18.4.2 Group Replication Server States

There are various states that a server instance can be in. If servers are communicating properly, all report the same states for all servers. However, if there is a network partition, or a server leaves the group, then different information could be reported, depending on which server is queried. If the server has left the group then it cannot report updated information about the other servers' states. If there is a partition, such that quorum is lost, servers are not able to coordinate between themselves. As a consequence, they cannot guess what the status of different servers is. Therefore, instead of guessing their state they report that some servers are unreachable.

Table 18.1 Server State

Field

Description

Group Synchronized

ONLINE

The member is ready to serve as a fully functional group member, meaning that the client can connect and start executing transactions.

Yes

RECOVERING

The member is in the process of becoming an active member of the group and is currently going through the recovery process, receiving state transfer from a donor.

No

OFFLINE

The Group Replication plugin is loaded but the member does not belong to any group.

No

ERROR

The member is in an error state and is not functioning correctly as a group member. Depending on the exit action set by group_replication_exit_state_action, the member is in read-only mode (super_read_only=ON) and could also be in offline mode (offline_mode=ON). Note that a server in offline mode following the OFFLINE_MODE exit action is displayed with ERROR status, not OFFLINE. A server with the exit action ABORT_SERVER shuts down and is removed from the view of the group.

No

UNREACHABLE

Whenever the local failure detector suspects that a given server is not reachable, because for example it was disconnected involuntarily, it shows that server's state as UNREACHABLE.

No