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Oracle Tips by Burleson 

Oracle9i and multiple block sizes

The ability of Oracle to support multiple block sizes did not get a lot of fanfare during the publicity rollout of Oracle9i. Rather than being touted as an important tool to reduce disk I/O, the multiple block size feature was buried far down on the list of new features of the Oracle9i database. However, for the Oracle administrator, multiple blocksizes are extremely important and exciting. For the first time, you will be able to customize your data buffer sizes according to the specific needs of your database.

The ability to support multiple block sizes within Oracle9i opens up a whole new world of disk I/O management. Prior to Oracle9i, your entire Oracle database had to have a single block size and this block size was determined at the time that the database was created.

With the introduction of Oracle8i, we received the ability to segregate tables and index blocks into three separate data buffers, but all of the buffer caches had to be the same block size. We had the KEEP pool to store frequently referenced table blocks, the RECYCLE pool to hold blocks from large-table full-table scans, and a DEFAULT pool for miscellaneous object blocks.

With Oracle9i, we can define tablespaces with block sizes of 2K, 4K, 8K, 16K and 32K, and assign tables and indexes to the best block size to minimize I/O and best manage wasted space in our data buffers. When we combine the new data buffers for these block sizes, we get a total of seven separate and distinct data buffers to segregate our incoming table and index rows.

As we know, disk I/O is the single most expensive operation within an Oracle9i database, and multiple block sizes give us a powerful new tool to manage disk I/O with more power than ever before.

The above is an excerpt from the "Oracle9i UNIX Administration Handbook" by Oracle press, authored by Donald K. Burleson.


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