Query Plan Execution Order

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Query Plan Execution Order

Paul White

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Points: 150467
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October 26, 2011 at 9:07 pm

#245806

Comments posted to this topic are about the item Query Plan Execution Order
Paul White
SQLPerformance.com
SQLkiwi blog
@SQL_Kiwi
October 27, 2011 at 3:53 am

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Ron McCullough SSC Guru Points: 63877 More actions · Answer 1

Blew that one as did someone before me.

Learned a lot by reading your references - thanks for those.

If everything seems to be going well, you have obviously overlooked something.

Ron

Please help us, help you -before posting a question please read[/url]
Before posting a performance problem please read[/url]

antony-688446 Ten Centuries Points: 1221 More actions · Answer 2

Looks like I am the first to get it right! 😀

Makes a change.

I am normally the last person to get it wrong.

Nice question, with lots of interesting articles.

M&M SSC-Insane Points: 21700 More actions · Answer 3

M&M

SSC-Insane

Points: 21700

October 26, 2011 at 11:45 pm

#1399991

This might be the toughest QotD.

M&M

tommyh SSCertifiable Points: 6302 More actions · Answer 4

Going to stick my neck out and say that its wrong.

Yes the stream aggregate gets called first... but it hasnt finished. So is the important part which gets called first or which gets finished first? Personally i think its the part that gets finished first thats important (or more precisly the thing that performs its purpose first). I cant say a function has been executed when it hasnt actually done anything.

Could be a language thing though that i put a different meaning into "executes" then everyone else 🙂

/T

Paul White SSC Guru Points: 150467 More actions · Answer 5

tommyh (10/27/2011)
Going to stick my neck out and say that its wrong.
Yes the stream aggregate gets called first... but it hasnt finished. So is the important part which gets called first or which gets finished first? Personally i think its the part that gets finished first thats important (or more precisly the thing that performs its purpose first). I cant say a function has been executed when it hasnt actually done anything.
Could be a language thing though that i put a different meaning into "executes" then everyone else 🙂

The learning point today was about execution order (hence the title). Query plans are pipelines, and the intention was to highlight something that most people misunderstand about that. I'm sorry the way I phrased it differs from your intuitive understanding of 'executes', if I could give you your two points, I would. That's not to say that I agree with you (I don't) but points are free, and I like people to be happy 🙂

Paul White
SQLPerformance.com
SQLkiwi blog
@SQL_Kiwi

spaghettidba SSC Guru Points: 105732 More actions · Answer 6

Great question, Paul, and great explanation.

Looks like you tricked most of us (myself included).

-- Gianluca Sartori

Paul White SSC Guru Points: 150467 More actions · Answer 7

Gianluca Sartori (10/27/2011)
Great question, Paul, and great explanation.
Looks like you tricked most of us (myself included).

Thanks, but I want to say that I really really really didn't set out to trick anyone with this. It was intended as a follow-on question to my previous one (Table Access Order[/url]) but the scheduling meant they came much further apart in time than I intended. The formatting also got messed up in the explanation, but hey ho. Hopefully there's enough value in the learning point that I get away with it.

Paul White
SQLPerformance.com
SQLkiwi blog
@SQL_Kiwi

Skanker Hall of Fame Points: 3059 More actions · Answer 8

Great question. I got it wrong but learned something which is a good start to the day.

call.copse SSCoach Points: 18048 More actions · Answer 9

Nice one. I got it right - yay! - though I had to spend 20 minutes reading up (sorry work) first, as I was determined to get it right.

I think the setter was quite correct. If he had said which FINISHES executing first that would be a different matter.

Michael Lysons SSCertifiable Points: 6491 More actions · Answer 10

Great question for learning - cheers 🙂

And, more importantly, congrats on winning the Webb Ellis, SQL Kiwi!

Hugo Kornelis SSC Guru Points: 64790 More actions · Answer 11

Good question, Paul!

I had the correct answer,but only thanks to the fact that I attended SQL Saturday in Portland a few weeks back (just before the PASS Summit). I don't recall who said it, probably either Buck or Rob, but the quote itself will always stick: "Exection plans suck". Refering to the little-known fact that data is not pushed from right to left (as most people usually read plans, myself included), but pulled ("sucked") by the top-left operator from the operator to the right and below it.

Hugo Kornelis, SQL Server/Data Platform MVP (2006-2016)
Visit my SQL Server blog: https://sqlserverfast.com/blog/
SQL Server Execution Plan Reference: https://sqlserverfast.com/epr/

Britt Cluff SSCertifiable Points: 5083 More actions · Answer 12

Tough question with good references. I missed it but I learned something today.

http://brittcluff.blogspot.com/

rfr.ferrari SSCertifiable Points: 6879 More actions · Answer 13

really, it's a very good question!!!

thanks Paul!!

[font="Times New Roman"]rfr.ferrari[/font]
DBA - SQL Server 2008
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