The
performance_schema.replication_group_members
table is used for monitoring the status of the different server
instances that are members of the group. The information in the
table is updated whenever there is a view change, for example when
the configuration of the group is dynamically changed when a new
member joins. At that point, servers exchange some of their
metadata to synchronize themselves and continue to cooperate
together. The information is shared between all the server
instances that are members of the replication group, so
information on all the group members can be queried from any
member. This table can be used to get a high level view of the
state of a replication group, for example by issuing:
SELECT * FROM performance_schema.replication_group_members;
+---------------------------+--------------------------------------+-------------+-------------+--------------+-------------+----------------+----------------------------+
| CHANNEL_NAME | MEMBER_ID | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE | MEMBER_ROLE | MEMBER_VERSION | MEMBER_COMMUNICATION_STACK |
+---------------------------+--------------------------------------+-------------+-------------+--------------+-------------+----------------+----------------------------+
| group_replication_applier | d391e9ee-2691-11ec-bf61-00059a3c7a00 | example1 | 4410 | ONLINE | PRIMARY | 8.4.3 | XCom |
| group_replication_applier | e059ce5c-2691-11ec-8632-00059a3c7a00 | example2 | 4420 | ONLINE | SECONDARY | 8.4.3 | XCom |
| group_replication_applier | ecd9ad06-2691-11ec-91c7-00059a3c7a00 | example3 | 4430 | ONLINE | SECONDARY | 8.4.3 | XCom |
+---------------------------+--------------------------------------+-------------+-------------+--------------+-------------+----------------+----------------------------+
3 rows in set (0.0007 sec)
Based on this result we can see that the group consists of three
members. Shown in the table is each member's
server_uuid
, as well as the
member's host name and port number, which clients use to connect
to it. The MEMBER_STATE
column shows one of the
Section 20.4.2, “Group Replication Server States”, in this case it
shows that all three members in this group are
ONLINE
, and the MEMBER_ROLE
column shows that there are two secondaries, and a single primary.
Therefore this group must be running in single-primary mode. The
MEMBER_VERSION
column can be useful when you
are upgrading a group and are combining members running different
MySQL versions. The MEMBER_COMMUNICATION_STACK
column shows the communication stack used for the group.
For more information about the MEMBER_HOST
value and its impact on the distributed recovery process, see
Section 20.2.1.3, “User Credentials For Distributed Recovery”.