August 18, 2003 at 1:36 pm
I recently inherited a datamart and in reviewing the index strategy I see there are many system generated indexes. Their names begin _WA_SYS_XXXXXXX. Can someone educate me in why these get generated and how long they are kept for. When I review a table's indexes using EM these don't show up but are in sysindexes.
August 18, 2003 at 1:40 pm
I ran into the same situation few months back... These Index are created by the SQL Setver itself to optimise the query performance based on the usage.
This feature started from SQL Server 7.0 version.
You could see my earlier posting here...
http://www.sqlservercentral.com/forum/link.asp?TOPIC_ID=11272
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August 18, 2003 at 1:56 pm
_WA.. are not indexes. They are internally kept and updated column statistics that SQL Server can use to assist a query if it finds no index on which to base the query plan for the SQL statement.
August 19, 2003 at 2:14 pm
These statistics are good indicators where indexes might enhance performance.
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