Re: Postgres tiene alguna recomendacion para la variable SHMMAX

On Fri, Aug 06, 2004 at 06:05:29PM -0500, tgutierrez(at)unipamplona(dot)edu(dot)co wrote:
> Saludos..
>
> No he visto que configuren la variable SHMMAX más de 256 MB
> Trabajan con 32, 64, 128 y 256
>
> En este enlace muestran que esa variable es muy importante en postgresql
> y Me gustaria saber de que depende la configuracion de esa Variable si de
> la memosria swap, la memoria ram... o de que especificamente...
>
> http://developer.postgresql.org/docs/postgres/kernel-resources.html

Bueno, en ese mismo enlace se explica cual es la importancia de SHMMAX

The most important shared memory parameter is SHMMAX, the maximum size,
in bytes, of a shared memory segment. If you get an error message from
shmget like Invalid argument, it is possible that this limit has been
exceeded. The size of the required shared memory segment varies both
with the number of requested buffers (-B option) and the number of
allowed connections (-N option), although the former is the most
significant. (You can, as a temporary solution, lower these settings to
eliminate the failure.) As a rough approximation, you can estimate the
required segment size by multiplying the number of buffers and the block
size (8 kB by default) plus ample overhead (at least half a megabyte).
Any error message you might get will contain the size of the failed
allocation request.

Como ves no tiene nada que ver con ningun parametro fisico o de
configuracion del sistema operativo. Depende de la cantidad de buffers.

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
Bob [Floyd] used to say that he was planning to get a Ph.D. by the "green
stamp method," namely by saving envelopes addressed to him as 'Dr. Floyd'.
After collecting 500 such letters, he mused, a university somewhere in
Arizona would probably grant him a degree. (Don Knuth)