Re: The right SHMMAX and FILE_MAX

Tomas Vondra wrote:
> Dne 2.5.2011 06:53, Adarsh Sharma napsal(a):
>
>> 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 ?
>>
>
> Well, those two values actually define kernel limits for shared memory
> segments (i.e. memory shared by multiple processes, in this case the
> postmaster proces and backends). So it's rather a question of tuning
> shared_buffers (because that's the shared memory segment) and then
> setting those two values.
>

When I was tuning Postgresql for best Performance, I set my
shared_buffers= 4096 MB as I set 25% of RAM ( 1/4 )

So Do I need to set my SHMMAX =4096 MB.

What is the SHMALL size now ?

> SHMMAX - max. size of a single shared segment (in bytes)
> SHMALL - total size of shared segments (in pages, page is usually 4kB)
>
> So if you decide you want 1GB shared buffers, you'll need at least this
>
> SHMMAX = 1024 * 1024 * 1024 (i.e. 1GB)
> SHMALL = 1024 * 256 (1GB in 4kB pages)
>
> (althouth the SHMALL should be higher, as there will be other processes
> that need shared memory).
>
> There's a lot of docs about this, e.g. this one (it's mostly for Oracle,
> but it describes the shared memory quite nicely):
>
> http://www.puschitz.com/TuningLinuxForOracle.shtml#SettingSharedMemory
>
> regards
> Tomas
>
>