Re: shared_buffer optimization - Mailing list pgsql-performance

From Christopher Browne
Subject Re: shared_buffer optimization
Date
Msg-id 87u04nv2q6.fsf@wolfe.cbbrowne.com
Whole thread Raw
In response to shared_buffer optimization  (Ruben Rubio <ruben@rentalia.com>)
Responses Re: shared_buffer optimization
Re: shared_buffer optimization
List pgsql-performance
Quoth ruben@rentalia.com (Ruben Rubio):
> Hi, I have a question with shared_buffer.
>
> Ok, I have a server with 4GB of RAM
> -----
> # cat /proc/meminfo
> MemTotal:      4086484 kB
> [...]
> -----
>
> So, if I want to, for example, shared_buffer to take 3 GB of RAM then
> shared_buffer would be 393216 (3 * 1024 * 1024 / 8)
>
> Postmaster dont start.
> Error: FATAL:  shmat(id=360448) failed: Invalid argument
>
>
> I can set a less value, but not higher than 3 GB.
>
> Am I doing something wrong?
> Any idea?

Yes, you're trying to set the value way too high.

The "rule of thumb" is to set shared buffers to the lesser of 10000
and 15% of system memory.  In your case, that would be the lesser of
10000 and 78643, which is 10000.

I'm not aware of any actual evidence having emerged that it is of any
value to set shared buffers higher than 10000.
--
let name="cbbrowne" and tld="acm.org" in name ^ "@" ^ tld;;
http://linuxdatabases.info/info/x.html
Rules of the Evil Overlord #25.  "No matter how well it would perform,
I  will never  construct any  sort  of machinery  which is  completely
indestructible  except  for   one  small  and  virtually  inaccessible
vulnerable spot." <http://www.eviloverlord.com/>

pgsql-performance by date:

Previous
From: Jeff Trout
Date:
Subject: Re: Postgresql Performance on an HP DL385 and SmartArray 642
Next
From: "Steve Poe"
Date:
Subject: Re: Postgresql Performance on an HP DL385 and