PARALLEL_REDO_WORKER_SYNC

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Description:

This wait type is when the main parallel redo thread in an Availability Group replica is waiting for the redo worker threads to complete. This wait is part of normal parallel redo operations.

(Books Online description: N/A)

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Added in SQL Server version:

2016

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 1131 in 2016 RTM. After 2016 RTM, you must check the DMV to get the latest value as some map_key values have changed in later builds.

Other information:

This wait type is one that I usually filter out as a benign wait when doing wait statistics analysis as it is documented as not being indicative of a performance issue.

You can read more about parallel redo in this blog post.

Known occurrences in SQL Server (list number matches call stack list):

1. Waiting for parallel redo work threads to complete (in this case, while running recovery as part of CREATE DATABASE operation)
2. Waiting for parallel redo work threads to complete (in this case, while running recovery as part of RESTORE DATABASE operation)

And other similar call stacks.

Abbreviated call stacks (list number matches known occurrences list):

1. SOS_Task::PostWait+0x6f
   EventInternal<SuspendQueueSLock>::Wait+0x1f4
   ParallelRedoManager::StopRedoWorkers+0x115
   RecoveryMgr::Cleanup+0xc0
   RecoveryUnit::DoRollbackRecovery+0x49
   RecoveryUnit::CompleteRecovery+0x6ef
   DBTABLE::StartupPostRecovery+0x9f
   DBTABLE::Startup+0x1475
   DBMgr::StartupDB+0x7d5
   CStmtCreateDB::CreateLocalDatabaseFragment+0x99d
   DBDDLAgent::CreateDatabase+0x12b
   CStmtCreateDB::XretExecute+0x1253
   CMsqlExecContext::ExecuteStmts<1,1>+0x40d
   CMsqlExecContext::FExecute+0xa9e
   CSQLSource::Execute+0x981
   process_request+0xe61
   process_commands_internal+0x2df
   process_messages+0x253
   SOS_Task::Param::Execute+0x231
   SOS_Scheduler::RunTask+0xaa
2. SOS_Task::PostWait+0x6f
   EventInternal<SuspendQueueSLock>::Wait+0x1f4
   ParallelRedoManager::StopRedoWorkers+0x115
   RecoveryMgr::Cleanup+0xc0
   RecoveryUnit::DoRollbackRecovery+0x49
   RecoveryUnit::CompleteRecovery+0x6ef
   DBTABLE::StartupPostRecovery+0x9f
   DBTABLE::Startup+0x1475
   DBMgr::StartupDB+0x7d5
   BackupOperation::StartupDb+0x1e3
   BackupOperation::StartDatabaseForOnline+0x222
   BackupOperation::BringDatabaseFullyOnline+0x4ce
   BackupOperation::CompleteRestore+0x432
   BackupOperation::Restore+0xeea
   BackupEntry::RestoreDatabase+0x304
   CStmtLoadDb::XretExecute+0x10f
   CMsqlExecContext::ExecuteStmts<1,1>+0x40d
   CMsqlExecContext::FExecute+0xa9e
   CSQLSource::Execute+0x981
   process_request+0xe61