Re: DB_BLOCK_BUFFERS --> DB_CACHE_SIZE

very clear explanation
: )

Joe

"Howard J. Rogers" <hjr_at_dizwell.com> wrote in message news:40342623$0$15135$afc38c87_at_news.optusnet.com.au...
>
> "Charles Davis" <cdavis10717_at_comcast.net> wrote in message
> news:87-dnd-4qp3muandRVn-gg_at_comcast.com...
> > All,
> >
> > What is the unit of measure for the value of the Oracle 8i init parm
> > DB_BLOCK_BUFFERS?
>
> Er, the number of buffers. In other words, if you set it to 20000 and your
> db_block_size is 8192, then I know you have a 160M buffer cache.
>
> > I have an Oracle 9i instance that was upgraded from 8i and this init
parm
> is
> > set to 366000.
> >
> > I want to change the init to use DB_CACHE_SIZE instead, which is a clear
> > unit of measure.
>
> And is dynamic, as well (db_block_buffers isn't). And doesn't produce an
> alert message every time you start up.
>
> > I have a block size of 8192, so what do I set the CACHE to for the equal
> > size as the BLOCK_BUFFERS?
>
> My maths is bad: but 366000 x 8192 is 2928000 K, or about 3GB. That's an
> awfully large buffer cache, but presumably you know what you're doing.
>
> Just be warned: if you use the multiple buffer pools feature available
since
> 8.0, then it works completely differently in 9i compared to 8.0 and 8i. In
> 8.0 and 8i, you allocated a total buffer cache (block_buffers x
block_size),
> and then carved bits off that total to give you your other two pools. So
> with block_buffers set to 20000 (ie, 160M), and buffer_pool_keep set to
4000
> (32M) and buffer_pool_recycle set to 6000 (48M), your total buffer cache
> was.... 160M. The two pools come *out* of the total allocated with
> block_buffers.
>
> In 9i, by contrast, db_cache_size only sets the size of the default pool.
If
> you then set db_keep_cache_size and db_recycle_cache_size, those extra
> caches are actually added on: your total buffer cache size becomes the sum
> of all three parameters.
>
> You may not be using the multiple pools feature (and if so, why not?!),
but
> just be wary if you are.
>
> Regards
> HJR
>
>
>
> >
> > many thanks.
> >
> > charles
>
>
>
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>
>
Received on Thu Feb 19 2004 - 03:56:42 CST