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Re: db_block_lru_latches

From: Connor McDonald <connor_mcdonald_at_yahoo.com>
Date: Tue, 30 Jul 2002 18:40:38 +0100
Message-ID: <3D46CF96.774E@yahoo.com>


Richard Foote wrote:
>
> Hi Daud,
>
> The key to the number of db_block_lru_latches is to have at least enough
> (govern by the number of buffer pools you have) and enough to reduce
> contention to a minimum (govern by the sleeps to gets for cache buffers lru
> chain statistic in vs.$latch or as documented in statspack).
>
> Having more than necessary means a bit more overhead inspecting all the lru
> chains (and grabbing the necessary latches) when DBWRs especially need to
> compile their write batches and the such. This is unnecessary overhead if
> just the maximum is assigned (which I think BTW has increased since the
> formula you provided).
>
> I would recommend keeping tabs on the contention for these latches and
> assign as many as necessary.
>
> Cheers
>
> Richard
>
> "Daud" <daud11_at_hotmail.com> wrote in message
> news:f0bf3cc3.0207300540.3e88d45_at_posting.google.com...
> > From oracle documentation, it says that using the default value (1??)
> > for db_block_lru_latches may not be good enough especially when # of
> > db writers is set to more than 1. My question is will it be ok to just
> > set it to the maximum which is # of cpu x 2 x 3? Any impact on the
> > performance setting it to the max? The value of db_block_buffers is
> > 100,000.
> >
> > rgds
> > Daud

Interestingly there is a metalink note (182709.1) which basically concedes "we (Oracle) default it to cpu/2 but we really should make it cpu*2"...

They don't justify the statement - interestingly on my 9i2 instance (on a lowly laptop), "_db_block_lru_latches" pops out at 8!

Cheers
Connor

-- 
==============================
Connor McDonald

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."
Received on Tue Jul 30 2002 - 12:40:38 CDT

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