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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