Message-ID: <4DBECB5C.20104@2ndQuadrant.com>
Date: Mon, 02 May 2011 11:18:52 -0400
From: Greg Smith <greg@2ndQuadrant.com>
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To: pgsql-performance@postgresql.org
Subject: Re: The right SHMMAX and FILE_MAX
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On 05/02/2011 12:53 AM, Adarsh Sharma wrote:
> I am also in need of a proper documentation that explains how to set  
> SHMAX and SHMALL variables in Postgres.
>
> What things need to be taken in consideration before doing that ?
> What is the value of SHMAX & SHMALL if u have 16 GB RAM for Postgres 
> Server ?

Running the script I provided on a Linux server with 16GB of RAM:

$ cat /proc/meminfo | grep MemTotal
MemTotal:       16467464 kB

$ getconf PAGE_SIZE
4096

$ ./shmsetup
# Maximum shared segment size in bytes
kernel.shmmax = 8431341568
# Maximum number of shared memory segments in pages
kernel.shmall = 2058433

That sets SHMMAX to 50% of total RAM, which should be sufficient for any 
reasonable installation of PostgreSQL.  shmmall is a similar limit 
expressed in system pages instead, so as seen here you have to divide by 
the system page size of 4096 to figure it out.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books