RE: Calculating Physical memory for Oracle Sessions

I hit a problem similar to this but on a windows environment. Unfortunately unless we upgrade the hardware and OS were stuck with 3GB of Ram. For a rough guide I use the calculation below:  

Virtual Bytes for oracle = Process Overhead (approximately 100 MB) + Thread Stack (1 MB x #of threads) +
Total SGA + Total PGA  

One thing I noticed is that you won't be able to reach the maximum amount of memory because of fragmentation.. On windows I believe the limit is about 3.2GB but we start seeing sessions refused when total virtual memory used hits around 2.9+GB.  

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Anurag Verma Sent: Tuesday, November 28, 2006 10:28 PM To: oracle-l_at_freelists.org
Subject: Calculating Physical memory for Oracle Sessions

Hi All,

My 9.2.0.7 database has an sga size of 1.3 GB and the RAM size is 4096 MB.

We were facing a problem of memory contention yesterday due to the increased number of sessions/connections to the database.

96% of the Physical memory and 94-95% of virtual memory was used, when checked the processes in the IBM AIX server.

So when the number of sessions increased, listener stopped receiving newer connections.

The ever increasing number of sessions were taking up the memory.

Latch free contention was there and found library cache latch stats were showing large number of sleeps.

If we need to increase shared pool, memory was not available.

One option we are planning is to increase the physical memory.

So my question is how do we determine the size of the memory used for Oracle sessions.

Say for adding another 100 sessions, how much memory will it take, so that it will help us in adding more RAM in to the server.

Thanks for your thoughts on this.

Anurag  

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