17.7.1 Group Replication System Variables (original) (raw)

17.7.1 Group Replication System Variables

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:

• 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

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:

• group_replication_auto_increment_increment
• group_replication_compression_threshold
• group_replication_transaction_size_limit

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 withgroup_replication_bootstrap_group=ON) in order for the value change to take effect. These conditions apply to the following system variables:

• 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

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 includegroup_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_REPLICATION statement 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_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.
  Warning
  Use 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_join
  Allows the current server to join the group even if it has a lower major version than the group. With the default settingOFF, 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_join to ON only 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.
    Warning
    Setting this option to ON does 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:
  1. Before the server with the lower major version joins the group, stop all writes on that server.
  2. 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_increment

  Command-Line Format	--group-replication-auto-increment-increment=#
  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. 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 variableauto_increment_increment is changed to this value, and the value of the server system variableauto_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 ifauto_increment_increment andauto_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

  Command-Line Format	--group-replication-bootstrap-group[={OFF|ON}]
  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 toOFF. It should be set toOFF 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

  Command-Line Format	--group-replication-components-stop-timeout=#
  Introduced	5.7.17
  System Variable	group_replication_components_stop_timeout
  Scope	Global
  Dynamic	Yes
  Type	Integer
  Default Value	31536000
  Minimum Value	2
  Maximum Value	31536000
  Unit	seconds
  Timeout, in seconds, that Group Replication waits for each of the components when shutting down.

• group_replication_compression_threshold

  Command-Line Format	--group-replication-compression-threshold=#
  Introduced	5.7.17
  System Variable	group_replication_compression_threshold
  Scope	Global
  Dynamic	Yes
  Type	Integer
  Default Value	1000000
  Minimum Value	0
  Maximum Value	4294967295
  Unit	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 ofgroup_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 thegroup_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 forgroup_replication_compression_threshold, because transactions above this size cannot be committed when message compression is enabled.
  For more information, seeSection 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:
  • If a transaction is executed under theSERIALIZABLE isolation 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 withgroup_replication_bootstrap_group=ON) in order for the value change to take effect.
• group_replication_exit_state_action

  Command-Line Format	--group-replication-exit-state-action=value
  Introduced	5.7.24
  System Variable	group_replication_exit_state_action
  Scope	Global
  Dynamic	Yes
  Type	Enumeration
  Default Value	READ_ONLY
  Valid Values	ABORT_SERVERREAD_ONLY
  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 thegroup_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.
  Whengroup_replication_exit_state_action is set to ABORT_SERVER, if the member exits the group unintentionally, the instance shuts down MySQL.
  Whengroup_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 variablesuper_read_only toON). This setting is the default in MySQL 5.7.
  Important
  If 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, thesuper_read_only system 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=ON is set in the server's configuration file at startup, which Group Replication changes to OFF on 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 a START GROUP_REPLICATION command.
  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, ifREAD_ONLY is the exit action, thesuper_read_only system variable is set to ON, or ifABORT_SERVER is 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_REPLICATION
  -------------------------------------------------------------------------------------------------	----------------------------------------------------------------------------------------------------------
  Member fails local configuration check OR Mismatch between joining member and group configuration	super_read_only unchanged MySQL continues running Set super_read_only=ON at startup to prevent updates
  Applier error on member OR Member expelled from group OR Unreachable majority timeout	super_read_only set toON OR MySQL shuts down

• group_replication_flow_control_applier_threshold

  Command-Line Format	--group-replication-flow-control-applier-threshold=#
  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	2147483647
  Unit	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_threshold

  Command-Line Format	--group-replication-flow-control-certifier-threshold=#
  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	2147483647
  Unit	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_percent

  Command-Line Format	--group-replication-flow-control-hold-percent=#
  System Variable	group_replication_flow_control_hold_percent
  Scope	Global
  Dynamic	Yes
  Type	Integer
  Default Value	10
  Minimum Value	0
  Maximum Value	100
  Unit	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_quota

  Command-Line Format	--group-replication-flow-control-max-quota=#
  System Variable	group_replication_flow_control_max_quota
  Scope	Global
  Dynamic	Yes
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	2147483647
  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 thangroup_replication_flow_control_min_quota andgroup_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

  Command-Line Format	--group-replication-flow-control-min-quota=#
  System Variable	group_replication_flow_control_min_quota
  Scope	Global
  Dynamic	Yes
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	2147483647
  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 thangroup_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 thangroup_replication_flow_control_max_quota.
• group_replication_flow_control_mode

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

• group_replication_force_members

  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 ashost1: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, seeSection 17.5.3, “Network Partitioning”.
  You must specify the address or host name and port as they are given in thegroup_replication_local_address option for each member. For example:

"198.51.100.44:33061,example.org:33061"  

After you have used thegroup_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

  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. This UUID is used internally when setting GTIDs for Group Replication events in the binary log.
  Important
  A unique UUID must be used.

• group_replication_group_seeds

  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 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 ashost1:port1,host2:port2.
  Important
  These 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_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, issuingSTART GROUP_REPLICATION fails.

• group_replication_gtid_assignment_block_size

  Command-Line Format	--group-replication-gtid-assignment-block-size=#
  Introduced	5.7.17
  System Variable	group_replication_gtid_assignment_block_size
  Scope	Global
  Dynamic	Yes
  Type	Integer
  Default Value	1000000
  Minimum Value	1
  Maximum Value (64-bit platforms)	9223372036854775807
  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.
  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 withgroup_replication_bootstrap_group=ON) in order for the value change to take effect.

• group_replication_ip_whitelist

  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 the allowlist of hosts that are permitted to connect to the group. The address that you specify for each group member ingroup_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 toAUTOMATIC, 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 thelocalhost IP address for IPv4 are used to create the Group Replication allowlist. For a list of the ranges from which addresses are automatically allowlisted, seeSection 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 thegroup_replication_ip_whitelist option, 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/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, seeSection 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.
Warning
Host 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_address

  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 ahost: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.
  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.
  The address or host name that you specify ingroup_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 forgroup_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

  Command-Line Format	--group-replication-member-weight=#
  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
  Unit	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=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, andmember-1. This results inmember-2 being chosen as the new primary in the event of failover. For more information, seeSection 17.5.1.1, “Single-Primary Mode”.
• group_replication_poll_spin_loops

  Command-Line Format	--group-replication-poll-spin-loops=#
  Introduced	5.7.17
  System Variable	group_replication_poll_spin_loops
  Scope	Global
  Dynamic	Yes
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value (64-bit platforms)	18446744073709551615
  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_complete_at

  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_CERTIFIEDTRANSACTIONS_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_recovery_retry_count

  Command-Line Format	--group-replication-recovery-retry-count=#
  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

  Command-Line Format	--group-replication-recovery-reconnect-interval=#
  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	31536000
  Unit	seconds
  The sleep time, in seconds, between reconnection attempts when no donor was found in the group.

• group_replication_recovery_ssl_ca

  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
  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

  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	File name
  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

  Command-Line Format	--group-replication-recovery-use-ssl[={OFF|ON}]
  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_single_primary_mode

  Command-Line Format	--group-replication-single-primary-mode[={OFF|ON}]
  Introduced	5.7.17
  System Variable	group_replication_single_primary_mode
  Scope	Global
  Dynamic	Yes
  Type	Boolean
  Default Value	ON
  Note
  This 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_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 withgroup_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, seeSection 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 forgroup_replication_auto_increment_increment to be ignored.

• group_replication_ssl_mode

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

• group_replication_start_on_boot

  Command-Line Format	--group-replication-start-on-boot[={OFF|ON}]
  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

  Command-Line Format	--group-replication-transaction-size-limit=#
  Introduced	5.7.19
  System Variable	group_replication_transaction_size_limit
  Scope	Global
  Dynamic	Yes
  Type	Integer
  Default Value (≥ 5.7.38)	150000000
  Default Value (≥ 5.7.19, ≤ 5.7.37)	0
  Minimum Value	0
  Maximum Value	2147483647
  Unit	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 ofgroup_replication_transaction_size_limit should be the same on all group members. For further mitigation strategies for large transactions, seeSection 17.3.2, “Group Replication Limitations”.

• group_replication_unreachable_majority_timeout

  Command-Line Format	--group-replication-unreachable-majority-timeout=#
  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
  Unit	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 usingSTOP GROUP REPLICATION on the members of the minority. Note thatgroup_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 theERROR state. 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.
  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 enter ERROR state.