Re: Advice/guideline on increasing shared_buffers and kernel parameters

Hi Gnanam,


On Tue, 8 May 2012 12:22:58 +0530, Gnanakumar wrote:
> Our Production server has got 35 GB physical RAM size.   Since the
> server
> has lots of RAM, we want to really make use of it.  We've already
> configured
> "max_connections" to 1000 and "shared_buffers" to 1536 MB, but when
> we tried
> to increase only "shared_buffers" to 3072MB (keeping
> "max_connections" as it
> is), PostgreSQL failed to start with the following error:
>
>     EDTFATAL:  could not create shared memory segment: Invalid argument
>     EDTDETAIL:  Failed system call was shmget(key=5432001,
> size=3307192320, 03600).
>
> Keeping max connection property to 1000, how do I "best" tune/set up
> its
> memory related parameters (including Linux Kernel parameters --
> SHMMAX and
> SHMALL)?


did you read
http://www.postgresql.org/docs/8.2/static/kernel-resources.html ?

If it is a dedicated DB server the rule of thumb usually is to use 25%
RAM for shared buffers, but no more than 8GB unless proper benchmarking
has shown a benefit using above 8GB. But I am not sure if 8GB of shared
buffers is suitable for 8.2 at all. 8.2 is EOL btw.
Also set effective cache size to 50% RAM.

Depending on your work load you might tune work_mem,
maintenance_work_mem etc.

Also, do you really NEED 1000 concurrent sessions? IF you really do, it
might be worse to look into a connection pooler.

Here is a quite nice guide:

http://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server

hth

Jan


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