The Large Pool

The Large Pool is an optional component of the SGA, though these days it is so useful to have that I doubt many production databases would not be using one: optional it may be in strict right, but I suspect most DBAs these days consider it functionally compulsory.

Whenever you parallelise an operation in Oracle, communication between the individual parallel slaves requires memory access. That memory is usually grabbed from the Shared Pool if nothing else is available: but if a Large Pool has been configured, it gets taken from that instead. You end up using parallel slaves whenever you do a parallel query, perform an RMAN backup or utilise multiple I/O slaves. Parallel query and multiple I/O slaves are slightly exotic (and cost money), but practically every Oracle database on the planet needs backing up with RMAN -so that means practically every Oracle database on the planet needs a Large Pool.

You can do all of these things without a Large Pool, but doing so means the Shared Pool is stressed. It's busy trying to minimise hard parses, and suddenly great gobbets of memory that it needs to do that job are pinched by a backup job or a parallel query! Not a good outcome, in short... and the existence of a Large Pool would mean that such a conflict never arises.

So let me make it simple for you: if you ever back up your database, you need a Large Pool. That should garner a near 100% response, I would have thought!!