10g Memory Usage: 12 GB RAM & 5000 Connections ~ Need help understanding

Hello everyone,

I'm looking for a little help explaining what's going on with my Oracle memory usage. Here are the details:

MS Server 2003 R2 x64
Oracle 10g (64-bit)
12 GB physical RAM
SGA_MAX = 10G
SGA_TARGET = 8G
Auto Memory Management ON
Shared server connections

Here is what I am seeing. On startup, with no external connections (using Perf Mon):

Private Bytes: 10.48 GB
Page File Bytes: 10.48 GB
Working Set: 0.22 GB
Virtual Bytes: 10.74 GB

So, I'm seeing all the SGA_MAX plus a few other things (PGA?) being allocated and reserved (Private Bytes). Working set is small because not much has happened yet.

I gradually ramped up to 5,000 connections over a couple of hours and let it run for a while. Using Perf Mon, I monitored the CPU and memory usage for 17 hours and see the following:

Private Bytes: 11.87 GB (Average) (Min: 11.11G, Max: 12.27G) Page File Bytes: 11.87 GB (Average) (Min: 11.11G, Max: 12.27G) Working Set: 0.92 GB (Average) (Min: 0.44G, Max: 1.18G) Virtual Bytes: 12.24 GB (Average) (Min: 11.48G, Max: 12.68G)

The Auto Memory Tuning works like a charm, adjusting the large pool to allow for the number of connections. Max UGA per connection works out to 317 KB.

I guess I need someone to explain to me why the private bytes grows. I mean, MAX_SGA is 10G, but when I check, the ASMM balances the SGA so that even though the shared and large pools have grown, the buffer cache has shrunk and it's still within 8 GB. So, that's 2 GB it's reserved for SGA, but not using. Using shared server, PGA isn't that big. So, why does the private bytes start at 10.5G and get up to 12.3G? I see the reading for "Page File" follows the Private Bytes exactly.

I used Pslist (from sysinternals) just now and it lists VM and Private VM as 4 GB for Oracle.exe.

I don't see a lot of swapping. Available memory doesn't get below 60 MB, pagefile usage is around 30%. Buffer cache hit ratio is 99.99%.

Any tutors out there who can enlighten me? :)

Thanks!
-Diana Received on Wed Jun 28 2006 - 11:34:44 CDT