Oracle - Speed up IMPORT Process

Problem: Slow import

Scenario: Truncate table and import repeatedly

Repeated Truncate and import may slow down the process.

The reason is while importing if we don't mention constraints=N, then everytime we import duplicate constraints are created.For example we assume that table ONE has two constraints, If we truncate table,the constraints are still there. For first time import will be fast.During second time, after truncating,and during import(if we doesn't mention CONSTRAINT=N), again two duplicate constraints are created and slows down the import operation little bit.
Each time the duplicate constraints are created it slows down the import process.

Point to be remembered:If we truncate and import table, mention CONSTRAINTS=N explicitly.

Other considerations:

When importing large amounts of data consider dropping indexes prior to the import to speed up the process and re-creating them once the import is completed