Re: SHMMAX value

On Wednesday 27 June 2001 12:47, Thalis A. Kalfigopoulos wrote:
> This was asked repeatedly the past 2 weeks. With regard to "what is a sane
> value for shmmax in the kernel?" Oracle's recommendation is to go for
> 0.5*physical_memory. So I gues that 0.25*physical_memory for Pg should be
> fine.

It is entirely dependent upon the load the machine is under, and what else is
running on the machine, as well as the size of the dataset.

For some servers and datasets the kernel default is 'sane' -- for others, it
is not.

I've run PostgreSQL for almost 4 years --- and I've yet to need to change
SHMMAX from the defaults. But I am using AOLserver, which puts far less load
on a database server than other webservers or cther clients for the same
number of simultaneous connects. And it is an Intranet system -- not heavily
loaded, either.

But, beyond that, the question has in fact been answered before. See the
archives. Or just use this formula:
SHMMAX>dataset-size for highest performance. The idea is to get the whole
database in RAM. Barring that, you want to get enough SHM to do the largest
sort/join you have entirely in RAM.
--
Lamar Owen
WGCR Internet Radio
1 Peter 4:11