Sizing initial Oracle tablespaces
How you size the initial tablespaces depends in part on what they will store, and in part on how you intend to use the database. Let's go through each tablespace one at a time.
The USERS tablespace is used for user data. If you have a large application, however, that doesn't mean that all your application tables go here. They should not. I use USERS as the default tablespace for application users, and I keep the size very small. For the most part, my users don't create objects of their own anyway, so I don't need much space here. If I ever did need space, I could expand the tablespace by adding datafiles.
The size of your TOOLS tablespace depends on what tools you are using. For example, if you were installing Discoverer 2000, you would look in the manual to see how large a tablespace was required for that application's data, and size TOOLS appropriately. Some DBAs choose not to use TOOLS, and instead create a different tablespace for each so called “tool.” Again, you can always expand this tablespace if you need to.
The TEMP tablespace is used for temporary data, such as the data generated by a large sort process. When you sort a lot of data
that will not all fit in memory, Oracle8 divides it into pieces and sorts each piece. The pieces are stored in the TEMP tablespace, read into memory when it is their turn to be sorted, and then written back to disk again. The size of the TEMP tablespace depends on the amount of data that you plan to be sorting at any one time.
The RBS tablespace contains rollback segments. The size depends on the number of transactions that you have going concurrently and the amount of data that these transactions change. Rollback segments are used to store original copies of altered data in the event that a transaction aborts. In the event that happens, the original data is used to undo (or roll back) the changes.