| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Andrew Dunstan <andrew(at)dunslane(dot)net>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Josh Berkus <josh(at)agliodbs(dot)com> |
| Subject: | Re: Auto-tuning work_mem and maintenance_work_mem |
| Date: | 2013-10-16 20:50:30 |
| Message-ID: | CAGTBQpaX7RtWk=-TRUB-jMk1tppoxdDtR7i5xu209q=xWw0AMw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Oct 16, 2013 at 5:30 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> On Wed, Oct 16, 2013 at 04:25:37PM -0400, Andrew Dunstan wrote:
>>
>> On 10/09/2013 11:06 AM, Andrew Dunstan wrote:
>> >
>> >
>> >
>> >The assumption that each connection won't use lots of work_mem is
>> >also false, I think, especially in these days of connection
>> >poolers.
>> >
>> >
>>
>>
>> Andres has just been politely pointing out to me that my knowledge
>> of memory allocators is a little out of date (i.e. by a decade or
>> two), and that this memory is not in fact likely to be held for a
>> long time, at least on most modern systems. That undermines
>> completely my reasoning above.
>>
>> Given that, it probably makes sense for us to be rather more liberal
>> in setting work_mem that I was suggesting.
>
> Ah, yes, this came up last year (MMAP_THRESHOLD):
>
> http://www.postgresql.org/message-id/20120730161416.GB10877@momjian.us
Beware of depending on that threshold. It varies wildly among platforms.
I've seen implementations with the threshold well above 64MB.
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