Re: Memory limitations in Oracle?

"Liz Reen" <lizr_at_geologist.com> wrote in message news:MPG.152ad53c25d1f9ea9896df_at_news.supernews.com...
> In article <st91ctos4rkgh8guhce58ev8dfk3te5vql_at_4ax.com>,
> onlyforposting_at_yahoo.com says...
> > Are there any memory limitations in Oracle?
> >
> > In other words, if I have a machine with 20GB of physical memory
> > (hypothetically), can I assign it all to Oracle's SGA via the relevant
> > instance parameters (db_block_buffers, shared_pool_size, log_buffers,
> > etc).
> >
> > On a related note, what is the new large_pool_size parameter in Oracle
> > 8i?
> >

It's not new, it was introduced in 8.0.

It's a new area in the SGA which is used for backup I/O slaves, the UGA in an MTS environment, and DBWR I/O slaves if you're using them. If you don't configure one, but use all these things, they pinch their memory requirements out of the shared pool, and consequently constrict your Library Cache, and hence induce excessive ageing out of shared SQL statements, packages and so on. Performance thus suffers as such things age out, need re-loading, and have to be re-parsed. Accordingly, if you use all (or any of ) these things, much better to reserve a dedicated area of the Large Pool for them to do their stuff in without knackering the Library Cache.

The Large Pool, incidentally, does not have stuff aged out with an LRU list. That's another reason for using one -the things that go into the Large Pool are intrinsically not suited to being aged out. Without a Large Pool, they risk that fate, just like anything else in the Shared Pool. Extremely bad for performance.

Regards
HJR
> > Thanks...
> >
> Do leave some memory for the OS and the users.
>
> Liz
Received on Wed Mar 28 2001 - 02:44:24 CST