New 11i install - how many nodes

Question

We are looking to install the Financials modules of 11i (AP/AR/FA/GL) and trying to decide on platform out of Red Hat Linux and AIX 5L both of which we are familiar with.
One thing that will influence this decision is the number of nodes required.
How do we decide if a single node install will suffice ?
Is this purely a performance/sizing issue, or are there other factors (ease of install/patching ?).
Is a 2 node install more standard ?
We will have approx. 40 concurrent users, we will be importing approx. 7000 AR invoice lines and 700 AP invoice lines daily.
Any advice or pointers to documents/discussions gratefully received.
Thanks,
Colin

Answer 1

OCS on Linux was one of the most miserable installations I have ever done. There was anote on Metalink that said the most important thing for installing OCS on Linux was to know what you are doing (or more to the point, what to do for every failure).
If you go with Linux, you can have up a 1.7 GB SGA. Most people set sga_target for 11i on Linux and let the database dynamically adjust db_cache_size and shared_pool size as it wants throughout operation. For 40-50 users, you should only need 1-2 GB of pga_aggregate_target.
The amount of RAM consumed by sessions is trickier to estimate. In an 11.5.10.2 instance with no users, you will have at least 100 sessions. 40-50 concurrent users will have at least 2 sessions, most likely 5 or 10, depending on how many forms they open. I see 5.6 GB of UGA/PGA memory used by 254 sessions, so that averages to about 20MB each. The amount of UGA/PGA varies drastically as some processes use very little and some use hundreds of MB. Also, each forms process tend to average about 50 MB per open form. The applications processes will need at least 2 GB for JVMs, concurrent managers etc.
When you add it all up, it is tough to fit a 50 user production 11.5.10.2 system on 8 GB of RAM. 16 GB is actually pushing it as well. I have 50-60 users on a single node 32 GB Sun V440 that usually sits around 15GB free. They have not finished implementing all products and users, so I pushed for 32 GB over 16 to avoid paging problems when they are fully utilized.