Re: How much memory do we need ?

pavergne_at_hotmail.com wrote:
: Hello,
: We are running Oracle 7.3 on an E3000 server with 512Mb of RAM. we have 250
: ORACLE sessions, and we want to know if we have enough RAM on the machine.
: Does anybody knows how much RAM we need for all these ORACLE sessions.
: Somebody told me that ORACLE needs 4mb per session. Is it true ?

When I size servers I usually use the following rules:

128MB RAM for the O/S.
128MB RAM for the database engine and instance. 2-8MB RAM per user, depending on the application.

This usually results in a overconfiged server, but I've never met a DBA who complained about having too much RAM. Using these numbers you would need somewhere between 768MB and 2560MB in RAM for the server. For most applications 768 would be sufficient, but sometimes you run across an application who's a real memory pig. I'm a big fan of keeping procedural objects and LOV tables in physical memory, and it's always nice when your query is returned from the shared pool instead of reading from disk.

One thing that's really important, is to set aside some memory for the operating system, utilities and shells. Never include all of your memory in the SGA, always hold back at least 128MB for the O/S. You aren't really buying yourself any advantage by making your SGA so big that you start dipping into the swap file. However if I had to make a choice between more memory or more I/O paths I'd always take the I/O. Unless you have a really small amount of RAM (<=256MB), you're far more likely to be I/O bound than RAM or CPU constrained.

Also bear in mind that these are blatent swags, given in general terms without really knowing anything about your application, your I/O config, or your users usage patterns. These are the numbers that I normally go on, but they are always adjusted as the situtation dictates. This is my starting point, not the finish line.

 -Mark Weghorst Received on Fri Oct 09 1998 - 16:43:50 CDT