October 27, 2011 at 10:12 am
L' Eomot Inversé (10/27/2011)
it would have been even better if instead of "executes" it had said "is invoked" or "is called" or something similar, since "executes" leaves us guessing as to the meaning (as I said, it's the computer not the iterator that executes).
Quite agree - it was the wording that tricked so many people... a shame as it was a good question 😉
October 27, 2011 at 10:33 am
SQLRNNR (10/27/2011)
Gianluca Sartori (10/27/2011)
LadyRuna (10/27/2011)
I got it right, but only because I've read Grant Fritchey's book about execution plans. 🙂Ouch! I read that book as well.
I'm totally hopeless.
Ha - I was trying to remember where I had learned that. Maybe it was Grants book.
I think that all people who answered correctly should pool their money and buy Grant a really decent bottle.
October 27, 2011 at 1:11 pm
Gianluca Sartori (10/27/2011)
LadyRuna (10/27/2011)
I got it right, but only because I've read Grant Fritchey's book about execution plans. 🙂Ouch! I read that book as well.
I'm totally hopeless.
I also read that book...and still missed this one. Better go back and re-read.
Great question.
Rob Schripsema
Propack, Inc.
October 27, 2011 at 2:08 pm
Michael Lysons (10/27/2011)
And, more importantly, congrats on winning the Webb Ellis, SQL Kiwi!
Still celebrating here!
Paul White
SQLPerformance.com
SQLkiwi blog
@SQL_Kiwi
October 27, 2011 at 2:09 pm
Another great question Paul with very interesting lesson behind it. Cheers mate!
October 27, 2011 at 2:11 pm
Hugo Kornelis (10/27/2011)
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.
It must have been Rob Farley - I remember he came up with that memorable way of expressing it last year sometime.
Paul White
SQLPerformance.com
SQLkiwi blog
@SQL_Kiwi
October 27, 2011 at 2:51 pm
As with others, I certainly don't mind getting a question wrong when I learn from it. At least I have lots of company!! 😛
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October 27, 2011 at 6:32 pm
I'm going to have to be a dissenting voice, I agree with Paul as to the nature of 'executes first'. It's what starts the chain, and begins the process.
Thanks for an excellent question Paul, though I was in utter shock at first. I need a sammich, a beer, and an hour or two with these references methinks.
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October 27, 2011 at 7:42 pm
I answered anything because I know nothing about the execution plan but I wanted to see the answer and read the discussion now, so I tried something... and got no luck: my answer was wrong and I still don't understand... So, here I am, with my question: is it important to undersand if you are (well, trying to be) a developper on a very small database?
October 27, 2011 at 9:10 pm
tilew-948340 (10/27/2011)
I answered anything because I know nothing about the execution plan but I wanted to see the answer and read the discussion now, so I tried something... and got no luck: my answer was wrong and I still don't understand... So, here I am, with my question: is it important to undersand if you are (well, trying to be) a developper on a very small database?
It is very important if you are trying to design a query optimiser, but not many people do that. It is somewhat important if you are trying to write queries that are efficient - because you need to have some idea of how they execute, and if you can't read and understand a query plan and see how it works that can be difficult. If you are working on an OLTP system that runs on a vastly oversized platform, so that query efficiency isn't of any interest, it's not the least bit important.
So maybe the case for most people is that it is somewhat important. (For me it used to be extremely important, but in those days I was building a data engine.)
Actually it's not something that's difficult. If you have any knowledge of lazy functional languages (like Hope+ or Haskell or LML) you will understand about demand driven execution, and that's pretty much what is going on here.
Alternatively, think of it as a very simple programme paradigm: the thing that produces the result calls the things that provide it with data, and those things all call other things that give them the data they need to produce their results, and so on. Apart from the top level, nothing produces any data or does anything at all unless it is asked to by something at the level above.
Tom
October 28, 2011 at 2:57 am
Fantastic question, thanks!
Need an answer? No, you need a question
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October 28, 2011 at 4:48 am
L' Eomot Inversé (10/27/2011)
tilew-948340 (10/27/2011)
... is it important to undersand if you are (well, trying to be) a developper on a very small database?... So maybe the case for most people is that it is somewhat important. (For me it used to be extremely important, but in those days I was building a data engine.)
Alternatively, think of it as a very simple programme paradigm: the thing that produces the result calls the things that provide it with data, and those things all call other things that give them the data they need to produce their results, and so on. Apart from the top level, nothing produces any data or does anything at all unless it is asked to by something at the level above.
I didn't even know how to get the execution plan so I did some reseach and find it (CTRL-L ! simple as that!). Writes many sample query and now I understand! Yéééé!
Thanks for your answer :kiss:
October 28, 2011 at 11:08 am
Hugo Kornelis (10/27/2011)
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.
Indeed it was Rob Farley. I had the honor to be in the room with both of you when he said it.
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October 28, 2011 at 2:52 pm
gary.rumble (10/28/2011)
Hugo Kornelis (10/27/2011)
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.
Indeed it was Rob Farley. I had the honor to be in the room with both of you when he said it.
Thanks, Gary (and Paul).
I'll try to remember this so I can attribute the quote properly if -no, make that when- I steal it again.
October 30, 2011 at 4:26 pm
Yeah - that's my line. I'm pleased it's helping people remember this important aspect of how to read execution plans.
Rob Farley
LobsterPot Solutions & Adelaide SQL Server User Group
Company: http://www.lobsterpot.com.au
Blog: http://blogs.lobsterpot.com.au
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