are not completely validated during server startup if they are passed as command line arguments to the server. These system variables include
group_replication_group_name,group_replication_single_primary_mode,group_replication_force_members, the SSL variables, and the flow control system variables. They are only fully validated after the server has started.System variables for Group Replication that specify IP addresses or host names for group members are not validated until a
START GROUP_REPLICATIONstatement is issued. Group Replication's Group Communication System (GCS) is not available to validate the values until that point.
The system variables that are specific to the Group Replication plugin are as follows:
group_replication_allow_local_disjoint_gtids_joinCommand-Line Format --group-replication-allow-local-disjoint-gtids-join[={OFF|ON}]Introduced 5.7.17 Deprecated 5.7.21 System Variable group_replication_allow_local_disjoint_gtids_joinScope Global Dynamic Yes Type Boolean Default Value OFFDeprecated 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.
WarningUse caution when enabling this option as incorrect usage can lead to conflicts in the group and rollback of transactions. The option should only be enabled as a last resort method to allow a server that has local transactions to join an existing group, and then only if the local transactions do not affect the data that is handled by the group (for example, an administrative action that was written to the binary log). The option should not be left enabled on all group members.
group_replication_allow_local_lower_version_joinCommand-Line Format --group-replication-allow-local-lower-version-join[={OFF|ON}]Introduced 5.7.17 System Variable group_replication_allow_local_lower_version_joinScope Global Dynamic Yes Type Boolean Default Value OFFAllows 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. Setgroup_replication_allow_local_lower_version_jointoONonly in the following scenarios:A server must be added to the group in an emergency in order to improve the group's fault tolerance, and only older versions are available.
You want to carry out a downgrade of the replication group members without shutting down the whole group and bootstrapping it again.
WarningSetting this option to
ONdoes not make the new member compatible with the group, and allows it to join the group without any safeguards against incompatible behaviors by the existing members. To ensure the new member's correct operation, take both of the following precautions:Before the server with the lower major version joins the group, stop all writes on that server.
From the point where the server with the lower major version joins the group, stop all writes on the other servers in the group.
Without these precautions, the server with the lower major version is likely to experience difficulties and terminate with an error.
group_replication_auto_increment_incrementCommand-Line Format --group-replication-auto-increment-increment=#Introduced 5.7.17 System Variable group_replication_auto_increment_incrementScope Global Dynamic Yes Type Integer Default Value 7Minimum Value 1Maximum Value 65535Determines 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_incrementis changed to this value, and the value of the server system variableauto_increment_offsetis 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 ifauto_increment_incrementandauto_increment_offseteach 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.
ImportantSetting
group_replication_auto_increment_incrementhas no effect whengroup_replication_single_primary_modeisON.group_replication_bootstrap_groupCommand-Line Format --group-replication-bootstrap-group[={OFF|ON}]Introduced 5.7.17 System Variable group_replication_bootstrap_groupScope Global Dynamic Yes Type Boolean Default Value OFFConfigure 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 toOFFboth 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_timeoutCommand-Line Format --group-replication-components-stop-timeout=#Introduced 5.7.17 System Variable group_replication_components_stop_timeoutScope Global Dynamic Yes Type Integer Default Value 31536000Minimum Value 2Maximum Value 31536000Unit seconds Timeout, in seconds, that Group Replication waits for each of the components when shutting down.
group_replication_compression_thresholdCommand-Line Format --group-replication-compression-threshold=#Introduced 5.7.17 System Variable group_replication_compression_thresholdScope Global Dynamic Yes Type Integer Default Value 1000000Minimum Value 0Maximum Value 4294967295Unit bytes 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_thresholdshould 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_thresholdsystem 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 forgroup_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_checksCommand-Line Format --group-replication-enforce-update-everywhere-checks[={OFF|ON}]Introduced 5.7.17 System Variable group_replication_enforce_update_everywhere_checksScope Global Dynamic Yes Type Boolean Default Value OFFEnable 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:
If a transaction is executed under the
SERIALIZABLEisolation level, then its commit fails when synchronizing itself with the group.If a transaction executes against a table that has foreign keys with cascading constraints, then the transaction fails to commit when synchronizing itself with the group.
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_actionCommand-Line Format --group-replication-exit-state-action=valueIntroduced 5.7.24 System Variable group_replication_exit_state_actionScope Global Dynamic Yes Type Enumeration Default Value READ_ONLYValid Values ABORT_SERVERREAD_ONLYConfigures 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_timeoutsystem 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_actionis set toABORT_SERVER, if the member exits the group unintentionally, the instance shuts down MySQL.When
group_replication_exit_state_actionis set toREAD_ONLY, if the member exits the group unintentionally, the instance switches MySQL to super read only mode (by setting the system variablesuper_read_onlytoON). This setting is the default in MySQL 5.7.ImportantIf a failure occurs before the member has successfully joined the group, the specified exit action is not taken. This is the case if there is a failure during the local configuration check, or a mismatch between the configuration of the joining member and the configuration of the group. In these situations, the
super_read_onlysystem variable is left with its original value, and the server does not shut down MySQL. To ensure that the server cannot accept updates when Group Replication did not start, we therefore recommend thatsuper_read_only=ONis set in the server's configuration file at startup, which Group Replication changes toOFFon primary members after it has been started successfully. This safeguard is particularly important when the server is configured to start Group Replication on server boot (group_replication_start_on_boot=ON), but it is also useful when Group Replication is started manually using aSTART GROUP_REPLICATIONcommand.If a failure occurs after the member has successfully joined the group, the specified exit action is taken. This is the case if there is an applier error, if the member is expelled from the group, or if the member is set to time out in the event of an unreachable majority. In these situations, if
READ_ONLYis the exit action, thesuper_read_onlysystem variable is set toON, or ifABORT_SERVERis the exit action, the server shuts down MySQL.Table 17.5 Exit actions in Group Replication failure situations
Failure situation
Group Replication started with
START GROUP_REPLICATIONGroup Replication started with
group_replication_start_on_boot =ONMember fails local configuration check
OR
Mismatch between joining member and group configuration
super_read_onlyunchangedMySQL continues running
Set
super_read_only=ONat startup to prevent updatessuper_read_onlyunchangedMySQL continues running
Set
super_read_only=ONat startup to prevent updates (Important)Applier error on member
OR
Member expelled from group
OR
Unreachable majority timeout
super_read_onlyset toONOR
MySQL shuts down
super_read_onlyset toONOR
MySQL shuts down
group_replication_flow_control_applier_thresholdCommand-Line Format --group-replication-flow-control-applier-threshold=#Introduced 5.7.17 System Variable group_replication_flow_control_applier_thresholdScope Global Dynamic Yes Type Integer Default Value 25000Minimum Value 0Maximum Value 2147483647Unit transactions 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_thresholdCommand-Line Format --group-replication-flow-control-certifier-threshold=#Introduced 5.7.17 System Variable group_replication_flow_control_certifier_thresholdScope Global Dynamic Yes Type Integer Default Value 25000Minimum Value 0Maximum Value 2147483647Unit transactions 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_percentCommand-Line Format --group-replication-flow-control-hold-percent=#System Variable group_replication_flow_control_hold_percentScope Global Dynamic Yes Type Integer Default Value 10Minimum Value 0Maximum Value 100Unit percentage 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_quotaCommand-Line Format --group-replication-flow-control-max-quota=#System Variable group_replication_flow_control_max_quotaScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Maximum Value 2147483647Defines 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_quotaandgroup_replication_flow_control_min_recovery_quota.group_replication_flow_control_member_quota_percentCommand-Line Format --group-replication-flow-control-member-quota-percent=#System Variable group_replication_flow_control_member_quota_percentScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Maximum Value 100Unit percentage 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_quotaCommand-Line Format --group-replication-flow-control-min-quota=#System Variable group_replication_flow_control_min_quotaScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Maximum Value 2147483647Controls 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_quotaCommand-Line Format --group-replication-flow-control-min-recovery-quota=#System Variable group_replication_flow_control_min_recovery_quotaScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Maximum Value 2147483647Controls 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_modeCommand-Line Format --group-replication-flow-control-mode=valueIntroduced 5.7.17 System Variable group_replication_flow_control_modeScope Global Dynamic Yes Type Enumeration Default Value QUOTAValid Values DISABLEDQUOTASpecifies the mode used for flow control. This variable can be changed without resetting Group Replication.
group_replication_force_membersCommand-Line Format --group-replication-force-members=valueIntroduced 5.7.17 System Variable group_replication_force_membersScope 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 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_addressoption for each member. For example:"198.51.100.44:33061,example.org:33061"After you have used the
group_replication_force_memberssystem variable to successfully force a new group membership and unblock the group, ensure that you clear the system variable.group_replication_force_membersmust be empty in order to issue aSTART GROUP_REPLICATIONstatement.-
Command-Line Format --group-replication-group-name=valueIntroduced 5.7.17 System Variable group_replication_group_nameScope Global Dynamic Yes Type String 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.
ImportantA unique UUID must be used.
-
Command-Line Format --group-replication-group-seeds=valueIntroduced 5.7.17 System Variable group_replication_group_seedsScope Global Dynamic Yes Type String 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.ImportantThese addresses must not be the member's SQL hostname and port.
Note that the value you specify for this variable is not validated until a
START GROUP_REPLICATIONstatement 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_REPLICATIONfails. group_replication_gtid_assignment_block_sizeCommand-Line Format --group-replication-gtid-assignment-block-size=#Introduced 5.7.17 System Variable group_replication_gtid_assignment_block_sizeScope Global Dynamic Yes Type Integer Default Value 1000000Minimum Value 1Maximum Value (64-bit platforms) 9223372036854775807Maximum Value (32-bit platforms) 4294967295The 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_whitelistCommand-Line Format --group-replication-ip-whitelist=valueIntroduced 5.7.17 System Variable group_replication_ip_whitelistScope Global Dynamic Yes Type String Default Value AUTOMATICSpecifies 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_addressmust be allowlisted on the other servers in the replication group. Note that the value you specify for this variable is not validated until aSTART GROUP_REPLICATIONstatement 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 thelocalhostIP 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
localhostIP address is added automatically.As the value of the
group_replication_ip_whitelistoption, you can specify any combination of the following:IPv4 addresses (for example,
198.51.100.44)IPv4 addresses with CIDR notation (for example,
192.0.2.21/24)Host names, from MySQL 5.7.21 (for example,
example.org)Host names with CIDR notation, from MySQL 5.7.21 (for example,
www.example.com/24)
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/24It 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.
WarningHost names are inherently less secure than IP addresses in an allowlist. FCrDNS verification provides a good level of protection, but can be compromised by certain types of attack. Specify host names in your allowlist 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_addressCommand-Line Format --group-replication-local-address=valueIntroduced 5.7.17 System Variable group_replication_local_addressScope Global Dynamic Yes Type String The network address which the member provides for connections from other members, specified as a
host:portformatted 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.WarningDo not use this address for communication with the member.
Other Group Replication members contact this member through this
host:portfor 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_addressis 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 forgroup_replication_local_addressis 33061. Note that the value you specify for this variable is not validated until theSTART GROUP_REPLICATIONstatement is issued and the Group Communication System (GCS) is available.group_replication_member_weightCommand-Line Format --group-replication-member-weight=#Introduced 5.7.20 System Variable group_replication_member_weightScope Global Dynamic Yes Type Integer Default Value 50Minimum Value 0Maximum Value 100Unit percentage 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=aaaamember-2: group_replication_member_weight=40, server_uuid=bbbbmember-3: group_replication_member_weight=40, server_uuid=ccccmember-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, andmember-1. This results inmember-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_loopsCommand-Line Format --group-replication-poll-spin-loops=#Introduced 5.7.17 System Variable group_replication_poll_spin_loopsScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Maximum Value (64-bit platforms) 18446744073709551615Maximum Value (32-bit platforms) 4294967295The 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_atCommand-Line Format --group-replication-recovery-complete-at=valueIntroduced 5.7.17 System Variable group_replication_recovery_complete_atScope Global Dynamic Yes Type Enumeration Default Value TRANSACTIONS_APPLIEDValid Values TRANSACTIONS_CERTIFIEDTRANSACTIONS_APPLIEDRecovery 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_countCommand-Line Format --group-replication-recovery-retry-count=#Introduced 5.7.17 System Variable group_replication_recovery_retry_countScope Global Dynamic Yes Type Integer Default Value 10Minimum Value 0Maximum Value 31536000The number of times that the member that is joining tries to connect to the available donors before giving up.
group_replication_recovery_reconnect_intervalCommand-Line Format --group-replication-recovery-reconnect-interval=#Introduced 5.7.17 System Variable group_replication_recovery_reconnect_intervalScope Global Dynamic Yes Type Integer Default Value 60Minimum Value 0Maximum Value 31536000Unit seconds The sleep time, in seconds, between reconnection attempts when no donor was found in the group.
group_replication_recovery_ssl_caCommand-Line Format --group-replication-recovery-ssl-ca=valueIntroduced 5.7.17 System Variable group_replication_recovery_ssl_caScope Global Dynamic Yes Type String The path to a file that contains a list of trusted SSL certificate authorities.
group_replication_recovery_ssl_capathCommand-Line Format --group-replication-recovery-ssl-capath=valueIntroduced 5.7.17 System Variable group_replication_recovery_ssl_capathScope Global Dynamic Yes Type String The path to a directory that contains trusted SSL certificate authority certificates.
group_replication_recovery_ssl_certCommand-Line Format --group-replication-recovery-ssl-cert=valueIntroduced 5.7.17 System Variable group_replication_recovery_ssl_certScope Global Dynamic Yes Type String The name of the SSL certificate file to use for establishing a secure connection.
group_replication_recovery_ssl_keyCommand-Line Format --group-replication-recovery-ssl-key=valueIntroduced 5.7.17 System Variable group_replication_recovery_ssl_keyScope Global Dynamic Yes Type String The name of the SSL key file to use for establishing a secure connection.
group_replication_recovery_ssl_cipherCommand-Line Format --group-replication-recovery-ssl-cipher=valueIntroduced 5.7.17 System Variable group_replication_recovery_ssl_cipherScope Global Dynamic Yes Type String The list of permissible ciphers for SSL encryption.
group_replication_recovery_ssl_crlCommand-Line Format --group-replication-recovery-ssl-crl=valueIntroduced 5.7.17 System Variable group_replication_recovery_ssl_crlScope Global Dynamic Yes Type File name The path to a directory that contains files containing certificate revocation lists.
group_replication_recovery_ssl_crlpathCommand-Line Format --group-replication-recovery-ssl-crlpath=valueIntroduced 5.7.17 System Variable group_replication_recovery_ssl_crlpathScope Global Dynamic Yes Type Directory name The path to a directory that contains files containing certificate revocation lists.
group_replication_recovery_ssl_verify_server_certCommand-Line Format --group-replication-recovery-ssl-verify-server-cert[={OFF|ON}]Introduced 5.7.17 System Variable group_replication_recovery_ssl_verify_server_certScope Global Dynamic Yes Type Boolean Default Value OFFMake the recovery process check the server's Common Name value in the donor sent certificate.
group_replication_recovery_use_sslCommand-Line Format --group-replication-recovery-use-ssl[={OFF|ON}]Introduced 5.7.17 System Variable group_replication_recovery_use_sslScope Global Dynamic Yes Type Boolean Default Value OFFWhether Group Replication recovery connection should use SSL or not.
group_replication_single_primary_modeCommand-Line Format --group-replication-single-primary-mode[={OFF|ON}]Introduced 5.7.17 System Variable group_replication_single_primary_modeScope Global Dynamic Yes Type Boolean Default Value ONNoteThis system variable is a group-wide configuration setting, and a full reboot of the replication group is required for a change to take effect.
group_replication_single_primary_modeinstructs 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
ONcauses any setting forgroup_replication_auto_increment_incrementto be ignored.-
Command-Line Format --group-replication-ssl-mode=valueIntroduced 5.7.17 System Variable group_replication_ssl_modeScope Global Dynamic Yes Type Enumeration Default Value DISABLEDValid Values DISABLEDREQUIREDVERIFY_CAVERIFY_IDENTITYSpecifies the security state of the connection between Group Replication members.
group_replication_start_on_bootCommand-Line Format --group-replication-start-on-boot[={OFF|ON}]Introduced 5.7.17 System Variable group_replication_start_on_bootScope Global Dynamic Yes Type Boolean Default Value ONWhether the server should start Group Replication or not during server start.
group_replication_transaction_size_limitCommand-Line Format --group-replication-transaction-size-limit=#Introduced 5.7.19 System Variable group_replication_transaction_size_limitScope Global Dynamic Yes Type Integer Default Value (≥ 5.7.38) 150000000Default Value (≥ 5.7.19, ≤ 5.7.37) 0Minimum Value 0Maximum Value 2147483647Unit bytes 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_limitshould 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_timeoutCommand-Line Format --group-replication-unreachable-majority-timeout=#Introduced 5.7.19 System Variable group_replication_unreachable_majority_timeoutScope Global Dynamic Yes Type Integer Default Value 0Minimum Value 0Maximum Value 31536000Unit seconds 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 REPLICATIONon the members of the minority. Note thatgroup_replication_unreachable_majority_timeouthas 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
ERRORstate. These servers then follow the action specified by the system variablegroup_replication_exit_state_action, which can be to set themselves to super read only mode or shut down MySQL.WarningWhen 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 enter
ERRORstate.