Comments on: Swap Space in Linux and Unix

By: dbakerber

dbakerber — Tue, 12 Aug 2008 23:19:05 +0000

Excellent, glad to hear that your problem has been resolved.

By: Kuldeep Singh

Kuldeep Singh — Tue, 12 Aug 2008 23:01:39 +0000

Andrew – As promised here is the update –

1. Our Senior DBA has implemented MTS after careful consideration and we are seeing major improvement in memory/session management. The system is still under observation.

By: Kuldeep Singh

Kuldeep Singh — Thu, 31 Jul 2008 12:54:32 +0000

Andrew/Mark – Thank you for helping out here. The information above might be relevant to our current problem. We will work with the DBA staff and the system administrators. I will post what we found or otherwise…
Thanks,
Kuldeep

By: dbakerber

dbakerber — Thu, 31 Jul 2008 12:33:48 +0000

In my experience, no there is no message about swap being full. Possibly because the space is actually getting marked as used, not being physically used for swapping? You would need to talk to a Unix System administrator on that one.

The memory issue is really just an experienced guess. A 900 user system would not typically perform well in the amount memory that they have allocated. 32G is a good place to start on tuning the instance memory. However, they are on 32 bit Oracle, so they would also have to switch to 64 bit to do a lot of good.

By: Mark A. Williams

Mark A. Williams — Thu, 31 Jul 2008 04:18:26 +0000

> What is the Oracle version?

It looks like it is 8.1.7.4 based on the original posting.

> Do you understand that there is a lot more to Oracle memory usage than PGA Memory?

Yes. My question was why the recommendation to up the server memory to 32GB based upon the provided information? What in the provided information indicates that such action is necessary?

Also, if there was insufficient swap space (i.e. the swap was exhausted/filled) would there not be a message in the system logs to indicate that event?

Thanks,

Mark

By: dbakerber

dbakerber — Thu, 31 Jul 2008 03:08:10 +0000

What is the Oracle version? Do you understand that there is a lot more to Oracle memory usage than PGA Memory? PGA is only the memory that the individual user processes need to run. The remainder of the memory on the server is used in the Oracle server processes and memory segments. For a 900 user system, it would not be at all unusual to have 100+G RAM devoted to the Oracle instance. It might be a good idea to take a class on Oracle concepts, or hire a consultant to run a tuning exercise on your Oracle instance.

Oracle will not run in much less than 256M (that is, SGA_TARGET=256M). Oracle will not use more memory than it is granted by the PGA_TARGET and the SGA_MAX_SIZE or SGA_TARGET, the starting point for determining the appropriate amount of memory for your instance is the awr or statspack report.

By: Mark A. Williams

Mark A. Williams — Thu, 31 Jul 2008 01:20:30 +0000

> it would be a good idea to go to a 64 bit OS, and use about 32G RAM

Why do you suggest that? The SGA is reported to be 900MB and the “session pga memory max” is reported to be 175MB making for just over 1GB of memory usage as I see it here. Why the need to jump from 6GB of RAM on the system to 32GB RAM when Oracle looks to be using about 1GB of the existing RAM?

Thanks,

Mark

By: dbakerber

dbakerber — Wed, 30 Jul 2008 22:56:40 +0000

Realistically, to be able to handle the number of connections you are talking about, it would be a good idea to go to a 64 bit OS, and use about 32G RAM.

By: dbakerber

dbakerber — Wed, 30 Jul 2008 21:17:32 +0000

What is your Oracle version? If it is the 8.1.7.4, then you should have 12G Swap (twice RAM). If it is Oracle 10, then you need 6G swap, in either case it looks like you have insufficient allocated. I dont know how to tell which type you are using, but the simplest thing to do is to create the appropriate amount of swap space and run from there. If the problem does not happen, you are done, if it does happen again, look at the MTS settings.

By: Kuldeep Singh

Kuldeep Singh — Wed, 30 Jul 2008 21:06:36 +0000

[oracle@xxxxxxx$ swapon -s
Filename Type Size Used Priority
/dev/xxxxxx/xxxxxx partition 2097096 53204 -1

That is what it is configured to. We have 6GB RAM on a 32 bit OS. The SGA is at 900MB [approx.]. We did some analysis on user memory.

SQL> set heading off
SQL> set echo off
SQL> set feedback off
SQL> select ‘Total current memory for all sessions: ‘ || sum(value) || ‘ bytes’
2 from v$sesstat a, v$statname b
3 where name = ’session uga memory’
4 and a.statistic# = b.statistic#
5 /

Total current memory for all sessions: 92265108 bytes
SQL> select ‘Total maximam memory for all sessions: ‘ || sum(value) || ‘ bytes’
2 from v$sesstat a, v$statname b
3 where name = ’session uga memory max’
4 and a.statistic# = b.statistic#
5 /

Total maximam memory for all sessions: 127797696 bytes

SQL> select ‘Total current memory for all sessions: ‘ || sum(value) || ‘ bytes’
2 from v$sesstat a, v$statname b
3 where name = ’session pga memory’
4 and a.statistic# = b.statistic#
5 /

Total current memory for all sessions: 183325780 bytes
SQL> select ‘Total maximam memory for all sessions: ‘ || sum(value) || ‘ bytes’
2 from v$sesstat a, v$statname b
3 where name = ’session pga memory max’
4 and a.statistic# = b.statistic#
5 /

Total maximam memory for all sessions: 183782376 bytes

Thanks,

Kuldeep