Oracle Tables that undergo significant data manipulation (DML) activity, such as UPDATE and DELETE operations, can become fragmented and contain free space “Islands” inside the table seegments.

Such fragmentation reduces the efficiency of scaning opreations like full table scans of index scans. Before oracle 10g one should have used “MOVE TABLE” in order to solve this problem.

Oracle 10g inturduced us with new online feature, shrink table.

In order to use the shrink command we need to enable row movment:

alter table <Table_Name> enable row movement;
--Then we can use shrink table command:
alter table <Table_Name> shrink space;

Shrink opration does the following :

Segment data is compacted
High-water mark (HWM) is adjusted to an appropriate location