Re: Poor Buffer Hit Ratio

<junderhi_at_my-deja.com> schreef in berichtnieuws 8eph7l$6tt$1_at_nnrp1.deja.com...
> We are running Oracle 8.0.4 on an 8-way R50 with 1GB of physical memory.
 The
> machine is running 4 instances with the largest approximately 30GB in
 total
> size. This largest instance is using db_block_size of 4096 and has 120000
> db_block_buffers. The instance previously had only 40000
 db_block_buffers,
> but after noticing our block buffer hit ratio of approx 70%, I tripled it.
> Unfortunately, we have not obvered a performance increase as the hit ratio
 is
> still 70%. We are considering doubling the physical memory, but I'm not
> convinced that this low hit ratio will be alleviated with a generic
 increase
> in physical memory. Any suggestions?
>
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.

Frankly, you should be amazed it still works at all. Running 4 instances on one single server with only 1 G of memory is a proof of either - insufficient funding by management
- someone has gone insane
(Sorry for such blunt words).
Oracle recommends using not more than one third of memory for SGA, you should be way beyond that and observe heavy pagefaulting on the server. Buy that memory, or better still buy that second server (they're not that expensive!!!!).
To determine an increase in hit ratio other than to stick a thumb in the air,
set db_block_lru_statistics (init.ora parameter) to the amount you want to add (in number of buffers), bounce the database and observe the results in the x$kcbrbh table.

Hth,

Sybrand Bakker, Oracle DBA Received on Wed May 03 2000 - 00:00:00 CDT