faster index creation

A good article : http://iggyfernandez.wordpress.com/2011/07/04/take-that-exadata-fast-index-creation-using-noparallel/

Leverage the Oracle cache! This is one case where “direct path reads” and parallelism hurt instead of helping. The trick is to use NOPARALLEL so that data is loaded into shared memory using “db file scattered reads”—instead of being loaded into private memory using direct path reads—and to run multiple CREATE INDEX statements simultaneously. In the words of David Aldridge, you’ll get “get 1 index creation process performing the physical reads and the other 9 (for example) processes greedily waiting for the blocks to load into the buffer.”