Re: What is the better session memory used stat; UGA or PGA?
- From: "Radoulov, Dimitre" <cichomitiko@xxxxxxxxx>
- To: <cmarquez@xxxxxxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 25 Oct 2005 20:48:22 +0200
What is the better session memory used stat; UGA or PGA?Quote from AskTom
Forum. Try pmap -x.
<quote>
The User Global Area (UGA) is memory that is associated with a user session.
The UGA normally comes from the SGA to allow migration of sessions across
processes. If session migration is disabled, UGA memory will be allocated
from
the PGA.
The Process Global Area (PGA) is memory which is physically private to a
process
(cannot be accessed by another process). Note that an OS process and an
Oracle
session are not equivalent. The PGA, unlike the SGA, can grow at runtime.
So, in dedicated server mode, when session migration is not needed, the UGA
is
in the PGA is in the individual process.
It looks like you are using Solaris. On Solaris, ps, top and other tools
are
virtually useless for looking at memory usage of Oracle processes. They
report back not only the process memory but all shared memory attached by
the
process. You are seeing much of the SGA as well as process memory in that
report.
You should investigate the /usr/proc/bin/pmap utility instead. It'll report
back the breakdown of memory, showing shared memory segments and shared data
from .so files and the like.
</quote>
<quote>
We use UGA memory in dedicated server mode. It is just where is the UGA
located
-- in dedicated server mode, it's in the PGA. In shared server mode, it's
in
the SGA.
If you have my book -- i describe these structures in some detail, here is a
short extract:
...
PGA and UGA
As stated earlier, the PGA is a process piece of memory. This is memory
specific
to a single operating system process or thread. This memory is not
accessible by
any other process/thread in the system. It is typically allocated via the C
run-time call malloc(), and may grow (and shrink even) at run-time. The PGA
is
never allocated out of Oracle's SGA - it is always allocated locally by the
process or thread.
The UGA is in effect, your session's state. It is memory that your session
must
always be able to get to. The location of the UGA is wholly dependent on how
Oracle has been configured to accept connections. If you have configured
MTS,
then the UGA must be stored in a memory structure that everyone has access
to -
and that would be the SGA. In this way, your session can use any one of the
shared servers, since any one of them can read and write your sessions data.
On the other hand, if you are using a dedicated server connection, this need
for universal access to your session state goes away, and the UGA becomes
virtually synonymous with the PGA - it will in fact be contained in the PGA.
In
fact, when you look at the system statistics, you'll find the UGA reported
in
the PGA in dedicated server mode (the PGA will be greater then or equal to
the
UGA memory used, the PGA memory size will include the UGA size as well).
</quote>
For more info:
http://asktom.oracle.com/pls/ask/f?p=4950:8:15452666227313862376::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:267215452482
http://asktom.oracle.com/pls/ask/f?p=4950:8:15452666227313862376::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:404110378143
HTH
Dimitre Radoulov
----- Original Message -----
From: Marquez, Chris
To: oracle-l@xxxxxxxxxxxxx
Sent: Tuesday, October 25, 2005 7:26 PM
Subject: What is the better session memory used stat; UGA or PGA?
ENV;
- 9205
- Dedicated Server Mode.
UGA is part of the PGA, and PGA part of the SGA.
Which is the better stat for session memory (currently) used?
I think and am finding UGA as the answer...but don't want to ignore the
higher PGA number I see, considering what the PGA holds.
SELECT
e.SID,
e.username,
e.status,
a.UGA_MEMORY,
b.PGA_MEMORY
FROM
-- Current UGA size for the session.
(select y.SID, TO_CHAR(ROUND(y.value/1024),99999999) || ' KB'
UGA_MEMORY from v$sesstat y, v$statname z where y.STATISTIC# = z.STATISTIC#
and NAME = 'session uga memory') a,
-- Current PGA size for the session.
(select y.SID, TO_CHAR(ROUND(y.value/1024),99999999) || ' KB'
PGA_MEMORY from v$sesstat y, v$statname z where y.STATISTIC# = z.STATISTIC#
and NAME = 'session pga memory') b,
v$session e
WHERE e.sid=a.sid
AND e.sid=b.sid
ORDER BY
e.status,
a.UGA_MEMORY desc
/
SID USERNAME STATUS UGA_MEMORY
PGA_MEMORY
---------- ------------- ------------------------ -------------------- --------------------
190 SCOTT ACTIVE 14723 KB
17243 KB
25 SYS ACTIVE 2205 KB
401 KB
80 WEBUSERS ACTIVE 422 KB
1616 KB
50 ACTIVE 37 KB
11532 KB
222 ACTIVE 37 KB
8412 KB
169 ACTIVE 37 KB
6370 KB
217 ACTIVE 36 KB
115 KB
16 ACTIVE 36 KB
4255 KB
3 ACTIVE 36 KB
2030 KB
15 ACTIVE 36 KB
4255 KB
19 ACTIVE 36 KB
1366 KB
1 ACTIVE 36 KB
115 KB
11 ACTIVE 35 KB
3443 KB
9 ACTIVE 34 KB
1558 KB
2 ACTIVE 33 KB
208 KB
4 ACTIVE 33 KB
2951 KB
5 ACTIVE 33 KB
3918 KB
10 ACTIVE 33 KB
8439 KB
7 ACTIVE 33 KB
3918 KB
133 WEBUSERS INACTIVE 1653 KB
2546 KB
61 WEBUSERS INACTIVE 1422 KB
2336 KB
194 WEBUSERS INACTIVE 565 KB
1901 KB
154 WEBUSERS INACTIVE 511 KB
1902 KB
22 WEBUSERS INACTIVE 491 KB
1853 KB
Thanks,
Chris Marquez
Oracle DBA
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