Re: Total size of shared memory used on a server by several Oracle instances

From: Mark Bole <makbo_at_pacbell.net>
Date: Thu, 26 Feb 2004 15:50:49 GMT
Message-ID: <tBo%b.17372$He5.1346@newssvr29.news.prodigy.com>

Bib Endum wrote:

> "rjp" <rjp.l_at_laposte.net> a écrit dans le message de
> news:9b7a7215.0402260408.d531dbf_at_posting.google.com...
>

>>Hi,
>>
>>I need to determine what amount of server shared memory I need on a
>>server with several Oracle instances ?
>>Does I simply have to sum the total sga size of all instances or is a
>>more complicated ?
>>

>
>
> I would think that you are right, if you want to know the amount of shared
> memory. By total sga size I assume you include db buffers, redo buffers,
> shared pool, etc...
>
> If you want to determine the total amount of ram used, that would be a lot
> more complicated, depending of the number of processes you have, what they
> are doing, and how they are configured.
>

In the Unix world (you didn't state which platform) the "ipcs" command shows you the total amount of OS shared memory used by each RDBMS instance. The "top" and "ps" commands also give you total and resident memory sizes for server process. Taking swap, etc into account makes this a very arcane science, about which you can probably find plenty on Google.

So if one Oracle instance shows, for example, a shared memory segment of 500 MB from ipcs, and you want to have three of these on one machine, then get at least 2 GB of physical RAM.

The other advice, of course, is to avoid running multiple instances on one physical machine and just give as much memory as possible to the single instance. Depends on your business needs.

--Mark Bole Received on Thu Feb 26 2004 - 09:50:49 CST