Unusable Indexes

In this part of the series I'll cover some basics about data loading:

1. If you want to load a large amount of data quickly into a table or partition that gets truncated before the load and indexes also need to be maintained, then it is probably faster to set the the indexes to unusable before the load and rebuild them afterwards instead of letting the insert maintain the indexes. Note that even with a direct-path insert the index maintenance of usable indexes will generate undo and redo, whereas a separate index rebuild doesn't generate undo and can be also be run as a nologging operation if desired. However, as always, test for your particular situation/configuration as the index maintenance as part of direct-path inserts are quite efficient and therefore might not be that much slower than separate index rebuild steps.

In my previous post, I discussed how Oracle from 11g R2 onwards will automatically drop the segment and associated storage from unusable index objects. Mohamend Houri asked in the comments section the excellent question of just how useful this feature will be in real life cases when typically indexes are not left in an unusuable state for a [...]

Following on from my previous discussion on “Create On Demand” segments, Oracle 11g R2 has also introduced storage saving initiatives in relation to useable indexes.  Starting with a simple Oracle 10g example, we create a table and associated index:        If we now make the index unusable:        We notice that [...]