Join Operations – Nested Loops

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Join Operations – Nested Loops

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SQLRNNR SSC Guru Points: 281334 More actions · Answer 1

Lempster (1/7/2011)
Jason, thanks for the article. Just one point: after forcing the optimizer to use a Nested Loop you state,
By trying to force the optimizer to use a Nested Loops where the query didn't really warrant it, we did not improve the query and it could be argued that we caused more work to be performed.
Yet you've improved the query time (compared to when no query hint was used) by nearly 50%. Of course the logical reads have gone through the roof and that may or may not be a problem depending on the amount of memory and CPU on the box in question, but if it's just query execution time you're interested in, I would argue that you have improved it.
I definitley agree that in the vast majority of cases one should leave the optimizer to pick the 'best' plan (we should really say 'optimal' as it may take way too long to actually find the 'best' plan) and use query hints with extreme caution.
Thanks
Lempster

Good points. It was due to the increased logical reads that one may argue that more work is being done. But yes, based on execution time, you are correct.

Thanks for the comments.

Jason...AKA CirqueDeSQLeil
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Bharat Panthee Default port Points: 1448 More actions · Answer 2

Bharat Panthee

Default port

Points: 1448

January 8, 2011 at 10:39 pm

#1271102

Very nice article, Thanks !

SQLRNNR SSC Guru Points: 281334 More actions · Answer 3

Bharat Panthee (1/8/2011)
Very nice article, Thanks !

Thank you Bharat.

Jason...AKA CirqueDeSQLeil
_______________________________________________
I have given a name to my pain...MCM SQL Server, MVP
SQL RNNR
Posting Performance Based Questions - Gail Shaw[/url]
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Mark Cowne One Orange Chip Points: 26952 More actions · Answer 4

Interesting stuff, thanks!

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Deja View - The strange feeling that somewhere, sometime you've optimised this query before

How to get the best help on a forum

http://www.sqlservercentral.com/articles/Best+Practices/61537

nopeqwerty123 SSC Veteran Points: 220 More actions · Answer 5

Hi there.

I appreciate you taking the time to go in detail regarding the hows and whys of optimization in this scenario. While i cannot attest to your example at the moment, i will try in the future.

Thanks!

SQLRNNR SSC Guru Points: 281334 More actions · Answer 6

Mark-101232 (2/1/2013)
Interesting stuff, thanks!

You're welcome.

Jason...AKA CirqueDeSQLeil
_______________________________________________
I have given a name to my pain...MCM SQL Server, MVP
SQL RNNR
Posting Performance Based Questions - Gail Shaw[/url]
Learn Extended Events