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Description:
This wait type is a generic wait for when a thread is calling one of several Windows functions related to finding files.
(Books Online description: N/A)
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Added in SQL Server version:
2008
Removed in SQL Server version:
N/A
Extended Events wait_type value:
The map_key value in sys.dm_xe_map_values is 449 in 2008 and 2008 R2, 497 in 2012, and 513 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.
Note that when a thread calls out to Windows, the thread changes from non-preemptive (SQL Server controls the thread) to preemptive (Windows controls the thread) mode. The thread’s state will be listed as RUNNING, as SQL Server doesn’t know what Windows is doing with the thread.
Known occurrences in SQL Server (list number matches call stack list):
- Finding a file (in this case, while running the FILESTREAM consistency-checking portion of the allocation checks in DBCC CHECKDB)
- Finding a file (in this case, while running the FILESTREAM consistency-checking portion of the logical checks in DBCC CHECKDB)
- finding a file (in this case, while truncating the FILESTREAM ‘log’ as part of running a checkpoint operation)
And other similar call stacks.
Abbreviated call stacks (list number matches known occurrences list):
- SOS_Task::PopWait+b1
AutoSwitchPreemptive::~AutoSwitchPreemptive+95
FsLogIter::MoveNext+2db
STREAMFCB::FindNextDeletedRowset+27f
StreamFileMgr::DbccCheckForRowsetDirs+1a6
CheckAllocations::ExtractRowsetDirFactsFromFSManager+8b
CheckAllocations::ExtractFactsFromSEMetadata+142b
CheckAllocations::ProcessNextData+1fe
CheckAggregateSingleInstance::GetNextFact+28e
CTRowsetInstance::FGetNextRow+3c
CUtRowset::GetNextRows+a0
CQScanRmtScanNew::GetRowHelper+3b5
CQScanSortNew::BuildSortTable+246
CQScanSortNew::OpenHelper+c0
CQScanNew::OpenHelper+41
CQScanStreamAggregateNew::Open+30
CQueryScan::StartupQuery+23c
CXStmtQuery::SetupQueryScanAndExpression+2e5
CXStmtQuery::InitForExecute+34
CXStmtQuery::ErsqExecuteQuery+36d
CXStmtSelect::XretExecute+2e7
CMsqlExecContext::ExecuteStmts<1,1>+427 - SOS_Task::PopWait+b1
AutoSwitchPreemptive::~AutoSwitchPreemptive+95
TreeScan::FetchNext+3d8
CFsFileRowset::FindNextFileW+10a
CFsRowset::FindNextFileW+76
CheckTables::CollectFSFileFactsFromFSManager+51a
CheckTables::ProcessPage+588
CheckTables::ProcessNextData+34f
CheckAggregateSingleInstance::GetNextFact+28e
CTRowsetInstance::FGetNextRow+3c
CUtRowset::GetNextRows+a0
CQScanRmtScanNew::GetRowHelper+3b5
CQScanSortNew::BuildSortTable+246
CQScanSortNew::OpenHelper+c0
CQScanNew::OpenHelper+41
CQScanStreamAggregateNew::Open+30
CQueryScan::StartupQuery+23c
CXStmtQuery::SetupQueryScanAndExpression+2e5
CXStmtQuery::InitForExecute+34
CXStmtQuery::ErsqExecuteQuery+36d
CXStmtSelect::XretExecute+2e7
CMsqlExecContext::ExecuteStmts<1,1>+427 - SOS_Task::PopWait+b1
AutoSwitchPreemptive::~AutoSwitchPreemptive+95
FsLogIter::MoveNext+f7
STREAMFCB::TruncatepH6FsLog+15c
FsLogTruncMgr::TruncateLog+261
FsLogTruncMgr::ProcessFsLogTruncationForDB+116
RecoveryUnit::ProcessCheckpointEnd+6af
HardenAndLogCheckpoint+e3d
CheckpointRU2+278
AsynchronousDiskAction::DoFlushCache+98
AsynchronousDiskAction::ExecuteDeferredAction+246
AsynchronousDiskPool::PerformActionsSerially+61
AsynchronousDiskPool::WaitUntilDoneOrTimeout+71
CheckpointDB2+2eb
CheckpointWithOptionalTruncate+c5
DBOpAgent::CheckpointDBHandler+1e
CStmtCheckpoint::XretExecute+e7
CMsqlExecContext::ExecuteStmts<1,1>+427
CMsqlExecContext::FExecute+a43
CSQLSource::Execute+86c