PAGELATCH_SH

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Description:

This wait type is when a thread is waiting for access to a data file page in memory so that it can read the page structure (SH = SHare mode). The Latches Whitepaper in the sidebar on the right has a description of all latch modes and their compatibility with other latch modes.

(Books Online description: “Occurs when a task is waiting on a latch for a buffer that is not in an I/O request. The latch request is in Shared mode.”)

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Added in SQL Server version:

Pre-2005/2005

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 50 in all versions through 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:

See the PAGELATCH_EX wait type for more details.

Note that you may see a wait resource of (0:0:0) in the output from some queries. This is normal – see this post for an explanation.

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

1. Reading a page in an index (in this case, while traversing from the root to the leaf level, searching for the insertion point of a new record)
2. Reading the allocation status of a page from a PFS page (in this case, while performing a scan of a heap)
3. Reading a page in an index (in this case, while finding a LOB value)

And many more similar stacks where pages in memory are being read.

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

1. SOS_Task::PostWait+90
   EventInternal::Wait+1f9
   LatchBase::Suspend+633
   LatchBase::AcquireInternal+415
   BUF::AcquireLatch+78
   BPool::Get+ea
   BTreeMgr::Seek+4a0
   BTreeMgr::GetHPageIdWithKey+32d
   IndexPageManager::GetPageWithKey+e6
   IndexDataSetSession::LocatePageForInsert+202
   IndexDataSetSession::InsertSmallRecord+dac
   IndexDataSetSession::SetDataInternal+99b8
   DatasetSession::SetData+16d
   RowsetNewSS::SetData+6a
   CValRow::SetDataX+63
   CQScanUpdateNew::GetRow+23a
   CQueryScan::GetRow+81
   CXStmtQuery::ErsqExecuteQuery+36a
   CXStmtDML::XretDMLExecute+2f3
   CXStmtDML::XretExecute+ad
   CMsqlExecContext::ExecuteStmts<1,1>+400
2. SOS_Task::PostWait+9e
   EventInternal::Wait+1fb
   LatchBase::Suspend+633
   LatchBase::AcquireInternal+415
   BUF::AcquireLatch+78
   BPool::Get+10f
   PFSPageRef::Fix+b2
   AllocScan::ProcessExtent+1a7
   AllocScan::GetNextScanExtent+500
   AllocScan::MoveToStartOfScan+192
   AllocScan::GetNextScanPage+18e
   AllocationOrderPageScanner::GetNextPage+a4
   HeapPageManager::GetNextPage+181
   HeapDataSetSession::GetNextRowValuesInternal+51f
   RowsetNewSS::FetchNextRow+197
   CQScanTableScanNew::GetRow+f2
   CQScanUpdateNew::GetRow+76
   CQueryScan::GetRow+81
   CXStmtQuery::ErsqExecuteQuery+36d
   CXStmtDML::XretDMLExecute+31c
   CXStmtDML::XretExecute+ad
   CMsqlExecContext::ExecuteStmts<1,1>+427
3. SOS_Task::PostWait+90
   EventInternal::Wait+1f9
   LatchBase::Suspend+633
   LatchBase::AcquireInternal+415
   BUF::AcquireLatch+78
   BPool::Get+ea
   BTreeMgr::Seek+4a0
   BTreeMgr::GetHPageIdWithKey+32d
   IndexPageManager::GetPageWithKey+e6
   GetRowForKeyValue+264
   IndexDataSetSession::GetRowByKeyValue+126
   IndexDataSetSession::FetchRowByKeyValueInternal+210
   DatasetSession::FetchRowByKeyValueNoLock+d0
   RowsetNewSS::FetchRowByKeyValue+4fd
   LobStorageProvider::GetLobValueForRead+74
   CBlobHandleFactoryMain::PilbGetILockBytesInternal+1a3
   CBlobHandleHelper::CopyBlobHandleIntoTempOrInlined+45
   CBlobHandleManagerCommon::PxvarPreprocessInternal+126
   CValExchangeLargeObject::SetDataX+88
   CQScanXProducerNew::CopyRow+a3
   CQScanXProducerNew::GetRowHelper+2e3