Re: db_block_buffers - can you have too many ?

Hi Richard,

Oracle recommends having about 3 times as much memory as the SGA size, excluding the operating system. We all know how memory hungry Microsoft software is, so 256 Mb is a bit ...
In my previous function I could prove an SGA of 45 Mb was thrashing the OS with the same amount of RAM.
And yes, there will be a point where increasing db_block_buffers doesn't improve the hit rate, and instead starts pushing the OS over the edge. You can measure the efficiency of increasing and decreasing db_block_buffers. Consult the Oracle Server Tuning Guide for details.

Hth,
Sybrand Bakker, Oracle DBA

Richard Anstey wrote:

> Hello,
>
> I'm a newbie here so please go easy on me..
>
> Running O7.3 on NT Intel multiprocessor.
>
> I had sudden performance problems - typical query
> response times up by a factor of 10. No change had been made to the box and
> it's dedicated to Oracle.
>
> The database is quite large - 300 plus tables, and is heavily laden with
> PLSQL code.
>
> With 256MB RAM on the box, I had increased db_block_buffers well above the
> sample values shown in init.ora. (but still keeping the SGA size well below
> total RAM - total SGA size was approx 60MB)
> Oracle support told me to reduce the db_block_buffers and this did actually
> solve the problem !?
>
> Can anyone help me to explain this ? Surely the more database blocks you
> can cached, the better so long as your OS isn't swapping the SGA to disk ?
> Or am I missing something.
>
> Cheers,
>
> Richard.
> ranstey_at_compuserve.com
Received on Tue Nov 10 1998 - 05:40:24 CST