May 29, 2013 at 4:33 am
Hi,
I analysed the trace file using DTA and got recommendations. And i got estimated improvement number as 79%
when i given the same trace file to analyse next time using DTA. This time it is showing Estimated improvement as 89%
I am not able to understand why the values are changing for the same trace file analysis.
May 29, 2013 at 5:07 am
The DTA works off of statistics and the indexes you have in order to make calculations to arrive at possible improvements. But, understand, statistics are simply a mathematical sampling of your data. Another way to define that is as an estimate. Another way is as a guess. Those numbers are not hard and fast, plus they're subject to change. For all these reasons, I find the DTA a very problematic approach to tuning queries in a database. It frequently misses simple fixes and it's suggestions are problematic at best. Don't simply, blindly, implement it's suggestions. Evaluate each one to ensure that it will be actually helpful.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning
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