Essay: Elimination of Fragmentation
Fragmentation comes about when there is a gap between the disk blocks in a given table. Database layout requires the any objects and tables to be stored in disk blocks which have no gaps (continuous blocks) (Sassen, 2000). More existence of the gaps implies more fragmentation. Fragmentation increases the time taken in database performance operations since it causes more head movements. Head movements are measured in seeks, each seek taking about five milliseconds. Basically, the disk head from one disk track to another is what we call seeks.
According to Schweitzer (1999), Fragmentation can be prevented by setting the initial and the next parameters of the clause storage (which is a Data Definition SQL statement clause). The clause storage forms part of the extent specs. The number of disk blocks allocated originally to a database object is represented by the initial parameter value. The next parameter is representative of the size in disk blocks of the extent that the object will increase by when it needs some more space. Basically, an extent refers to a logical database storage unit made up of continuous disk blocks. Less fragmentation is realized when new extents are added to the database less often. Big initial and next extent sizes are far better than small sizes so long as the disk space is not wasted.
In case there is an existing fragmentation, modification on the next clause in the Alter cluster, Alter table, Alter index and Alter table space DDL SQL statements so as to prevent it from worsening. So as to eliminate an existing fragmentation in a system, database can be exported first the imported. Rebuilding of the database in a separate space and putting it online using a switchover mechanism need to be done if it is in use 24 hours a day everyday (Connolly and Carolyn, 2002).