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RE: 9i - Dynamic SGA - SGA_MAX_SIZE

From: Mladen Gogala <mladen_at_wangtrading.com>
Date: Tue, 05 Aug 2003 08:49:23 -0800
Message-ID: <F001.005C90A9.20030805084923@fatcity.com>


To continue down the Stephen's path, "shutdown abort" will complete very quickly
and will drastically decrease the size of SGA. What is more, the "very busy environment"
Will not be very busy any more. Perhaps very loud, but not very busy.

--
Mladen Gogala
Oracle DBA 



-----Original Message-----
Kirtikumar Deshpande
Sent: Tuesday, August 05, 2003 12:35 PM
To: Multiple recipients of list ORACLE-L


U R Welcome.
Although, reducing SGA size is technically possible, it can be a very
expensive operation in a busy environemt and can take a long time to
complete. I have not run any specific tests to see how long it takes to
reduce SGA by a certain amount, but you can imagine what must be done (find
least used blocks/age out blocks, keep them from re-use, and finally
'detach' them etc..) 

- Kirti  

--- Mohammed Shakir <mshakir08816_at_yahoo.com> wrote:

> Kirti
>
> Thanks for the info.
>
> I could not raise dynamically the size of db_cache_size and did not
> know why, until I noticed the new parameter sga_max_size. Anyway, I
> tried to lower the size of db_cache_size dynamically and I did not
> have a problem. So sgma_max_size does play its role in
> db_cache_sizing.
>
> I have not tested where I increase the size of sga_max_size using
> init.ora and then try to increase the size of db_cache_size
> dynamically by the same size as the increase in sga_max_size. That is
> the test for coming weekend.
>
>
> --- Kirtikumar Deshpande <kirtikumar_deshpande_at_yahoo.com> wrote:
> > SGA_MAX_SIZE was introduced in 9i to allow dynamic sizing of SGA
> > (Dynamic Sizing feature) components such as, shared pool, large
> > pool, buffer cache etc. In versions up to 8i, such changes
> > required bouncing the instance.
> > This parameter assumes the value of the SGA at instance startup.
> > Various components of the SGA can
> > then be increased/reduced as and when needed. The total SGA, thus,
> > can reach a maximum value set
> > by SGA_MAX_SIZE (if set in the init.ora file). That's the idea.
> > However, the implementation is
> > different on various platforms. With ISM, and DISM, on Solaris, there
> > are other issues when it
> > comes to using Dynamic SGA. You may want to search Metalink for
> > specific notes/articles for
> > Solaris.
> > On AIX 5L as I found out, Oracle uses SGA_MAX_SIZE, if set in
> > init.ora, at the instanace startup,
> > and allocates the excess (difference in computed SGA value and set
> > SGA_MAX_SIZE) to 'variable
> > size'. Hence there is no room for any dynamic sizing (upward) of any
> > SGA component. I did not try
> > to downsize shared pool first, and 'upsize' buffer cache later. May
> > be that would work, but that
> > is not the intention of using this parameter.
> >
> > PGA_AGRREGATE_TARGET is completely different from this parameter. It
> > sets an instance-wide upper limit for the memory used by sorting,
> > hashing processes.
> >
> > Hope this helps..
> >
> > - Kirti
> >
> >
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Received on Tue Aug 05 2003 - 11:49:23 CDT

Original text of this message

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