Hello,
Recently, I noticed quite strange behaviour of execution plan for a query which processes data in batches ca. 10000 records. The query joins two very large tables (ca. 20 mln and 160mln) by using indexes. At the beginning query execution plan was perfect, database engine was using only index seeks and execution of the query was not longer that 200ms.
When the batch process reached 90% of the records which have to be computed (ca. 20mln) query execution plan instantly changed and index operator on the bigger table started to use index scan, I do not have to mention that execution times increased 1000 times. I thought that statistic or indexes could not have been updated so I did both suitable thinks which came to my mind: update statistic and de-fragment of the index. It just helped for very short time.
What else could I do to come back to previous efficient execution plan?
I would like to add that database server (version 2000) is not overloaded by other heavy process, tables are not changed very often and the same batch process works fine on SQL Server 2008.
Thanks in advance,
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