Fixing Plan Issues in the Middle of the Night

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Fixing Plan Issues in the Middle of the Night

Jovan Popovic

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August 7, 2017 at 9:40 pm

#324841

Comments posted to this topic are about the item Fixing Plan Issues in the Middle of the Night

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Arsh SSCertifiable Points: 6345 More actions · Answer 1

Hi Jovan,

Want to know the effect of recompile option with SP execution in these versions considering the introduction of the mentioned query plan enhancements.

Thanks...Arshad

Jeff Moden SSC Guru Points: 1003851 More actions · Answer 2

From the headline:
Do you hate when someone wakes you up in the middle of the night and tells you that some query is slower and you need to investigate it?

No. I actually love it. It means I get to kick someone's butt when I get into work because I will have already told them several times that it would be slow before they promoted it to production. 😉

--Jeff Moden

RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

Change is inevitable... Change for the better is not.

Helpful Links:
How to post code problems
How to Post Performance Problems
Create a Tally Function (fnTally)

Arsh SSCertifiable Points: 6345 More actions · Answer 3

Good one Jeff . I love it too ..and for the same reason 🙂

.Arshad

Jeff Moden SSC Guru Points: 1003851 More actions · Answer 4

The problem with all this automatic stuff is that it may never actually do anything to help you identify the actual root of the problem and even the alleged better plan is a train-wreck to begin with. For example, if you aren't updating statistics on large volumes of data changes, either the new or old plans could be absolutely horrible. And there may be no good plan to be had because the ORM created a non-sargable bit of code that must recompile every time it's used (like we had) and it takes 2 to 22 seconds with an average of 7 seconds to compile each time.

Yes, I agree that such automatic selection can help with occasional bad parameter sniffing but make sure this magical cure isn't giving you the nice-warm-fuzzies about things that you really should be proactively looking for and fixing instead.

--Jeff Moden

RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

Change is inevitable... Change for the better is not.

Helpful Links:
How to post code problems
How to Post Performance Problems
Create a Tally Function (fnTally)

Arsh SSCertifiable Points: 6345 More actions · Answer 5

Jeff Moden - Tuesday, August 8, 2017 10:09 PM
The problem with all this automatic stuff is that it may never actually do anything to help you identify the actual root of the problem and even the alleged better plan is a train-wreck to begin with. For example, if you aren't updating statistics on large volumes of data changes, either the new or old plans could be absolutely horrible. And there may be no good plan to be had because the ORM created a non-sargable bit of code that must recompile every time it's used (like we had) and it takes 2 to 22 seconds with an average of 7 seconds to compile each time.
Yes, I agree that such automatic selection can help with occasional bad parameter sniffing but make sure this magical cure isn't giving you the nice-warm-fuzzies about things that you really should be proactively looking for and fixing instead.

Absolutely true Jeff . Held similar views about statistics update on large volumes on a poorly designed fast increasing group of large tables (the largest is at 135 million rows increasing by over 1 million per day).Though there's a manual update every 24 hours stats become stale because of the volume of data change (not large enough for SQL server for auto update).

Arshad