 |
|
|
Beginning with 8i, Oracle began to introduce many new features that helped DBAs plan and manage their storage structures in a more efficient manner. Topping the list are locally-managed tablespaces that first appeared in Oracle8i and are now the recommended practice for storage management in Oracle9i. The other form of tablespace extent management, dictionary-managed tablespaces, had been the norm in Oracle until 8i came along.
In a locally-managed tablespace, space management tasks are handled by bitmaps stored within the tablespace itself. A bitmap is used to keep track of the block status in each datafile, whether they are free or used. Each bit in the bitmap maps to a block or a group of blocks in the datafile.
When extents are allocated or released (marked free), Oracle modifies the bitmap values to show the new status of each block. Part of the good news is that these changes do not generate rollback information because they do not update the system tables in the data dictionary, with the rare exception of cases such as tablespace quota updates. The above is an excerpt from Oracle Performance Troubleshooting by Robin Schumacher. It's only $19.95 and you can order it and get instant access to the Oracle scripts here: http://www.rampant-books.com/book_2003_1_perf.htm
|
|
|
