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How to Analyze "Deadlocked Schedulers" Dumps?

How to Analyze "Deadlocked Schedulers" Dumps?

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How to Analyze "Deadlocked Schedulers" Dumps?

Newer version of this post is available in http://mssqlwiki.com/2010/06/15/how-to-analyze-deadlocked-schedulers-dumps/

Do you see "Deadlocked Schedulers" errors similar to one below and
stuck?

From SQLServer Errorlog

**Dump thread - spid = 0, PSS = 0x0000000000000000, EC =
0x0000000000000000

***Stack Dump being sent to C:\Program Files\Microsoft SQL
Server\MSSQL.1\MSSQL\LOG\SQLDump0001.txt

* BEGIN STACK DUMP:

* Deadlocked Schedulers

* Short Stack Dump

Stack Signature for the dump is 0x00000000000003D0

New queries assigned to process on Node 0 have not been picked  up by a worker thread in the last 60 seconds. Blocking or long-running queries can
contribute to this condition, and may degrade client response time.  Use the "max worker threads" configuration option to increase number  of allowable
threads, or optimize current running queries.  SQL Process Utilization: 0%. System Idle: 69%.

Cause

We get Deadlocked Schedulers error when Scheduler Monitor detects Threads(workers) are not Progressing on schedulers.

Some of common causes are

1.Most of the tasks are waiting on a single resource and SQL Server could not spawn new thread to take new work request and there is no Idle thread to process the new work Request . In systems with multiple nodes (Numa)  If all the threads which belong to schedulers of single node is exhausted (or)  Schedulers not progressing on single node can cause deadlocked scheduler condition.

2.   Excessive blocking, Very long running Queries executed by all workers, All the threads waiting on some resource.

 

 

Steps to analyze "Deadlocked Schedulers" Dumps.

To analyze the dump download and Install Windows Debugger from This  link

Step 1:

Open Windbg .  Choose File menu –> select Open crash dump –>Select the Dump file (SQLDump000#.mdmp)

Step 2:

on command window type
.sympath srv*c:\Websymbols*http://msdl.microsoft.com/download/symbols;

Step 3:

Type .reload /f and hit enter. This will force debugger to immediately load all the symbols.

Step 4:

Verify if symbols are loaded for  SQL Server by using the debugger command lmvm

0:002> lmvm sqlservr
start             end                 module name
00000000`01000000 00000000`03679000   sqlservr T (pdb symbols)          c:\websymbols\sqlservr.pdb\21E4AC6E96294A529C9D99826B5A7C032\sqlservr.pdb
    Loaded symbol image file: sqlservr.exe
    Image path: C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Binn\sqlservr.exe
    Image name: sqlservr.exe
    Timestamp:        Wed Oct 07 21:15:52 2009 (4ACD6778)
    CheckSum:         025FEB5E
    ImageSize:        02679000
    File version:     2005.90.4266.0
    Product version:  9.0.4266.0
    File flags:       0 (Mask 3F)
    File OS:          40000 NT Base
    File type:        1.0 App
    File date:        00000000.00000000
    Translations:     0000.04b0 0000.04e4 0409.04b0 0409.04e4

Step 5:

Type  ~*kL 20   and look at the stack of all the threads  to find what majority of threads are doing.

1. If it is blocking issue and If most of the threads are  waiting to
acquire a lock you will find the most of the stack similar to one below. (We try
to acquire lock and go to wait, since someone is holding a lock)

ntdll!ZwSignalAndWaitForSingleObject

kernel32!SignalObjectAndWait

sqlservr!SOS_Scheduler::SwitchContext

sqlservr!SOS_Scheduler::Suspend

sqlservr!SOS_Event::Wait

sqlservr!LockOwner::Sleep

sqlservr!lck_lockInternal

sqlservr!GetLock

2. If most of threads are stuck while trying to write profiler events
to the destination you might find stack similar to one below

ntdll!ZwSignalAndWaitForSingleObject

kernel32!SignalObjectAndWait

sqlservr!SOS_Scheduler::SwitchContext

sqlservr!SOS_Task::Sleep

sqlservr!CTraceRowsetIoProvider::GetFreeBuffers

sqlservr!CTraceWriteRequest::InitForRowsetTrace

sqlservr!CTraceRowsetIoProvider::InitializeWriteRequest

sqlservr!CTrace::WriteRecord

sqlservr!CTraceController::ProduceRecord

sqlservr!CTraceData::TracePreBatchEvent

sqlservr!CSQLSource::Execute

sqlservr!process_request

sqlservr!process_commands

sqlservr!SOS_Task::Param::Execute

sqlservr!SOS_Scheduler::RunTask

sqlservr!SOS_Scheduler::ProcessTasks

3. If your stack’s  are like one below refer http://support.microsoft.com/default.aspx?scid=kb;EN-US;974205

sqlservr!SpinlockBase::Sleep sqlservr!SpinlockBase::SpinToAcquire 
sqlservr!TSyncHashTable_EntryAccessorsqlservr!CQSIndexStatsMgr::AddNewMissingIndex 
sqlservr!CIdxSuggestion::Register 
sqlservr!COptExpr::PqteConvert sqlservr!CPhyOp_Top::PqteConvert sqlservr!COptExpr::PqteConvert 
sqlservr!COptExpr::PqteConvertTree sqlservr!COptContext::PcxteOptimizeQuery 
sqlservr!CQuery::Optimize sqlservr!CQuery::PqoBuild sqlservr!CStmtQuery::InitQuery 
sqlservr!CStmtSelect::Init
 

4. If you see many stacks like the one below it could be BPOOL memory
pressure (or) Lazy writer  waiting on I/O

sqlservr!BPool::Steal

sqlservr!SQLSinglePageAllocator::AllocatePages

sqlservr!MemoryNode::AllocatePagesInternal

sqlservr!MemoryClerkInternal::AllocatePages

sqlservr!IMemObj::PbGetNewPages

sqlservr!CSlotPageMgr::PbAllocate

 

5. If you see many stacks like the one below it should be because of
excessive parallelism

sqlservr!CQScanXProducerNew::Open

sqlservr!FnProducerOpen

sqlservr!FnProducerThread

sqlservr!SubprocEntrypoint

 

6. If you see many stacks like the one below (Many threads waiting to
flush log) it should be because of disk bottleneck's. Check if you see "I/O
requests taking longer than 15 seconds" messages in Errorlog before Deadlocked
Schedulers Dumps. Refer http://mssqlwiki.com/sqlwiki/sql-performance/io-bottlenecks/
for troubleshooting I/O issues.

sqlservr!SOS_Event::Wait
sqlservr!SQLServerLogMgr::WaitLCFlush

sqlservr!SQLServerLogMgr::LogFlush

sqlservr!SQLServerLogMgr::WaitLogFlush


sqlservr!XdesRMFull::Commit

 

 

Related blogs:

http://mssqlwiki.com/sqlwiki/sql-performance/basics-of-sql-server-memory-architecture/

http://mssqlwiki.com/sqlwiki/sql-performance/windows-2008-and-windows-2008-r2-known-issues-related-to-working-set-memory/

http://mssqlwiki.com/2012/05/18/sql-server-performance-degraded-in-32-bit-sql-server-after-i-adding-additional-ram/

http://mssqlwiki.com/sqlwiki/sql-performance/troubleshooting-sql-server-memory/

http://mssqlwiki.com/sqlwiki/sql-performance/io-bottlenecks/

 

If you liked this post, do like us on FaceBook at https://www.facebook.com/mssqlwiki and join our FaceBook group https://www.facebook.com/mssqlwiki#!/groups/454762937884205/

 

Regards

Karthick P.K

Comments
  • Thanks for sharing this article.

  • I'm trying to review one of our dumps but do not get the nice names for the sqlservr! entries. I am not loading the SQL symbols?

    Thanks for this post.

  • Contain very good information. Thans You Karthick

  • Good article

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