FIX: SQL Server underestimates the cardinality of a query expression and query performance may be slow

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Bug #: 469592 (SQL Server 8.0)
Under certain conditions, Microsoft SQL Server 2000 may underestimate the cardinality of a query expression. This problem may cause slow query performance. To resolve this problem, install the hotfix that is described in the "Resolution" section, and then turn on trace flag 9207.

For more information about the latest service pack for Microsoft SQL Server 2000, 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
SQL Server may underestimate the cardinality of a query expression, and query performance may be slow. This problem occurs if all the following conditions are true:
  • The predicate is made up of at least two conditions on different columns in the same table that are used together with the AND operator.
  • One of the predicates involves an inequality operator or a range expression.
  • The SQL Server query optimizer can obtain a multicolumn density from an index or from multicolumn statistics that involve the columns in the query expression.
  • A histogram that can be used to estimate the selectivity of the range expression exists, and the histogram's selectivity is less than or equal to the average selectivity of any arbitrary constant value.
Under these conditions, SQL Server may effectively apply the selectivity of the range expression two times by first using the multicolumn density for all the columns, and then by filtering based on the selectivity of the individual range expression. For example, the following query expression meets all the conditions:
SELECT a.col1, a.col2, a.col3, a.col4WHERE a.col1 = ‘x’ AND a.col2 = ‘y’ AND a.col3 = ‘z’ AND a.col4 BETWEEN ‘a’ AND ‘b’

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  06:15  2000.80.818.0      78,400  Console.exe         02-Oct-2003  08:29  2000.80.867.0      33,340  Dbmslpcn.dll        24-Apr-2003  13:42                    786,432  Distmdl.ldf   24-Apr-2003  13:42                  2,359,296  Distmdl.mdf   29-Jan-2003  13:25                        180  Drop_repl_hotfix.sql   11-Sep-2003  14:56  2000.80.859.0   1,905,216  Dtspkg.dll          26-Aug-2003  07:46  2000.80.854.0     528,960  Dtspump.dll         23-Jun-2003  10:10  2000.80.837.0   1,557,052  Dtsui.dll           23-Jun-2003  10:10  2000.80.837.0     639,552  Dtswiz.dll          23-Apr-2003  14:21                    747,927  Instdist.sql   02-May-2003  13:26                      1,581  Inst_repl_hotfix.sql   07-Feb-2003  18:10  2000.80.765.0      90,692  Msgprox.dll         31-Mar-2003  13:37                      1,873  Odsole.sql   04-Apr-2003  13:16  2000.80.800.0      62,024  Odsole70.dll        07-May-2003  08:11  2000.80.819.0      25,144  Opends60.dll        02-Apr-2003  09:18  2000.80.796.0      57,904  Osql.exe            02-Apr-2003  10:45  2000.80.797.0     279,104  Pfutil80.dll        04-Aug-2003  05:47                    550,780  Procsyst.sql   11-Sep-2003  12:07                     12,305  Qfe469315.sql   22-May-2003  10:27                     19,195  Qfe469571.sql   05-Sep-2003  13:06                  1,090,932  Replmerg.sql   05-Sep-2003  18:48  2000.80.858.0     221,768  Replprov.dll        05-Sep-2003  18:48  2000.80.858.0     307,784  Replrec.dll         05-Sep-2003  11:30                  1,087,150  Replsys.sql   13-Aug-2003  03:58                    986,603  Repltran.sql   21-Oct-2003  11:38  2000.80.871.0      57,916  Semnt.dll           29-Jul-2003  07:43  2000.80.819.0     492,096  Semobj.dll          31-May-2003  05:57  2000.80.818.0     172,032  Semobj.rll   05-Aug-2003  08:36                    127,884  Sp3_serv_uni.sql   31-May-2003  12:31  2000.80.818.0   4,215,360  Sqldmo.dll          07-Apr-2003  05:14                     25,172  Sqldumper.exe       19-Mar-2003  05:50  2000.80.789.0      28,672  Sqlevn70.rll   26-Sep-2003  16:12  2000.80.865.0     180,792  Sqlmap70.dll        02-Sep-2003  14:26  2000.80.857.0     188,992  Sqlmmc.dll          02-Sep-2003  10:33  2000.80.857.0     479,232  Sqlmmc.rll   21-Oct-2003  11:38  2000.80.871.0     401,984  Sqlqry.dll          07-Feb-2003  18:10  2000.80.765.0      57,920  Sqlrepss.dll        21-Oct-2003  11:38  2000.80.871.0   7,602,257  Sqlservr.exe        25-Jul-2003  09:14  2000.80.845.0     590,396  Sqlsort.dll         07-Feb-2003  18:10  2000.80.765.0      45,644  Sqlvdi.dll          02-Oct-2003  08:29  2000.80.867.0      33,340  Ssmslpcn.dll        31-May-2003  12:31  2000.80.818.0      82,492  Ssnetlib.dll        31-May-2003  12:31  2000.80.818.0      25,148  Ssnmpn70.dll        31-May-2003  12:31  2000.80.818.0     158,240  Svrnetcn.dll        31-May-2003  06:29  2000.80.818.0      76,416  Svrnetcn.exe        30-Apr-2003  11:22  2000.80.816.0      45,132  Ums.dll             01-Jul-2003  11:49  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.

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

This problem was first corrected in Microsoft SQL Server 2000 Service Pack 4.
After you install the hotfix, you must turn on trace flag 9207 for the hotfix to take effect. To turn on trace flag 9207 and to make sure that the trace flag is set when the SQL Server service starts, add trace flag 9207 as a SQL Server startup parameter. To do so, follow these steps:
  1. Start SQL Server Enterprise Manager.
  2. Expand SQL Server Group, and then click your instance of SQL Server.
  3. Right-click your instance of SQL Server, and then click Properties.
  4. Click the General tab, and then click Startup Parameters.
  5. In the Parameter text box, type -T9207.
  6. Click Add, and then click OK.
  7. Click OK.
  8. Restart the SQL Server service so that the new startup parameter can take effect.
Note Do not use the DBCC TRACEONTransact-SQL statement as an alternative method to set the SQL Server startup parameter. The effect of the DBCC TRACEON Transact-SQL statement maybe lost when the SQL Server service is stopped. Therefore, the trace flag may not be turned on when the SQL Server service is restarted.

When you turn on the trace flag, the SQL Server query optimizer does not include the column that has the range predicate as part of a multicolumn density match. Instead, the selectivity is applied individually by using the histogram information. In the example that is included the "Symptoms" section, if multicolumn density exists for the columns [col1, col2, col3, col4], the hotfix only uses the density of [col1, col2, col3]. The histogram that is available separately on column col4 is used appropriately.

For more information, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates
update statistics performance sample scan default

Article ID: 831302 - Last Review: 01/17/2015 05:27:40 - Revision: 2.3

  • Microsoft SQL Server 2000 Desktop Engine (Windows)
  • Microsoft SQL Server 2000 Developer Edition
  • Microsoft SQL Server 2000 Enterprise Edition
  • Microsoft SQL Server 2000 Enterprise Edition 64-bit
  • Microsoft SQL Server 2000 Personal Edition
  • Microsoft SQL Server 2000 Standard Edition
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