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Determining working set size
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* Determining working set size
@ 2012-03-26 07:11 Peter van Hardenberg <pvh@pvh.ca>
  2012-03-27 19:58 ` Re: Determining working set size Joshua Berkus <josh@agliodbs.com>
  0 siblings, 1 reply; 2+ messages in thread

From: Peter van Hardenberg @ 2012-03-26 07:11 UTC (permalink / raw)
  To: pgsql-performance

Baron Swartz's recent post [1] on working set size got me to thinking.
I'm well aware of how I can tell when my database's working set
exceeds available memory (cache hit rate plummets, performance
collapses), but it's less clear how I could predict when this might
occur.

Baron's proposed method for defining working set size is interesting. Quoth:

> Quantifying the working set size is probably best done as a percentile over time.
> We can define the 1-hour 99th percentile working set size as the portion of the data
> to which 99% of the accesses are made over an hour, for example.

I'm not sure whether it would be possible to calculate that today in
Postgres. Does anyone have any advice?

Best regards,
Peter

[1]: http://www.fusionio.com/blog/will-fusionio-make-my-database-faster-percona-guest-blog/

-- 
Peter van Hardenberg
San Francisco, California
"Everything was beautiful, and nothing hurt." -- Kurt Vonnegut



^ permalink  raw  reply  [nested|flat] 2+ messages in thread

* Re: Determining working set size
  2012-03-26 07:11 Determining working set size Peter van Hardenberg <pvh@pvh.ca>
@ 2012-03-27 19:58 ` Joshua Berkus <josh@agliodbs.com>
  0 siblings, 0 replies; 2+ messages in thread

From: Joshua Berkus @ 2012-03-27 19:58 UTC (permalink / raw)
  To: Peter van Hardenberg <pvh@pvh.ca>; +Cc: pgsql-performance

Peter,

Check out pg_fincore.  Still kind of risky on a production server, but does an excellent job of measuring page access on Linux.

----- Original Message -----
> Baron Swartz's recent post [1] on working set size got me to
> thinking.
> I'm well aware of how I can tell when my database's working set
> exceeds available memory (cache hit rate plummets, performance
> collapses), but it's less clear how I could predict when this might
> occur.
> 
> Baron's proposed method for defining working set size is interesting.
> Quoth:
> 
> > Quantifying the working set size is probably best done as a
> > percentile over time.
> > We can define the 1-hour 99th percentile working set size as the
> > portion of the data
> > to which 99% of the accesses are made over an hour, for example.
> 
> I'm not sure whether it would be possible to calculate that today in
> Postgres. Does anyone have any advice?
> 
> Best regards,
> Peter
> 
> [1]:
> http://www.fusionio.com/blog/will-fusionio-make-my-database-faster-percona-guest-blog/
> 
> --
> Peter van Hardenberg
> San Francisco, California
> "Everything was beautiful, and nothing hurt." -- Kurt Vonnegut
> 
> --
> Sent via pgsql-performance mailing list
> (pgsql-performance@postgresql.org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-performance
> 



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