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MySQL 8.0 Reference Manual  /  ...  /  Replication_group_member_stats

Pre-General Availability Draft: 2017-10-20

21.3.1 Replication_group_member_stats

Each member in a replication group certifies and applies transactions received by the group. Statistics regarding the certifier and applier procedures are useful to understand how the applier queue is growing, how many conflicts have been found, how many transactions were checked, which transactions are committed everywhere, and so on.

The performance_schema.replication_group_member_stats table provides group-level information related to the certification process, and also statistics for the transactions received and originated by each individual member of the replication group. 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. Note that refreshing of statistics for remote members is controlled by the message period specified in the group_replication_flow_control_period option, so these can differ slightly from the locally collected statistics for the member where the query is made.

Table 21.1 replication_group_member_stats

Field

Description

Channel_name

The name of the Group Replication channel.

View_id

The current view identifier for this group.

Member_id

The member server UUID. This has a different value for each member in the group. This also serves as a key because it is unique to each member.

Count_transactions_in_queue

The number of transactions in the queue pending conflict detection checks. Once the transactions have been checked for conflicts, if they pass the check, they are queued to be applied as well.

Count_transactions_checked

The number of transactions that have been checked for conflicts.

Count_conflicts_detected

The number of transactions that did not pass the conflict detection check.

Count_transactions_rows_validating

The current size of the conflict detection database (against which each transaction is certified).

Transactions_committed_all_members

The transactions that have been successfully committed on all members of the replication group. This is updated at a fixed time interval.

Last_conflict_free_transaction

The transaction identifier of the last conflict free transaction checked.

Count_transactions_remote_in_applier_queue

The number of transactions that this member has received from the replication group which are waiting to be applied.

Count_transactions_remote_applied

The number of transactions that this member has received from the replication group which have been applied.

Count_transactions_local_proposed

The number of transactions that this member originated and sent to the replication group for coordination.

Count_transactions_local_rollback

The number of transactions that this member originated that were rolled back after being sent to the replication group.


These fields are important for monitoring the performance of the members connected in the group. For example, suppose that one of the group’s members is delayed and is not able to keep up to date with the other members of the group. In this case you might see a large number of transactions in the queue. Based on this information, you could decide to either remove the member from the group, or delay the processing of transactions on the other members of the group in order to reduce the number of queued transactions. This information can also help you to decide how to adjust the flow control of the Group Replication plugin.


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