Page Life Expectancy.

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Page Life Expectancy.

ben.brugman

SSChampion

Points: 13369
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August 3, 2015 at 2:13 am

#300913

Last week I monitored the Page Life Expectancy on a system.
In a while loop with a build in delay of 1 minute I did a :
SELECT '--' [--], getdate() stamp, cntr_value AS 'Page Life Expectancy'
FROM sys.dm_os_performance_counters
WHERE object_name = 'SQLServer:Buffer Manager' AND counter_name = 'Page life expectancy'
And noticed an increase of 80 seconds of a PLE in one minute.
This was outside my expectation.
I know that the PLE is a prediction. But would like to know how it it establisched.
Ben

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Grant Fritchey SSC Guru Points: 398909 More actions · Answer 1

It's just based on how long the pages have stayed in memory. So from one minute to the next, a page has stayed in memory, at least 60 seconds, so that accounts for the majority of that change. If that same page had been in memory for another 20 seconds during the previous run of your query, it wouldn't have necessarily showed up, but some other page that had been in longer than 20, but less than 80 was in there. Chances are good, if you were seeing the same page being measured for duration that it incremented by 60 seconds each time after that.

Don't get hung too much on PLE. It's just a general health indicator and not a major one at that. It shows the volatility of your memory, but not whether that volatility is something to worry about. I'd look at other memory counters such as pages/sec, page faults/sec and memory grants pending. Also use the ring buffers to look for out of memory messages and focus on your wait statistics as indicators for where the bottlenecks are.

"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

ben.brugman SSChampion Points: 13369 More actions · Answer 2

Grant Fritchey (8/3/2015)
Don't get hung too much on PLE.

Thanks for you reply.

I do tend to get hung up to much by 'numbers' in general, and like to understand how these numbers get 'established'. I should not do this, but it is in my genetics.

Thanks for your advise.

Ben

Jeff Moden SSC Guru Points: 1004406 More actions · Answer 3

ben.brugman (8/3/2015)
Grant Fritchey (8/3/2015)
Don't get hung too much on PLE.
Thanks for you reply.
I do tend to get hung up to much by 'numbers' in general, and like to understand how these numbers get 'established'. I should not do this, but it is in my genetics.
Thanks for your advise.
Ben

Actually, such intellectual curiosity is a cherished quality in superiors, peers, and subordinates. Don't ever lose that quality.

--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)

Grant Fritchey SSC Guru Points: 398909 More actions · Answer 4

Jeff Moden (8/3/2015)
ben.brugman (8/3/2015)
Grant Fritchey (8/3/2015)
Don't get hung too much on PLE.
Thanks for you reply.
I do tend to get hung up to much by 'numbers' in general, and like to understand how these numbers get 'established'. I should not do this, but it is in my genetics.
Thanks for your advise.
Ben
Actually, such intellectual curiosity is a cherished quality in superiors, peers, and subordinates. Don't ever lose that quality.

I agree. I sure wasn't attempting to squish any inquiry or attempts at understanding.

"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

ben.brugman SSChampion Points: 13369 More actions · Answer 5

Grant and Jeff,

Next to showering this weekend I finished a book, and enjoyed that very much. It does anwser a lot of questions, most questions are anwsered extensively, none of the anwsers do matter at all.

What If[/url]

For me an excellent read,

Ben