Re: Configuration Issue ? - Mailing list pgsql-performance

Thanks guys, I think we'll certainly look to get the app certified with
7.4 and 8.x but that may take a little while.   In the interim, Im
thinking of making the following changes then:-

Change Shared_buffers from 393216 to 80,000 ( ~15% of 4GB of RAM.
Server is 8GB but I want to leave space for App as well )

Set my effective_cache_size to 125,000 ( ~25% of 4GB of RAM )

Set my sort_mem to 8192

Do those numbers look a bit better?   Will probably see if we can make
these changes asap as the server is struggling a bit now, which doesn't
really make sense given how much memory is in it.

Really appreciate your help and fast turnaround on this

Mark

-----Original Message-----
From: Joshua D. Drake [mailto:jd@commandprompt.com]
Sent: 25 October 2006 22:17
To: Richard Huxton
Cc: Mark Lonsdale; pgsql-performance@postgresql.org
Subject: Re: [PERFORM] Configuration Issue ?

Richard Huxton wrote:
> Mark Lonsdale wrote:
>>
>> Hi Josh
>>
>> Thanks for the feedback, that is most usefull.  When you said one of
the
>> settings was likely killing us, was it all of the settings for
>> max_fsm_relations, max_fsm_pages, and sort_mem or just the setting
for
>> sort_mem ?
>>
>> Can you explain why the setting would be killing me :-)
>
> The sort_mem is crucial. It's memory *per sort*, which means one query
> can use several times that amount.

Worse then that it is:

((sort memory) * (number of sorts)) * (number of connections) = amount
of ram possible to use.

Now... take the following query:

SELECT * FROM foo
  JOIN bar on (bar.id = foo.id)
  JOIN baz on (baz.id = foo_baz.id)
ORDER BY baz.name, foo.salary;

Over 5 million rows... How much ram you think you just used?

>
>> The long and short is you need to upgrade to at least 7.4,
preferrably
>> 8.1.
>
> Joshua means this too. Upgrade to 7.3.16 within the next few days,
then
> test out something more recent. You should see some useful performance
> gains from 8.1.

Right. The reason I suggested 7.4 is that he gets VACUUM VERBOSE in a
reasonable fashion but of course 8.1 is better.

Sincerely,

Joshua D. Drake


>


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