FIX: Some queries that have a left outer join and an IS NULL filter run slower after you install SQL Server 2000 post-SP3 hotfix (830887)


The information in this article applies to:

  • Microsoft SQL Server 2000 Developer Edition
  • Microsoft SQL Server 2000 Standard Edition
  • Microsoft SQL Server 2000 Enterprise Edition
  • Microsoft SQL Server 2000 Personal Edition
  • Microsoft SQL Server 2000 Enterprise Evaluation Edition
  • Microsoft SQL Server 2000 Workgroup Edition
  • Microsoft SQL Server 2000 Desktop Engine (MSDE)
  • Microsoft SQL Server 2000 Developer Edition 64 bit
  • Microsoft SQL Server 2000 Enterprise Edition 64-bit
Bug #: SHILOH_BUGS (470434)

SYMPTOMS

A query may run slower against Microsoft SQL Server 2000 post-SP3 hotfix build 8.00.0776 or later when compared to queries that run against SQL Server 2000 before hotfix build 8.00.0776, if the following conditions are true:
  • The query involves a left outer join of two tables. In the following example, table 1 is the left table and table 2 is the right table.
  • An IS NULL filter condition exists on a column for the right table (table 2).
  • The joining columns have different data types. One column is of type varchar/char, and the other column is of type nvarchar/nchar.
  • Very few of the query result rows satisfy the ON condition of the outer join.
For example, a query that contain the following join and filter condition may run slower:
t1 left outer join t2 on t1.c1 = t2.c1 where t2.c1 is null --t1.c1 is of type nvarchar and t2.c1 is of type varchar

CAUSE

This problem occurs because the SQL Server optimizer underestimates the number of rows that satisfies the IS NULL filter condition after the join.

WORKAROUND

To work around this problem, make sure that the joining columns are of the same data type.

RESOLUTION

Service pack information

To resolve this problem, obtain the latest service pack for Microsoft SQL Server 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

290211 How to obtain the latest SQL Server 2000 service pack

Hotfix information

The English version of this hotfix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel. 
   Date         Time   Version            Size    File name
   --------------------------------------------------------------------
   31-May-2003  16:45  2000.80.818.0      78,400  Console.exe      
   28-Oct-2003  02:21  2000.80.873.0     315,968  Custtask.dll     
   02-Oct-2003  18:59  2000.80.867.0      33,340  Dbmslpcn.dll     
   25-Apr-2003  00:12                    786,432  Distmdl.ldf
   25-Apr-2003  00:12                  2,359,296  Distmdl.mdf
   29-Jan-2003  23:55                        180  Drop_repl_hotfix.sql
   12-Sep-2003  01:26  2000.80.859.0   1,905,216  Dtspkg.dll       
   26-Aug-2003  18:16  2000.80.854.0     528,960  Dtspump.dll      
   23-Jun-2003  20:40  2000.80.837.0   1,557,052  Dtsui.dll        
   23-Jun-2003  20:40  2000.80.837.0     639,552  Dtswiz.dll       
   24-Apr-2003  00:51                    747,927  Instdist.sql
   02-May-2003  23:56                      1,581  Inst_repl_hotfix.sql
   08-Feb-2003  04:40  2000.80.765.0      90,692  Msgprox.dll      
   01-Apr-2003  00:07                      1,873  Odsole.sql
   04-Apr-2003  23:46  2000.80.800.0      62,024  Odsole70.dll     
   07-May-2003  18:41  2000.80.819.0      25,144  Opends60.dll     
   02-Apr-2003  19:48  2000.80.796.0      57,904  Osql.exe         
   02-Apr-2003  21:15  2000.80.797.0     279,104  Pfutil80.dll     
   04-Aug-2003  16:17                    550,780  Procsyst.sql
   11-Sep-2003  22:37                     12,305  Qfe469315.sql
   22-May-2003  20:57                     19,195  Qfe469571.sql
   05-Sep-2003  23:36                  1,090,932  Replmerg.sql
   06-Sep-2003  05:18  2000.80.858.0     221,768  Replprov.dll     
   06-Sep-2003  05:18  2000.80.858.0     307,784  Replrec.dll      
   05-Sep-2003  22:00                  1,087,150  Replsys.sql
   13-Aug-2003  14:28                    986,603  Repltran.sql
   21-Oct-2003  22:08  2000.80.871.0      57,916  Semnt.dll        
   29-Jul-2003  18:13  2000.80.819.0     492,096  Semobj.dll       
   31-May-2003  16:27  2000.80.818.0     172,032  Semobj.rll
   05-Aug-2003  19:06                    127,884  Sp3_serv_uni.sql
   31-May-2003  23:01  2000.80.818.0   4,215,360  Sqldmo.dll       
   07-Apr-2003  15:44                     25,172  Sqldumper.exe    
   19-Mar-2003  16:20  2000.80.789.0      28,672  Sqlevn70.rll
   27-Sep-2003  02:42  2000.80.865.0     180,792  Sqlmap70.dll     
   03-Sep-2003  00:56  2000.80.857.0     188,992  Sqlmmc.dll       
   02-Sep-2003  21:03  2000.80.857.0     479,232  Sqlmmc.rll
   21-Oct-2003  22:08  2000.80.871.0     401,984  Sqlqry.dll       
   08-Feb-2003  04:40  2000.80.765.0      57,920  Sqlrepss.dll     
   28-Oct-2003  02:21  2000.80.873.0   7,606,353  Sqlservr.exe     
   25-Jul-2003  19:44  2000.80.845.0     590,396  Sqlsort.dll      
   08-Feb-2003  04:40  2000.80.765.0      45,644  Sqlvdi.dll       
   02-Oct-2003  18:59  2000.80.867.0      33,340  Ssmslpcn.dll     
   31-May-2003  23:01  2000.80.818.0      82,492  Ssnetlib.dll     
   31-May-2003  23:01  2000.80.818.0      25,148  Ssnmpn70.dll     
   28-Oct-2003  02:21  2000.80.873.0     123,456  Stardds.dll      
   31-May-2003  23:01  2000.80.818.0     158,240  Svrnetcn.dll     
   31-May-2003  16:59  2000.80.818.0      76,416  Svrnetcn.exe     
   30-Apr-2003  21:52  2000.80.816.0      45,132  Ums.dll          
   01-Jul-2003  22:19  2000.80.834.0      98,816  Xpweb70.dll
Note Because of file dependencies, the most recent hotfix or feature that contains these files may also contain additional files.

STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section of this article.

This problem was first corrected in Microsoft SQL Server 2000 Service Pack 4.

MORE INFORMATION

After you install the hotfix that is described in this article, you must make sure that trace flag 9209 is turned on when you start SQL Server. For this fix to take effect, you must have trace flag 9209 turned on when you start SQL Server. To do so, follow these steps:
  1. Start SQL Server Enterprise Manager.
  2. Right-click the instance of SQL Server, and then click Properties.
  3. Click the General tab, and then click Startup Parameters.
  4. In the Startup Parameters dialog box, type -T9209 in Parameter box, click Add, and then click OK.
  5. In the SQL Server Properties dialog box, click OK.
  6. Restart SQL Server.

Data type conversions (in this case, when an nvarchar/nchar column is compared to a varchar/char column) on a column in a query may have an adverse effect on the query's performance, and it is a good idea to avoid doing so if you can. If you use data type conversions, SQL Server may not be able to accurately produce cardinality estimates. SQL Server may also be restricted from using appropriate indexes. For additional information about data type conversions, click the following article number to view the article in the Microsoft Knowledge Base:

271566 PRB: SQL Server comparisons between columns and constants with different data types

Modification Type:MinorLast Reviewed:10/25/2005
Keywords:kbHotfixServer kbQFE kbQFE kbSQLServ2000preSP4fix kbfix kbbug KB830887 kbAudDeveloper
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