Re: Viewing the hidden _{Parameters}

I did a check using your query and my _db_block_hash_buckets = 72000 which = 2*db_block_buffers = 36000
not the next prime of 72000
which is 72019

I am running 8.1.7.0 on Sun
I heard there is a patch release to bring me up to 8.1.7.1

"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message news:992619719.9042.0.nnrp-10.9e984b29_at_news.demon.co.uk...
>
> The whole strategy for hash buckets and hash latches
> has changed quite recently, so it is quite possible
> that even Oracle's own consultants haven't caught
> up with it.
>
> It is __possible__ that the number of hash buckets
> is not generated as next_prime(2 x buffers), but
> a recent buffer dump on my 8.1.7 Nt system with
> 1024 buffers showed me 2053 hash chains, which
> happens to be next_prime(2 x 1024). Similarly on
> another 8.1.7 system with 5120 buffers I got 10,243
> chains, which also matches the requirement.
>
> Interestingly the number of hash latches for the
> smaller system was 256 (buffers/4) whereas the
> latch count for the larger system was 1024 (buffers/5).
> I haven't attempted to reverse engineer a formula
> for latches yet.
>
> (PS - to do the dump to see the hash buckets:
>
> alter system set events
> 'immediate trace name buffers level 4';
>
> The dump will be about 700 bytes per buffer.
>
> (Don't do a level 10 dump).
>
>
>
> Look up _kgl_latch_count on Steve Adam's site,
> (http://www.ixora.com.au) I think he has some good
> information on what it is and how it works (but I don't
> think it has anything to do with your problem).
>
>
> In your case, I would drill down to v$latch_children
> to see if any of the cache buffers chains latches
> has an anomalous number of misses, then join
> the relevant v$latch_children.addr with x$bh.hladdr
> to find the ojecet number, file and block addresss
> of the few problem blocks.
>
>
> --
> Jonathan Lewis
> Yet another Oracle-related web site: http://www.jlcomp.demon.co.uk
>
> Practical Oracle 8i: Building Efficient Databases
> Publishers: Addison-Wesley
>
> Reviews at: http://www.jlcomp.demon.co.uk/book_rev.html
>
>
>
> Rob K wrote in message ...
> >We are having a problem with parallel query and latch waits.
> >
> >This is from statspack while running a parallel query.
> >
> >
> > Get Pct Get Avg Slps No Wait
> > req Miss /Miss REq
> >parallel query alloc buffer 844 12.7 0.0 0
> >parallel query stats 58 37.9 0.2 0
> >
> > Get
> >Spin & Sleep
> > req Misses Sleeps 1->4
> >cache buffers chains 11,295,272 805,333 1,647 803775/1474/
> >
> >
> >I was told the oracle DID NOT set the _db_block_hash_buckets to
> >next prime number higher than 2 x DB_BLOCK_BUFFERS
> >
> >that it only sets it to 2 x DB_BLOCK_BUFFERS
> >
> >I was also suggested to set
> >_KGL_LATCH_COUNT - Set to next prime number higher than 2 x CPUs
> >
>
>
>
>
Received on Fri Jun 15 2001 - 10:59:02 CDT