Re: PGA Deallocation

From: Thiago Maciel <thiagomaciel_at_gmail.com>
Date: Mon, 26 Jan 2015 11:06:58 -0300
Message-ID: <CAAHb+wM_wPr+VGVLbtvFQTzWQg-fDWYk-Hu8Mcqqk+oUb_M2jQ_at_mail.gmail.com>

Also, I strongly advise to have a look at the link below:

http://intermediatesql.com/category/aix/

This is an excellent source of information when you want to know more about Oracle running on Aix.

Thiago Maciel

On Thu, Jan 22, 2015 at 6:31 AM, Stefan Koehler <contact_at_soocs.de> wrote:

> Hi Zack,
> yes, that quote is really old and it has changed since 9i. Quoting from
> Tom Kyte's book "Expert Oracle Database Architecture": The PGA is managed
> as a
> heap in 8i releases and is created via malloc()-ed memory. In 9i and
> above, new methods attach and release work areas as needed using operating
> system-specific memory allocation calls.
>
> Realfree heap management was introduced with Oracle 9i (hidden parameter
> "_use_realfree_heap"). You can also crosscheck your PGA usage by using view
> v$sesstat and you will usually see that "session pga memory" / "session
> pga memory max" and respectively "session uga memory" / "session uga memory
> max" differs - especially when using work areas for sorting, hashing, etc..
>
> I assume that you don't have switched from dedicated to shared servers
> along with the app change, right? If your app has changed, it might use some
> new Oracle functions which can cause this memory increase - or some
> functions got a PGA memory leak. The easiest way to find out is dumping the
> PGA
> and analyze the heap dump with Tanel Poder's heapdump_analyzer or use some
> views to a certain point.
>
>
> http://blog.tanelpoder.com/2009/06/24/oracle-memory-troubleshooting-part-3-automatic-top-subheap-dumping-with-heapdump/
>
> http://blog.tanelpoder.com/2014/03/26/oracle-memory-troubleshooting-part-4-drilling-down-into-pga-memory-usage-with-vprocess_memory_detail/
>
> Best Regards
> Stefan Koehler
>
> Freelance Oracle performance consultant and researcher
> Homepage: http://www.soocs.de
> Twitter: _at_OracleSK
>
> > Jack van Zanen <jack_at_vanzanen.com> hat am 22. Januar 2015 um 04:58
> geschrieben:
> >
> > Hi,
> > Long time ago Steve Adams wrote
> >
> > "Although it is technically possible to do so, on most operating
> systems Oracle does not attempt to reduce the size of the process data heap
> > segment and release that virtual memory back to the operating system. So
> from an OS pov, the virtual memory size of an oracle process remains at its
> > high water mark"
> >
> > This was in relation to 8i.
> >
> > We are running AIX 6 and 11G and our sa's have noticed virtual memory
> usage going up.
> >
> > We have had a major app change few months back, so I am just wondering
> if this could be explained as the app is simply doing a lot more processing
> >
> >
> > Jack van Zanen
>
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

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Received on Mon Jan 26 2015 - 15:06:58 CET