Re: Relation between RAM / shmmax / shmall / shared_buffers

Balkrishna Sharma wrote:
> 1. Keeping the kernel parameter kernel.shmmax at 75% of RAM (i.e. at
> 3GB )kernel.shmmax = 3221225472
> 2. Keeping the kernel parameter shmall at the same value. Because
> shmall is measured in number of pages and each page on my linux is
> 4096 bytes, having kernel.shmall = 786432 (786432 * 4096 =
> 3221225472, same as shmmax)

There's little reason to put shmmax at over 50% of RAM, because
shared_buffers is going to be significantly lower than that even. I use
the attached script for this job now; I got sick of doing the math
manually all the time. If you're on a system that supports returning
memory info using getconf, it outputs the lines you need to put into the
kernel configuration.

--
Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.us