WHEN TO USE LOGGER IN CREATE INDEX?

Question

HI ALL,
WHEN TO USE LOGGER IN CREATE INDEX STATEMENT? AND WHEN TO USE NOLOGGING?
HOW IS INDEX PHYSICALLY STORED IN DATABASE?
THANKS IN ADVANCE.
SANDESH

Answer 1

NOLOGGING means that information is not written into the redo logs (relatively faster than LOGGING). However, this also means that if you need to recover your database, the index cannot be recovered (since the info cannot be found in the redo logs).
Use NOLOGGING if you need the speed (big indexes) and/or you don't care about being able to recover the index (i.e. if it is acceptable if you recreate it manually after possible database recovery). Alternatively, create the index with NOLOGGING, alter the index to LOGGING and backup the database. Only after the successfull backup will the index be recoverable (with that backup, not an older one).
Typically you should use LOGGING rather than NOLOGGING because the overhead of creating the backup/recovery and insecurity on being able to recover (and pressure that goes along with it) is to great. This option will be handy only in rare cases (e.g. when creating staging area tables/indexes in a datawarehouse. They don't need recovery and will therefore speed up when using NOLOGGING).
Hope this helps,
Lennert