LOGPOOL_FREEPOOLS

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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).

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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 770 in 2012 and 788 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. Waiting for access to the free pool manager (in this case while getting an empty buffer in the log pool to use to store a newly flushed log block)
2. Waiting for access to the free pool manager (in this case while making the log pool smaller as part of a log truncation from a checkpoint)

And other similar call stacks.

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

1. SOS_Task::PostWait+9e
   EventInternal<SuspendQueueSLock>::Wait+2ca
   SOS_RWLock::GetLongWait+10b
   SOS_RWLock::GetLock+122
   LogPoolSharedCacheBufferFreePoolMgr::WaitOnFreePool+47
   LogPoolSharedCacheBufferFreePoolMgr::Get+2c
   LogPoolSharedCacheBufferMgr::GetFreeBuffer+4b
   LogPoolSharedCacheBufferMgr::Push+112
   SQLServerLogMgr::FormatLC+110
   SQLServerLogMgr::FlushLC+50b
   SQLServerLogMgr::LogWriter+d62
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8
2. SOS_Task::PostWait+9e
   EventInternal<SuspendQueueSLock>::Wait+2ca
   SOS_RWLock::GetLongWait+10b
   LogPoolSharedCacheBufferFreePoolMgr::Put+160
   LogPoolSharedCacheBufferMgr::TruncateSharedCacheBufferPoolInt+108
   LogPoolSharedCacheBufferMgr::TruncateSharedCacheBufferPool+98
   LogPoolMgr::RightSizeCacheInternal+3d3
   LogPoolMgr::RightSizeCache+e0
   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