Re: Multiple copies of the same block in the buffer cache

Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk> wrote:
>
>There is a parameter named something like
>_max_cr_dba_clone = 6 which limits this,
>as too many clones could result in heavy
>contention on the cache buffers chains
>latch as all clones of a block go into the
>same hash bucket, and the latch has to be
>held whilst the bucket is searched.
>
>Notwithstanding this parameter value, I
>have seen (oracle 8.1.5 I think) up to 12
>copies of a block in the buffer. But this
>isn't something I have seen recently.

Hm... so if your system was suffering cache buffers chains latch contention on root index blocks, and you could see many CR copies in x$bh, might reducing _max_cr_dba_clone be effective tuning?

I suppose one answer is to Just Do It (not on production, don't panic) and see what happens.

-- 
Andrew Mobbs - http://www.chiark.greenend.org.uk/~andrewm/