Eliminating interleaved extents

You can eliminate interleaved extents by reorganizing the tables with the UNLOAD and LOAD statements, creating or altering an index to cluster, or using the ALTER TABLE statement.

Reorganizing dbspaces and tables to eliminate extent interleaving
You can rebuild a dbspace to eliminate interleaved extents so that the extents for each table are contiguous.
Creating or altering an index to cluster
Depending on the circumstances, you can eliminate extent interleaving if you create a clustered index or alter a clustered index. When you use the TO CLUSTER clause of the CREATE INDEX or ALTER INDEX statement, the database server sorts and reconstructs the table.
Using ALTER TABLE to eliminate extent interleaving
If you use the ALTER TABLE statement to add or drop a column or to change the data type of a column, the database server copies and reconstructs the table. When the database server reconstructs the entire table, it rewrites the table to other areas of the dbspace. However, if other tables are in the dbspace, no guarantee exists that the new extents will be adjacent to each other.

Parent topic: Monitoring the upper limit on extents and extent interleaving