Microsoft KB Archive/164970

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BUG: Disk Dumps May Cause Handled AV When Space Is Low

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Q164970

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The information in this article applies to:


 * Microsoft SQL Server version 6.0

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SYMPTOMS
Under rare circumstances, if the amount of available disk space is very low, SQL Server may generate a handled access violation (AV) when trying to dump to disk.

WORKAROUND
Make sure that there is an adequate amount of free space before dumping to the disk, or dump to a different type of dump device. Sample code is provided in the MORE INFORMATION section of this article for an extended stored procedure that you can use to determine the amount of free space before dumping to disk.

STATUS
Microsoft has confirmed this to be a problem in Microsoft SQL Server version 6.0. This problem has been corrected in Microsoft SQL Server version 6.5.

MORE INFORMATION
To assist in checking for necessary disk space before performing an automated backup, you can use an extended stored procedure to determine the amount of available disk space on the server. The documentation provides a sample procedure, xp_diskfree, that provides this capability. The following sample is similar to that function, but allows UNC drive specifications and returns the result as an output parameter rather than a result set.

If the code were compiled into a procedure called xp_sample, the usage would be:

   declare @freespace int exec xp_sample '\\server1\share1\', @freespace output select @freespace


 * THE FOLLOWING CODE IS FOR SAMPLE USE ONLY ***

  #define MAX_SRVINT4_VALUE 2147483647 DBINT paramlength; DBCHAR rootname[_MAX_PATH]; DBCHAR bErrorMsg[2 * _MAX_PATH]; DWORD secPerCluster; DWORD bytesPerSector; DWORD freeClusters; DWORD totalClusters; DBINT space_remaining; __int64 large_calc;

//Make sure they specified drive and output param for space if (srv_rpcparams(srvproc) < 2) {        sprintf(bErrorMsg, "SYNTAX:\nDECLARE @freespace int\nexec         xp_sample ' ', "  \          "@freespace OUTPUT\n\nwhere is like         \\\\ \\ \\ or :\\"); srv_sendmsg(srvproc, SRV_MSG_ERROR, CMDSHELL_ERROR, SRV_INFO,        (DBTINYINT)0, NULL, 0, 0, bErrorMsg, SRV_NULLTERM); srv_senddone(srvproc, (SRV_DONE_ERROR | SRV_DONE_MORE), 0, 0); return(XP_ERROR); }

//Move the path specified into rootname paramlength = srv_paramlen(srvproc, 1); srv_bmove(srv_paramdata(srvproc, 1), rootname, paramlength); rootname[paramlength] = '\0'; //NULL terminate

if (GetDiskFreeSpace(rootname, &secPerCluster, &bytesPerSector, &freeClusters, &totalClusters)) {         large_calc = secPerCluster * freeClusters * bytesPerSector; }     else {        sprintf(bErrorMsg, "GetDiskFreeSpace failed with error %d "  \             "on path %s", GetLastError, rootname); srv_sendmsg(srvproc, SRV_MSG_ERROR, CMDSHELL_ERROR, SRV_INFO,           (DBTINYINT)0, NULL, 0, 0, bErrorMsg, SRV_NULLTERM);

srv_senddone(srvproc, (SRV_DONE_ERROR | SRV_DONE_MORE), 0, 0); return(XP_ERROR); }

//If we exceed 2 GB of disk space, return 2 GB free as this is     //the largest value we can pass back to an INT value if (large_calc > MAX_SRVINT4_VALUE) {        large_calc = MAX_SRVINT4_VALUE; }     space_remaining = (DBINT)large_calc;

//Return the size in the output param srv_paramset(srvproc, 2, (BYTE *)&space_remaining, 4); srv_senddone(srvproc, SRV_DONE_MORE, 0, 0); return(XP_NOERROR);

See the Programming Open Data Services documentation for further information on writing and registering extended stored procedures.

Additional query words: hard

Keywords : kbprogramming

Issue type : kbbug

Technology : kbSQLServSearch kbAudDeveloper kbSQLServ600