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Re: 2nd Level Buffer Cache

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Jim Nasby <jim(at)nasby(dot)net>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, rsmogura <rsmogura(at)softperience(dot)eu>, PG Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: 2nd Level Buffer Cache
Date: 2011-03-24 20:59:10
Message-ID: AANLkTiktwL=AUCucv6=VqVzfx+AP8hxf8g-eYoa1NMP1@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, Mar 23, 2011 at 6:12 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> It looks like the only way anything can ever get put on the free list
>> right now is if a relation or database is dropped.  That doesn't seem
>> too good.
>
> Why not?  AIUI the free list is only for buffers that are totally dead,
> ie contain no info that's possibly of interest to anybody.  It is *not*
> meant to substitute for running the clock sweep when you have to discard
> a live buffer.

It seems at least plausible that buffer allocation could be
significantly faster if it need only pop the head of a list, rather
than scanning until it finds a suitable candidate.  Moving as much
buffer allocation work as possible into the background seems like it
ought to be useful.

Granted, I've made no attempt to code or test this.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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