SQLDeveloper using over 100MB of PGA

Question

Perhaps this is normal, but in my Oracle 11g database I am seeing programmers using Oracle's SQL Developer regularly consume more than 100MB of combined UGA and PGA memory. I'd like to know if this is normal and what can be done about it. Our database is on the 32 bit version of Windows 2008, so memory limitations are becoming an increasing concern. I am using the following query to show the memory usage:

SELECT e.SID, e.username, e.status, b.PGA_MEMORY
FROM v$session e
LEFT JOIN 
   (select y.SID, y.value pga, 
      TO_CHAR(ROUND(y.value/1024/1024),99999999) || ' MB' PGA_MEMORY 
   from v$sesstat y, v$statname z 
   where y.STATISTIC# = z.STATISTIC# and NAME = 'session pga memory') b
ON e.sid=b.sid
WHERE (PGA)/1024/1024 > 20
ORDER BY 4 DESC;

It seems that the resource usage goes up any time a table is opened in SQLDeveloper, but even when it is closed the memory does not go away. The problem is worse if the table is sorted while it was open as that seems to use even more memory. I understand how this would use memory while it is sorting, and perhaps even while it is still open, but to use memory after it is closed seems wrong to me. Can anyone confirm this?

Update: I discovered that my numbers were off due to not understanding that the UGA is stored in the PGA under dedicated server mode. This makes the numbers lower than they were, but the problem still remains that SQL Developer seems to use excessive PGA.

Answer 1

Perhaps SQL Developer doesn't close the cursors it had opened. So if you run a query which sorts a million rows and SQL Developer fetches only first 20 rows from there, it needs to keep the cursor open should you want to scroll down and fetch more.

So, it needs to keep some of the PGA memory associated with the cursor's sort area still allocated (it's called retained sort area) as long as the cursor is open and hasn't reached EOF (end-of-fetch).

Pick a session and run:

select sql_id,operation_type,actual_mem_used,max_mem_used,tempseg_size
from v$sql_workarea_active
where sid = &SID_OF_INTEREST

This should show whether some cursors are still kept open with their memory...

Answer 2

Are you using Automatic Memory Management? If yes, I would not worry about the PGA memory used.

See docs:

Automatic Memory Management: http://download.oracle.com/docs/cd/B28359_01/server.111/b28310/memory003.htm#ADMIN11011

MEMORY_TARGET: http://download.oracle.com/docs/cd/B28359_01/server.111/b28320/initparams133.htm

Is there a reason you are using 32 bit Oracle? Most recent hardware supports 64 bit.

Answer 3

Oracle, especially with AMM, will use every bit of memory on the machine you give it. If it doesn't have a reason to de-allocate memory it will not do so. It is the same with storage space: if you delete 20 GB of user data that space is not returned to the OS. Oracle will hold on to it unless you explicitly compact the tablespaces.

I believe a simple test should relieve your concerns. If it's 32 bit, and each SQL Developer session is using 100MB+ of RAM, then you'd only need a few hundred sessions open to cause a low-memory problem...if there really is one.