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Re: Posix Shared Mem patch

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: A(dot)M(dot) <agentm(at)themactionfaction(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Posix Shared Mem patch
Date: 2012-06-26 23:15:26
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Excerpts from Tom Lane's message of mar jun 26 18:58:45 -0400 2012:

> Even if you actively try to configure the shmem settings to exactly
> fill shmmax (which I concede some installation scripts might do),
> it's going to be hard to do because of the 8K granularity of the main
> knob, shared_buffers.

Actually it's very easy -- just try to start postmaster on a system with
not enough shmmax and it will tell you how much shmem it wants.  Then
copy that number verbatim in the config file.  This might fail on picky
systems such as MacOSX that require some exact multiple or power of some
other parameter, but it works fine on Linux.

I think the minimum you can request, at least on Linux, is 1 byte.

> Moreover, a installation script that did that
> would soon learn not to, because of the fact that we don't worry too
> much about changing small details of shared memory consumption in minor
> releases.


Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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