April 19, 2010 at 6:15 pm
I have been looking at several execution plan on SQL Server. However, I am not quite sure what factors/specifics I should be looking? Bascially, I want to know what I should be concerned about when looking at the execution plan.
April 19, 2010 at 10:56 pm
Huge subject. Please take a look at this:
http://www.sqlservercentral.com/articles/books/65831/
...note the free eBook download. The author is a regular here on SSC.
April 20, 2010 at 6:33 am
Like Paul says, huge topic. The simple answers are frequently enough wrong, but still a good starting point.
Look for scans, index or table, these are frequently, but not always, an issue
Look for fat pipes or arrows, these indicate lots of data being moved. Again, not always a problem because sometimes, you're moving a lot of data, but if you see a million rows being processed but the output is 10 rows, you have a problem.
Look for extra operations, for example, the query has no ORDER BY clause, but you see a sort operator, probably setting up data for a merge operator, this can be a performance hit.
There's more, lots more. The book doesn't even cover a healthy chunk of the possibilities, but it will hopefully help to get you started.
"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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