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Explain Plan vs Trace STAT lines - Webinar Question on 5/22/07

The case study in the Performance Testing Fundamentals webinar showed that the EXPLAIN PLAN estimated the UPDATE would affect 33,303 rows, but it actualy affected 80,000 rows (as shown in the STAT lines from the trace data).  Can I use this information to help me problem solve in any way?  If so, how?
Becky Goodman Send private email
Tuesday, May 22, 2007
 
 
You can compare the estimates of the EXPLAIN PLAN to the actual STAT line row actuals to help show the presence of skew or any anomolies in the cardinality/selectivity estimates made by the optimizer.  If the numbers are very different, the optimizer may have made an improper plan choice based on the estimates.  You would use this information to determine if you need histogram statistics to be added or if you need to re-evaluate how the query is written so that the optimizer could more easily calculate selectivity.
Karen Morton Send private email
Tuesday, May 22, 2007
 
 

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