RE: difference between child and parent latches?
- From: K Gopalakrishnan <kaygopal@xxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Tue, 23 Mar 2004 01:39:30 -0800 (PST)
Tanel:
You have hit the nail on its head. _kghdsisx_count defines the number
of sub-pools (or in other words, number of latches for shared pool)
inside the shared pool. This is introduded to have bigger shared pool
sizes without having a latch contention problem. But I have never seen
that working as expected :(
--- Tanel Poder <tanel.poder.003@xxxxxxx> wrote:
> > Not quite true. (at least starting from 9i). The shared pool is
> > divided
> > in to multiple sub-pools if it is greater than 250MB and/or if your
> > cpu_count > 4. In this case the shared pool is covered by multiple
> > shared pool latches.
>
> I use my chance here to throw in an undocumented parameter
> _kghdsidx_count, which you could modify to manually control into how
> many heaps shared pool will be divided.
>
> Each heap has it's own freelist and lru lists and the latch
> protecting operations on them, this means you could relieve shared
> pool latch contention in extremely poorly written applications, but
> also you might introduce unnecessary ORA-4031 problems, when most
> allocations happen to be non-uniformly distributed to some specific
> heap resulting in out of memory error, while others heaps have might
> have enough (but unusable) space in them..
Very true. Recently I had the same problem with shared pool was erring
with 4031 for 2k chunks though the freepsace inside shared pool was
more than 400 MB (the shared pool was set to 1.6G for a 10 thousand
sessions) and the culprit was sub pools. Once we reduced the subpools
lower value from 7, the problem vanished :)
So it is good to have multiple sub pools, but the results may vary :)
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