29.12.11.8 The replication_applier_status_by_worker Table

This table provides details of the transactions handled by applier threads on a replica or Group Replication group member. For a single-threaded replica, data is shown for the replica's single applier thread. For a multithreaded replica, data is shown individually for each applier thread. The applier threads on a multithreaded replica are sometimes called workers. The number of applier threads on a replica or Group Replication group member is set by the replica_parallel_workers or slave_parallel_workers system variable, which is set to zero for a single-threaded replica. A multithreaded replica also has a coordinator thread to manage the applier threads, and the status of this thread is shown in the replication_applier_status_by_coordinator table.

All error codes and messages displayed in the columns relating to errors correspond to error values listed in Server Error Message Reference.

When the Performance Schema is disabled, local timing information is not collected, so the fields showing the start and end timestamps for applied transactions are zero. The start timestamps in this table refer to when the worker started applying the first event, and the end timestamps refer to when the last event of the transaction was applied.

When a replica is restarted by a START REPLICA statement, the columns beginning APPLYING_TRANSACTION are reset. Before MySQL 8.0.13, these columns were not reset on a replica that was operating in single-threaded mode, only on a multithreaded replica.

The replication_applier_status_by_worker table has these columns:

• CHANNEL_NAME

  The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 19.2.2, “Replication Channels” for more information.

• WORKER_ID

  The worker identifier (same value as the id column in the mysql.slave_worker_info table). After STOP REPLICA, the THREAD_ID column becomes NULL, but the WORKER_ID value is preserved.

• THREAD_ID

  The worker thread ID.

• SERVICE_STATE

  ON (thread exists and is active or idle) or OFF (thread no longer exists).

• LAST_ERROR_NUMBER, LAST_ERROR_MESSAGE

  The error number and error message of the most recent error that caused the worker thread to stop. An error number of 0 and message of the empty string mean “no error”. If the LAST_ERROR_MESSAGE value is not empty, the error values also appear in the replica's error log.

  Issuing RESET MASTER or RESET REPLICA resets the values shown in these columns.

• LAST_ERROR_TIMESTAMP

  A timestamp in 'YYYY-MM-DD hh:mm:ss[.fraction]' format that shows when the most recent worker error occurred.

• LAST_APPLIED_TRANSACTION

  The global transaction ID (GTID) of the last transaction applied by this worker.

• LAST_APPLIED_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP

  A timestamp in 'YYYY-MM-DD hh:mm:ss[.fraction]' format that shows when the last transaction applied by this worker was committed on the original source.

• LAST_APPLIED_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP

  A timestamp in 'YYYY-MM-DD hh:mm:ss[.fraction]' format that shows when the last transaction applied by this worker was committed on the immediate source.

• LAST_APPLIED_TRANSACTION_START_APPLY_TIMESTAMP

  A timestamp in 'YYYY-MM-DD hh:mm:ss[.fraction]' format that shows when this worker started applying the last applied transaction.

• LAST_APPLIED_TRANSACTION_END_APPLY_TIMESTAMP

  A timestamp in 'YYYY-MM-DD hh:mm:ss[.fraction]' format that shows when this worker finished applying the last applied transaction.

• APPLYING_TRANSACTION

  The global transaction ID (GTID) of the transaction this worker is currently applying.

• APPLYING_TRANSACTION_ORIGINAL_COMMIT_TIMESTAMP

  A timestamp in 'YYYY-MM-DD hh:mm:ss[.fraction]' format that shows when the transaction this worker is currently applying was committed on the original source.

• APPLYING_TRANSACTION_IMMEDIATE_COMMIT_TIMESTAMP

  A timestamp in 'YYYY-MM-DD hh:mm:ss[.fraction]' format that shows when the transaction this worker is currently applying was committed on the immediate source.

• APPLYING_TRANSACTION_START_APPLY_TIMESTAMP

  A timestamp in 'YYYY-MM-DD hh:mm:ss[.fraction]' format that shows when this worker started its first attempt to apply the transaction that is currently being applied. Before MySQL 8.0.13, this timestamp was refreshed when a transaction was retried due to a transient error, so it showed the timestamp for the most recent attempt to apply the transaction.

• LAST_APPLIED_TRANSACTION_RETRIES_COUNT

  The number of times the last applied transaction was retried by the worker after the first attempt. If the transaction was applied at the first attempt, this number is zero.

• LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_NUMBER

  The error number of the last transient error that caused the transaction to be retried.

• LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_MESSAGE

  The message text for the last transient error that caused the transaction to be retried.

• LAST_APPLIED_TRANSACTION_LAST_TRANSIENT_ERROR_TIMESTAMP

  A timestamp in 'YYYY-MM-DD hh:mm:ss[.fraction]' format for the last transient error that caused the transaction to be retried.

• APPLYING_TRANSACTION_RETRIES_COUNT

  The number of times the transaction that is currently being applied was retried until this moment. If the transaction was applied at the first attempt, this number is zero.

• APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_NUMBER

  The error number of the last transient error that caused the current transaction to be retried.

• APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_MESSAGE

  The message text for the last transient error that caused the current transaction to be retried.

• APPLYING_TRANSACTION_LAST_TRANSIENT_ERROR_TIMESTAMP

  A timestamp in 'YYYY-MM-DD hh:mm:ss[.fraction]' format for the last transient error that caused the current transaction to be retried.

The replication_applier_status_by_worker table has these indexes:

• Primary key on (CHANNEL_NAME, WORKER_ID)

• Index on (THREAD_ID)

The following table shows the correspondence between replication_applier_status_by_worker columns and SHOW REPLICA STATUS columns.

replication_applier_status_by_worker Column	SHOW REPLICA STATUS Column
WORKER_ID	None
THREAD_ID	None
SERVICE_STATE	None
LAST_ERROR_NUMBER	Last_SQL_Errno
LAST_ERROR_MESSAGE	Last_SQL_Error
LAST_ERROR_TIMESTAMP	Last_SQL_Error_Timestamp