Is it recommended practice to use uniform extent sizes in Oracle tablespaces?

Question

I've been using Oracle for quite some time since Oracle 8i was released. I was new to the database at that time and was taught that it was best to use constant sized extent sizes when defining tablespaces.

From what I have read, it seems that today using 10/11g, that Oracle can manage these extent sizes for you automatically and that it may not keep extent sizes constant. I can easily see how this can more efficiently use disk space, but are their downsides to this. I'm thinking it may be time to let go of the past on this one. (assuming my past teaching was correct in the first place)

Answer 1

Yes, except for very unusual cases it's time to let go of the past and use the new Oracle extent management features. Use locally-managed tablespaces (LMT's) and the auto extent sizing and you don't have to think about this stuff again.

As a DBA, the variable extent sizing worried me at first since in the 7.3 days I spent a lot of time reorganizing tablespaces to eliminate the fragmentation that resulted from extent allocation with non-zero percent increases. (and you needed non-zero percent increases because your maximum number of extents was capped at different levels depending on the database block size used when you created the database) However, Oracle uses an algorithm to determine the rate and magnititude of extent size increases that effectively eliminates fragmentation.

Also, forget anything you have heard about how the optimum configuration is to have a table or index fit into a single extent or that you can somehow manage i/o through extent configuration - this has never been true. In the days of dictionary-managed tablespace there was probably some penalty to having thousands of extents managed in a dictionary table, but LMT's use bitmaps and this is not an issue. Oracle buffers blocks, not segment extents.