Re: DB_BLOCK_BUFFERS --> DB_CACHE_SIZE

"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

-- 
--------------------------------------------
Oracle Insights: www.dizwell.com
--------------------------------------------