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 - 11:34:32 CDT
