Re: PGA usage

You could explain the query and see how the database (probably) is
processing this query, and use a 10046/8 trace to see what the session is
doing on execution time.

PGA memory allocated for sort or hash is limited and will go to the
temporary tablespace.

In the ORA-4030 error message is displayed what kind of allocation is done.

frits

On 7/10/07, Yavor Ivanov <Yavor_Ivanov@xxxxxxxx> wrote:



        Hello, frits

        Yes, the /3GB switch is set. And I am using the folowing query to
identify who is eating the PGA:
select sysdate q_time, s.sid, n.name, s.value
from v$statname n, v$sesstat s
where n.statistic# = s.statistic#
and n.name in ('session pga memory')
order by 4 desc, 2;

        The report is just one nasty query, which joins lots of tables and
calls some very basic pl/sql functions about a gazillion times - no arrays,
no cursors, nothing special. Just big sorts and lots of hash joins in the
plan, and basically everything you can think of when you think about
nightmare execution plans. And no hints, by the way.
        But, even if it will be much slower, I just can't understand why
is all this happening in memory and not in TEMP. This leads to whole
database instability - any session can get ora-4030 during the report, when
the memory reaches 3 GB.

--
Regards,
Yavor Ivanov
Senior Database Expert
Stemo Ltd

On Tue, 10 Jul 2007 17:14:57 +0300, Frits Hoogland <
frits.hoogland@xxxxxxxxx> wrote:

> Yavor,
>
> I assume the /3GB switch is set (otherwise the memory available in
userspace
> is limited to 2GB)
>
> The PGA memory can be monitored per session using v$sesstat. Can you
> elaborate on what the report is actually doing? (I suspect a pl/sql
table is
> populated, which is kept in the PGA and doesn't get to the assigned
> temporary tablespace like sort data or hash data.)
>
> AFAIK, the amount of PGA memory which can be allocated by a session is
only
> limited to operating system imposed limits.
>
> frits
>
> On 7/10/07, Yavor Ivanov <Yavor_Ivanov@xxxxxxxx> wrote:
>>
>>         Hello, gurus
>>
>>         I have some problems with Oracle 10.2.0.3 on Windows 2003
32-bit.
>> We have PGA_AGGREGATE_TARGET set to 350 MB and a SGA of 2200 MB. Some
of the
>> sessions are shared server ones (which take memory from the large
pool), and
>> others are dedicated. Sometimes, when some big-fat report is running,
the
>> actual PGA allocated grows up to 550 MB and more. Then we are getting
>> ora-4030, because we hit the 3 GB limit of 32 bit windows.
>>         In this cases I can see that one dedicated connection (the one
>> running the big report) has allocated up to 280 MB PGA (this is, one
>> session!). We are not using parallel things, if it matters at all.
>>         I know PGA_AGGREGATE_TARGET is just a target, not a limit. But
I
>> wonder is there any way to limit how much PGA can a single session
consume.
>> I thought there is a rule stating no session can eat more than 10% than
the
>> total target, but this proved to be wrong.
>>
>> --
>> Regards,
>> Yavor Ivanov
>> Senior Database Expert
>> Stemo Ltd
>> --
>> http://www.freelists.org/webpage/oracle-l
>>
>>
>>
>

Other related posts: