PAGELATCH_UP

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Description:

This wait type is when a thread is waiting for access to a data file page in memory (usually an allocation bitmap page) so that it can update the page structure (UP = UPdate 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 Update 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 51 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.

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

1. Setting the ‘this page is allocated’ bit in the byte for a page in a PFS page (in this case, while allocating the page that an index page will split into during a page split from an insert)
2. Setting the ‘this page has one or more ghost records’ bit in the byte for a page in a PFS page (in this case, as part of deleting a row from a nonclustered index on the sys.sysrowsets Storage Engine system table while dropping a rowset as part of a DROP TABLE)
3. Clearing the ‘this page is allocated’ bit in the byte for a page in a PFS page (in this case, while doing a background deferred drop of a large allocation unit)
4. Setting the ‘this extent is allocated’ bit for an extent in an IAM page (in this case, while allocating a page that will be the target of a page move during a data file shrink)
5. Setting the ‘this extent has changed’ bit for an extent in a differential bitmap page (in this case, while allocating a page to store statistics being created by an UPDATE STATISTICS)

And many more similar stacks where allocation bitmap pages in memory are being updated.

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

1. SOS_Task::PostWait+9e
   EventInternal::Wait+1fb
   LatchBase::Suspend+633
   LatchBase::AcquireInternal+415
   TargetExtentMgr::AllocPageFromTargetExtent+5d3
   AllocationReq::AllocateFromExistingExtents+9e1
   AllocationReq::AllocatePages+15ba
   AllocationReq::Allocate+f3
   AllocateHoBtDataPage+5fd
   IndexPageManager::AllocatePage+1b8
   SplitPage+b48
   IndexDataSetSession::InsertSmallRecord+1a1d
   IndexDataSetSession::InsertRowInternal+2de1
   DatasetSession::InsertRow+163
   RowsetNewSS::InsertRow+26
   CValRow::SetDataX+5b
   sqlTsEs.dll!0x000007FEF1C31437
   CQScanScalarInsertNew::GetRow+94
   CQueryScan::GetRow+81
   CXStmtQuery::ErsqExecuteQuery+36d
   CXStmtDML::XretDMLExecute+31c
   CXStmtDML::XretExecute+ad
2. SOS_Task::PostWait+9e
   EventInternal::Wait+1fb
   LatchBase::Suspend+633
   LatchBase::AcquireInternal+415
   BUF::AcquireLatch+78
   BPool::Get+10f
   PFSPageRef::Fix+b2
   ChangeGhostPageState+e0
   IndexPageRef::MarkGhost+1366
   BTreeRow::DeleteRecord+1782
   IndexDataSetSession::DeleteRow+296
   RowsetNewSS::DeleteRows+4e
   CMEDScan::DeleteNCRow+27a
   CMEDScan::DeleteRow+4b
   CMEDCatKatmaiIndex::DropRowset+55c
   VisibleHoBt::DropHoBt+35d
   SEDropRowsetInternal+79c
   DDLAgent::SEDropRowsets+4b
   CIndexDDL::DropRowset+c0
   DropAllRowsetsForTable+173
   DropObject+126
3. SOS_Task::PostWait+9e
   EventInternal::Wait+1fb
   LatchBase::Suspend+633
   LatchBase::AcquireInternal+415
   BUF::AcquireLatch+78
   BPool::Get+10f
   PFSPageRef::Fix+b2
   DeAllocateMixedPage+4ce
   DeferredAllocUnitDrop::DeAllocateDataPagesInIAM+29a
   DeferredAllocUnitDrop::DeAllocateFirstIAMAndItsExtents+1ea
   DeferredAllocUnitDrop::ProcessOneIAM+91
   DeferredAllocUnitDrop::Process+1a3
   DeferredAllocUnitDrop::AllocUnitCleanupTask+76
   PeriodicTimerTask::ProcessTskPkt+a
   TaskReqPktTimer::ExecuteTask+63
   OnDemandTaskContext::ProcessTskPkt+3e2
   SystemTaskEntryPoint+426
   OnDemandTaskContext::FuncEntryPoint+25
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+ab
4. SOS_Task::PostWait+9e
   EventInternal::Wait+1fb
   LatchBase::Suspend+633
   LatchBase::AcquireInternal+415
   ChangeExtStateInIAM+2f3
   AllocationReq::AllocatePages+1ee4
   AllocationReq::Allocate+f3
   AllocateHoBtDataPage+5fd
   IndexPageManager::AllocatePage+1b8
   IndexPageManager::SwapPage+f8
   SwapPageUnderSystemTransaction+442
   IndexDataSetSession::MoveDataPageCommon+91f
   IndexDataSetSession::MovePages+2c0
   IndexDataSetSession::ShrinkInternal+f7
   DatasetSession::Shrink+b2
   UtilDbccMoveBtreePages+2ca
   UtilDbccMovePages+1cbd
   UtilDbccProcessPagesInShrink+62d
   UtilDbccShrinkDataFiles+18c8
   UtilDbccShrinkDataFiles+76e
   UtilDbccShrinkDatabase+8fc
   DbccShrink+49e
5. SOS_Task::PostWait+9e
   EventInternal::Wait+1fb
   LatchBase::Suspend+633
   LatchBase::AcquireInternal+415
   BUF::AcquireLatch+78
   PageRef::SetDiffMapChangeBit+11a
   PageRef::FormatInternal+125
   AllocateHoBtDataPage+8c4
   IndexPageManager::AllocatePage+1b8
   SplitPage+b48
   BTreeRow::UpdateRecord+1f41
   IndexDataSetSession::SetDataInternal+9a03
   DatasetSession::SetData+16d
   RowsetNewSS::SetData+6a
   CMEDScanBase::FUpdateSingleRow+be
   CMEDScan::FUpdateRow+5ae
   CMEDCatYukonObject::SetStatsBlob+47a
   CMEDProxyStats::SetBlob+236
   CStatMan::PersistBlob+1bf
   CStatMan::PersistBlob+50
   CStatsUtil::PersistQPStatsInCatalogs+87f
   CStatsUtil::FUpdateQPStatsHelper+f7e