FIX: Multi-Session DBCC OUTPUTBUFFER Under Stress Causes AV

ID: Q170437

The information in this article applies to:

Microsoft SQL Server versions 6.0, 6.5


BUG #: 17005 (6.5)
       15719 (6.0)

SYMPTOMS

Running frequent DBCC OUTPUTBUFFER commands from more than one concurrent session while the system is under transactional stress may cause a handled access violation (AV). After this AV, the server may stop responding. This problem happens on all versions of SQL Server from 6.00.121 through 6.50.258, but it only happens on:

SMP computers with three or more processors.

Two-processor computers with smp concurrency set to -1.

If you are running a debug server (needed for accurate stack traces on SQL Server 6.5), you can identify the problem by one of the following two call stacks from 6.50.255 debug:

The following stack is less frequent:


   debugSR!ubchkalloc+0x22
   debugSR!memshrink+0xb8
   debugSR!s_pop+0x23e
   debugSR!s_pop+0xb9
   debugSR!execproc+0x11eb
   debugSR!execrpc+0xd07

The following stack is more frequent:


   debugSR!ubfree+0x96
   debugSR!memfree+0x215
   debugSR!procfree+0xc8
   debugSR!procrm2+0x17a
   debugSR!procrm+0xd7
   debugSR!s_pop+0x22d
   debugSR!s_pop+0xb9
   debugSR!s_cleanframe+0x2fb
   debugSR!s_recompile+0x942
   debugSR!ex_raise+0x37a
   debugSR!prepscan_failed+0x23
   debugSR!prepscan+0x367
   debugSR!startscan+0x377
   debugSR!exec_substitute+0x435
   debugSR!exec_eop+0x493
   debugSR!exec_eop+0x1e2
   debugSR!execute+0x2c0
   debugSR!s_execute+0xbf8
   debugSR!sequencer+0x35c

WORKAROUND

To work around this problem, do not issue multiple concurrent DBCC OUTPUTBUFFER statements.

STATUS

Microsoft has confirmed this to be a problem in SQL Server versions 6.0 and 6.5. This problem was corrected in the latest Microsoft SQL Server 6.5 U.S. Service Pack. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces):


   S E R V P A C K

Additional query words: hang hung freeze frozen dead stopped


Keywords          : kbenv kbusage SSrvGen SSrvGPF kbbug6.50 kbfix6.50.sp4 kbbug6.00 
Version           : 6.0 6.5
Platform          : WINDOWS 
Issue type        : kbbug

Last Reviewed: April 19, 1999