Investigate session PGA for one process

Question

Windows server 2003 with Oracle 9.2.0.8.0
In this server there's a process (myprocess.exe) that runs every night at 4:00.
The process is always running, but only does actually work between 4:00 and 5:00. The rest of the day is present, with doing anything (idle).
Running this query:
SELECT
s.sid sid
, lpad(s.username,12) oracle_username
, lpad(s.osuser,9) os_username
, s.program session_program
, lpad(s.machine,8) session_machine
, (select ss.value/1024/1024 from v$sesstat ss, v$statname sn
where ss.sid = s.sid and
sn.statistic# = ss.statistic# and
sn.name = 'session pga memory') session_pga_memory
, (select ss.value/1024/1024 from v$sesstat ss, v$statname sn
where ss.sid = s.sid and
sn.statistic# = ss.statistic# and
sn.name = 'session pga memory max') session_pga_memory_max
, (select ss.value/1024/1024 from v$sesstat ss, v$statname sn
where ss.sid = s.sid and
sn.statistic# = ss.statistic# and
sn.name = 'session uga memory') session_uga_memory
, (select ss.value/1024/1024 from v$sesstat ss, v$statname sn
where ss.sid = s.sid and
sn.statistic# = ss.statistic# and
sn.name = 'session uga memory max') session_uga_memory_max
FROM
v$session s
ORDER BY session_pga_memory DESCI can see that myprocess.exe has:
154Mb of session_PGA_memory
163Mb of session_pga_memory_max
104Mb of session_UGA_memory
111MB of session_UGA_memory_max
For a idle process, this is just to much. So I think there are a lot of cursors not being close.
If I kill the myprocess.exe, immediaty I can see the oracle.exe memory used drop... around ~150MB.
If I restart myprocess.exe, PGA only has 4MB... until the next morning, where it has ~150Mb.
Getting the SID for myProcess.exe, and running this query:
SELECT s.machine, oc.user_name, oc.sql_text, count(1)  FROM v$open_cursor oc, v$session s
WHERE oc.sid = s.sid
AND s.sid=38
GROUP BY user_name, sql_text, machine
HAVING COUNT(1) > 1 ORDER BY count(1) DESC I was expecting to find a lot of cursors... but I did not! Only 9 rows are returned, and all with similat Sql_Text
"DELETE from GT_A "
"DELETE from GT_B "
"DELETE from GT_C "
(9 rows returned)
This GT_* are 9 global temporay tables, used in the PL/SQL execution.
1) Why are this 9 "DELETE from GT_" still present in open_cursors, if the process is idle since 5:00?
2) Checking the code, I found that they are created with: "On commit delete rows"...
but could this 9 global temporary tables justify the 154MB of PGA not release in the session?
Thanks in advance;
Edited by: PauloSMO on 6/Set/2011 4:20

Answer 1

The fact that the work area policy is set to auto and that you're on dedicated server of course invalidates the setting here. It's just a little odd that it was set given the docs state that it is defaulted to 0 and is recommended to be used in shared server environments.
Oracle does not recommend using the SORT_AREA_RETAINED_SIZE parameter unless the instance is configured with the shared server option. >Oracle recommends that you enable automatic sizing of SQL working areas by setting PGA_AGGREGATE_TARGET instead. >SORT_AREA_RETAINED_SIZE is retained for backward compatibility.
PauloSMO wrote:Still active looking for a way to find why a idle process, has is session with 160MB in PGA.
Why does it not free memory to the Operating System!The pga_aggregate_target is a target. It will be exceded if necessary. If the memory is being used it can't be returned to the OS. The issue is finding out where it is using the memory. As you can see it's not particularly easy to dig into the real detail of what's contained in the PGA for that particular session, so why not set up a simple job to query the stats for that session every 10 seconds or something? That way you'll be able to get a profile of when the memory usage is going up and hopefully be able to correlate that with what the process is doing. It's not ideal but that's essentially what something like active session history is doing. If you have a decent level of instrumentation via things like dbms_application_info, it will make the job a little easier.
HTH
David