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How do I find what queries were executing in a SQL memory dump?

  • Artikkeli

NOTE: This post has been updated in a new post due to an issue found with the steps in this post. The procedure is the same, but the steps here may only work with 32 bit dumps. Please read the post located at the address below:

https://blogs.msdn.com/b/askjay/archive/2011/02/18/finding-which-queries-were-executing-from-a-sql-memory-dump-revisited.aspx

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In this post, we’ll see how to find out which queries were executing from a SQL Server memory dump. You might have a dump file from a crash of the SQL Service, or you may have taken a diagnostic dump with sqldumper.

What we do in this post assumes you are working with a full or filtered dump of SQL Server. For more information on dumping SQL Server, read this post:

https://blogs.msdn.com/b/askjay/archive/2010/02/05/how-can-i-create-a-dump-of-sql-server.aspx

Some of the objects contained in the dump that are needed to completely understand this process can only be resolved with private symbols. What this means is that to fully track down the executing query text, you need to be internal to MS with access to “private” symbols.

However, after finding the query text with the private symbols, we can quickly get to the query text with public symbols and a few specific memory addresses and offsets.

So first, set your public symbol path:

0:000> .sympath srv*c:\symbols\public*https://msdl.microsoft.com/download/symbols
Symbol search path is: srv*c:\symbols\public*https://msdl.microsoft.com/download/symbols
0:000> .reload /f sqlservr.exe

Search the stacks:

0:000> ~* k

You are looking for a stack that is executing a query. It will look like this:

 

Call Site
ntdll!ZwWaitForSingleObject+0xa
KERNELBASE!WaitForSingleObjectEx+0x9c
sqlservr!SOS_Scheduler::Switch+0xc7
sqlservr!ThreadScheduler::SwitchNonPreemptive+0xc6
sqlservr!AutoSwitchPreemptive::~AutoSwitchPreemptive+0x39
sqlservr!SOS_Task::AutoSwitchPreemptive::~AutoSwitchPreemptive+0x26
sqlservr!Np::StatusWriteNoComplPort+0xc3
sqlservr!SNIStatusWriteNoComplPort+0x59
sqlservr!TDSSNIClient::WriteStatus+0x99
sqlservr!write_data+0x1bf
sqlservr!flush_buffer+0xf3
sqlservr!CKatmaiTds::SendRowImpl+0x19c
sqlservr!CEs::GeneralEval+0x91f
sqlservr!CXStmtQuery::ErsqExecuteQuery+0xe3a

sqlservr!CMsqlExecContext::ExecuteStmts<1,1>+0xb6c sqlservr!CMsqlExecContext::FExecute+0x593
sqlservr!CSQLSource::Execute+0x2f9 sqlservr!process_request+0x370
sqlservr!process_commands+0x2b2
sqlservr!SOS_Task::Param::Execute+0x11b
sqlservr!SOS_Scheduler::RunTask+0xca
sqlservr!SOS_Scheduler::ProcessTasks+0x95
sqlservr!SchedulerManager::WorkerEntryPoint+0x110
sqlservr!SystemThread::RunWorker+0x60
sqlservr!SystemThreadDispatcher::ProcessWorker+0x12c
sqlservr!SchedulerManager::ThreadEntryPoint+0x12f
msvcr80!_callthreadstartex+0x17 [f:\dd\vctools\crt_bld\self_64_amd64\crt\src\threadex.c @ 348]
msvcr80!_threadstartex+0x84 [f:\dd\vctools\crt_bld\self_64_amd64\crt\src\threadex.c @ 326]
kernel32!BaseThreadInitThunk+0xd
ntdll!RtlUserThreadStart+0x21

We are interested in the 3rd parameter of the sqlservr!CMsqlExecContext::ExecuteStmts call as seen below:

0e 00000000`0f6eee80 00000000`00e90fe3 : 00000064`00000000
00000001`00000000
00000000`86909380
00000000`00000000
: sqlservr!CMsqlExecContext::ExecuteStmts<1,1>+0xb6c

This is the address of an object, and we need to dump 1 dword at an offset of 0x20 into this object:

0:041> dd 86909380+0x020 l1
00000000`869093a0 869093e0

The address at this offset into the object is a property that contains a pointer (another address) to the buffer that contains our query text. So we get our address from here:

0:041> dd 869093e0 l1
00000000`869093e0 86909470

Now this is the address we need. So we dump unicode string on this address and we get our query:

0:041> du 86909470
00000000`86909470 "....select * from Sales.SalesOrd"
00000000`869094b0 "erHeaderroductLevel');..a"

You should be able to follow this approach for most threads executing queries. The signature of the “ExecuteStmts” function (a method of the CMsqlExecContext object) should have the object address we need as the 3rd parameter provided the stack is the same (the method could be overloaded and take something else as the 3rd parameter in a different situation – but I’d have to check).

-Jay

Comments

  • Anonymous
    October 23, 2010
    0e 000000000f6eee80 0000000000e90fe3 : 0000006400000000000000010000000000000000869093800000000000000000Can you tell me how do you get this information?When I use the k command ,I only get something like this：3f20f8f8 01540cc0 sqlservr!CMsqlExecContext::ExecuteStmts<1,1>+0x28d
  • Anonymous
    October 24, 2010
    You need to use a parameter with the k command such a 'v' or 'b' --> kv.  This will return the first 3 parameters passed to the function call.For information enter the following into windbg:  .hh k
  • Anonymous
    October 24, 2010
    I realized this post didn't contain the build of SQL Server.  The dump in this post was from SQL Server 2008 RTM:Microsoft SQL Server 2008 (RTM) - 10.0.1600.22 (X64)
         Jul  9 2008 14:17:44 
         Copyright (c) 1988-2008 Microsoft Corporation
         Enterprise Edition (64-bit) on Windows NT 6.1 <X64> (Build 7600: )Function signatures can change between versions of any program.
  • Anonymous
    October 24, 2010
    The comment has been removed
  • Anonymous
    October 24, 2010
    The comment has been removed
  • Anonymous
    October 24, 2010
    The comment has been removed
  • Anonymous
    July 31, 2013
    The comment has been removed
  • Anonymous
    August 07, 2013
    Sebastian -Your post is an interesting post for academic study, but as I'm sure you are aware Microsoft does not support hooking into SQL Server APIs using these methods.  You can read more here:support.microsoft.com/.../920925I do not recommend it.-Jay