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Re: Maximum Db_cache_size?

From: Jurijs Velikanovs <j.velikanovs_at_gmail.com>
Date: Mon, 19 Jun 2006 12:45:34 +0100
Message-ID: <d6f0def50606190445h5e7e5281k9ec38d873e0c9635@mail.gmail.com>


One case from my previous experience:
I have got a customer who increased (upgraded HW) BUFFER CACHE from 1.5 to 6GB and used (using) KEEP/RECYCLE/DEFAULT pools. With proper apps planing they archived good performance increasing.

It is billing system for telecommunication client. By increasing BC they managed to keep clients' balances as well as client data (extremely active data in billing) in buffer cache. By during that they reduced the load on IO and improved overall performance.
No problems with latches, internal structures etc were reported.

PS It just one example but I am afraid it can't be used as general advise because it application specific considerations were used.

Yury

On 6/19/06, Laimutis Nedzinskas <Laimutis.Nedzinskas_at_landsbanki.is> wrote:
> Thank you for the idea, Steve.
> In my system the advice view shows increasing values only from the current 4GB to 8GB.
> What I am after are *algorithmical* Oracle problems(well, issues) like all kind of hash buckets chains waits, etc. I do not think cache advisor is taking into account those issues.
> At least v$db_cache_advise has no timing column in 9i.
>
>
>
>
>
>
> -----Original Message-----
> From: Steve Perry [mailto:sperry_at_sprynet.com]
> Sent: 19. júní 2006 11:11
> To: Laimutis Nedzinskas
> Subject: Re: Maximum Db_cache_size?
>
> can't you use v$db _cache_advice to tell you the optimal setting for database cache? I think it exists in 9i.
> there are lots of queries on the web to show the point of diminishing returns.
>
>
> On Jun 19, 2006, at 05:54 AM, Laimutis Nedzinskas wrote:
>
> > Just follow up:
> >
> > May be it is somewhat easier to think about the problem in terms of
> > "db buffer cache scalability".
> > Generally the scalability is not linear at the best.
> > Often the scalability graph has a turning point when adding more
> > resources only makes performance worse.
> > The question is what RAM value(or formula) is the turning point for
> > Oracle buffer cache, if any?
> >
> > -----Original Message-----
> > From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-
> > bounce_at_freelists.org] On Behalf Of Laimutis Nedzinskas
> > Sent: 19. júní 2006 10:44
> > To: oracle-l_at_freelists.org
> > Subject: Maximum Db_cache_size?
> >
> > Is it good or bad to use all available (not used for other purposes,
> > eg.
> > shared pool or pga) RAM for buffer cache?
> > I am talking about 32GB RAM range.
> >
> > Oracle is not in-memory database but anyway - memory access is faster
> > than disk access.
> > However I understand that the way(algorithms) Oracle uses RAM may have
> > a practical turning point when adding more RAM will only slow down
> > things.
> >
> > Therefor the question is:
> >
> > - is Oracle(9.2 version) better at utilizing RAM(say, 10-20GB) for
> > buffer cache?
> >
> > - or is it it is better to let file system to utilize this RAM for
> > file cache?
> >
> > - none of the above, stay with moderate RAM usage (few gigabytes for
> > buffer cache) just because buffer cache hit ration is good (98-99%)? I
> > would just like to point out that 1% of disk ("raw") access makes up a
> > considerable response time, may be 50% or so.
> >
> > Thank you in advance,
> > Laimis N.
> >
> > Fyrirvari/Disclaimer
> > http://www.landsbanki.is/disclaimer
> > --
> > http://www.freelists.org/webpage/oracle-l
> >
> >
> > Fyrirvari/Disclaimer
> > http://www.landsbanki.is/disclaimer
> > --
> > http://www.freelists.org/webpage/oracle-l
> >
> >
>
> Fyrirvari/Disclaimer
> http://www.landsbanki.is/disclaimer
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

-- 
Yury
+44 7738 013090 (GMT)
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Received on Mon Jun 19 2006 - 06:45:34 CDT

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