Re: Does my server have enough memory

Greg wrote:
So I have two basic questions that I'm hoping somebody can offer some
guidelines for:
1. What should I watch to determine if we're short on memory
2. What is something out of the ordinary or something to be concerned
about (is pi > 5 bad, or don't get excited until it's over 100, for
example)

We have a p660 with 4GB RAM, 2 CPUs. It hosts an ERP application
using Oracle and some web services for user access. Our one paging
space is also 4GB. Below is a sample of vmstat -I grabbed every 5
seconds with nothing special running, just typical activity:

Greg,

First I will start by stating that I am not a AIX performance expert. I
have not taken the system performance analysis or tuning courses with
IBM, although I want to as soon as my company will send me on the
course.

On that note, there are a couple of things I noticed about the vmstat
info you published. At twopoints during the sampling, your free memory
allocation (fre) dropped to nearly zero and the CPU wait time (wa)
jumped up dramatically.

If this is typical of daily behaviour, then you defintely have a
problem. My guess is that your Oracle instances are using up all of the
available memory for some reason, which in turns causes the system to
start paging, and all the reading/writing to the disks are causing the
CPU to have to wait for the I/O to clear up.

You may want to go post this in the Oracle newsgroups and they can
suggest improvements. One thought I have is that Oracle (at least 8i
and 9i) may be spending its time trying to write archive log
information and that is affecting the performance of the system.

Try checking your alert logs in $ORACLE_HOME/rdbms/log and compare the
times that it writes a log to the times that you see the memory drop
and the CPU wait time go up. You may need an Oracle DBA rather than an
AIX Admin ;-)

Steve

.

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