Article ID: 251094
Article Last Modified on 3/14/2006
APPLIES TO
- Microsoft SQL Server 7.0 Standard Edition
This article was previously published under Q251094
BUG #: 57007 (SQLBUG_70)
SYMPTOMS
When updating existing statistics using sampling, two things may happen:
- An Access Violation occurs during Query Optimization and the user is unable to retrieve the contents of that table using regular SELECT statements that use this index.
- In cases where an Access Violation does not occur, it is possible that the user works with sub-optimal plans.
CAUSE
When updating existing statistics for non-unique clustered indexes on variable-length columns using sampling, either default or explicit, with a sample size of less than 100%, statistics may become inconsistent. This problem may also occur if SQL Server auto-updates the statistics on this index because the Auto Update Statistics database option is set for that database.
WORKAROUND
The workaround is to implement one or more of the following:
- Clear the Auto update statistics database option.
- Update statistics for this index using the FULL SCAN option.
- Drop and recreate the index.
- Do not update statistics for this index.
STATUS
Microsoft has confirmed this to be a problem in SQL Server 7.0. This problem has been corrected in U.S. Service Pack 2 for Microsoft SQL Server 7.0. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
254561 INF: How to Obtain Service Pack 2 for Microsoft SQL Server 7.0 and Microsoft Data Engine (MSDE) 1.0
For more information, contact your primary support provider.
MORE INFORMATION
For example, consider the following table with a clustered index:
create table t (c1 varchar(15), c2 varchar(25))
go
create clustered index t_c on t(c1, c2)
go
The statement that causes inconsistent data to be generated is:
UPDATE STATISTICS t(t_c) with sample 50 percent
go
REFERENCES
For information on how to disable automatic updating of statistics for a specific index, see the Books Online topic sp_autostats (T-SQL).
Additional query words: data inconsistency, statistics, UPDATE STATISTICS
Keywords: kbbug kbfix KB251094
