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Re: PostgreSQL as a local in-memory cache

From: Dave Page <dpage(at)pgadmin(dot)org>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Dimitri Fontaine <dfontaine(at)hi-media(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, postgres performance list <pgsql-performance(at)postgresql(dot)org>
Subject: Re: PostgreSQL as a local in-memory cache
Date: 2010-06-23 20:27:38
Message-ID: AANLkTimxDE1PRSaIhLFqRfaXoG7zxbDNH9mQO4aK4Kkt@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Wed, Jun 23, 2010 at 9:25 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Wed, Jun 23, 2010 at 3:37 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>> Tom Lane wrote:
>>> Dimitri Fontaine <dfontaine(at)hi-media(dot)com> writes:
>>> > Josh Berkus <josh(at)agliodbs(dot)com> writes:
>>> >> a) Eliminate WAL logging entirely
>>
>> If we elimiate WAL logging, that means a reinstall is required for even
>> a postmaster crash, which is a new non-durable behavior.
>>
>> Also, we just added wal_level = minimal, which might end up being a poor
>> name choice of we want wal_level = off in PG 9.1.  Perhaps we should
>> have used wal_level = crash_safe in 9.0.
>>
>> I have added the following TODO:
>>
>>        Consider a non-crash-safe wal_level that eliminates WAL activity
>>
>>            * http://archives.postgresql.org/pgsql-performance/2010-06/msg00300.php
>
> I don't think we need a system-wide setting for that.  I believe that
> the unlogged tables I'm working on will handle that case.

Aren't they going to be truncated at startup? If the entire system is
running without WAL, we would only need to do that in case of an
unclean shutdown wouldn't we?


-- 
Dave Page
EnterpriseDB UK: http://www.enterprisedb.com
The Enterprise Postgres Company

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