LOGPOOL_CACHESIZE

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Description:

This wait type is when a thread is waiting for an operation to do with the log pool. This is an in-memory cache of recently flushed log blocks, to help avoid log readers having to do physical reads of the log file (e.g. for sending log blocks to asynchronous availability group replicas).

(Books Online description: N/A)

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Added in SQL Server version:

2012

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 769 in 2012 and 787 in 2014 RTM. After 2014 RTM, you must check the DMV to get the latest value as some map_key values have changed in later builds.

Other information:

I have not seen this wait type be a noticeable contention point.

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

1. Changing the log pool cache size for a database (in this case, while performing a checkpoint as a database is going offline)
2. Changing the log pool cache size for a database (in this case, while performing a checkpoint for a database in the simple recovery mode, where the checkpoint has allowed some VLFs to be made inactive and they no longer need to take up space in the log pool)

And other similar call stacks.

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

1. SOS_Task::PostWait+9e
   EventInternal<SuspendQueueSLock>::Wait+1fb
   LogPoolMgr::RightSizeCache+af
   OfflineCheckpointWorker::GetNextLogBlock+cd
   OfflineCheckpointWorker::DoWorkInternal+f7
   OfflineCheckpointWorker::DoWork+3aa
   OfflineCheckpointWorker::WorkLoop+40f
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8
2. SOS_Task::PostWait+9e
   EventInternal<SuspendQueueSLock>::Wait+1fb
   LogPoolMgr::RightSizeCache+af
   LogTruncMgr::TruncateLog+14b
   IsSpaceFreedByCheckpoint+29c
   SafeCheckpoint+e0
   PerformLogTruncation+373
   ProcessLogTruncRequest+e6
   CheckpointHelper+1c2
   CheckpointLoopWorker+da
   RegisterCheckPtWorker+133
   CheckpointLoop+d3
   CheckpointThread+55
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8