well, The Operating System Block size is the minimum unit of operation (read /write) by the OS and is a property of the OS file system. While creating an Oracle database we have to choose the 'Data Base Block Size' as a multiple of the Operating System Block size. The minimum unit of operation (read /write) by the Oracle database would be this 'Oracle Block', and not the OS block. Once set, the 'Data Base Block Size' cannot be changed during the life of the database (except in the case of Oracle 9i). To decide on a suitable block size for the database, we take into consideration factors like the size of the database and the concurrent number of transactions expected. Proper block sizing and its use are very important from the tuning point of view.
The availability of the block in the "free list" is determined by the PCTFREE value. Initially, an empty block will be listed in the free list table, and it will continue to remain there until the free space reaches the PCTFREE value. When the free space reaches the PCTFREE value, the block is removed from the free list, and it is re-listed in the free list table when the volume of data in the block comes below the PCTUSED value. Oracle uses the free list to increase the performance. So for every insert operation, Oracle needs to search for the free blocks only from the 'free list' table instead of searching all blocks.
source site: http://www.dbasupport.com/oracle/or a9i/rowchaining.shtml
Answered by
Uttam
, an ibibo Master,
at
9:35 AM on October 22, 2008