Replica SQL Thread States

This article documents thread states that are related to replication slave SQL threads. These correspond to the Slave_SQL_State shown by SHOW SLAVE STATUS as well as the STATE values listed by the SHOW PROCESSLIST statement and the Information Schema PROCESSLIST as well as the PROCESSLIST_STATE value listed in the Performance Schema threads Table.

Value	Description
Value	Description
Apply log event	Log event is being applied.
Making temp file	Creating a temporary file containing the row data as part of a LOAD DATA INFILE statement.
Reading event from the relay log	Reading an event from the relay log in order to process the event.
Slave has read all relay log; waiting for the slave I/O thread to update it	All relay log events have been processed, now waiting for the I/O thread to write new events to the relay log.
Waiting for work from SQL thread	In parallel replication the worker thread is waiting for more things from the SQL thread.
Waiting for prior transaction to start commit before starting next transaction	In parallel replication the worker thread is waiting for conflicting things to end before starting executing.
Waiting for worker threads to be idle	Happens in parallel replication when moving to a new binary log after a master restart. All slave temporary files are deleted and worker threads are restarted.
Waiting due to global read lock	In parallel replication when worker threads are waiting for a global read lock to be released.
Waiting for worker threads to pause for global read lock	FLUSH TABLES WITH READ LOCK is waiting for worker threads to finish what they are doing.
Waiting while replication worker thread pool is busy	Happens in parallel replication during a FLUSH TABLES WITH READ LOCK or when changing number of parallel workers.
Waiting for other master connection to process GTID received on multiple master connections	A worker thread noticed that there is already another thread executing the same GTID from another connection and it's waiting for the other to complete.
Waiting for slave mutex on exit	Thread is stopping. Only occurs very briefly.
Waiting for the next event in relay log	State before reading next event from the relay log.

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