Explanation/Reference:
Note:
* You may have noticed that we introduced Invisible Indexes as an 11g New Feature. Their main benefit is that we can test whether performance differs if we would drop an index without actually dropping it. This is particular useful after an Exadata Migration because we expect that some conventional indexes migrated are now obsolete and may be substituted by Storage Indexes.
* With making indexes invisible, we can easily check whether indexes are useful without having to drop (and in case recreate) them actually. While this may be of interest for "ordinary" Oracle Databases already, it is particular a useful feature for Exadata where we expect some conventional indexes to become obsolete after a migration.
* DISABLE NOVALIDATE RELY means: "I don't want an index and constaraint checking to slow down my batch data loading into datawarehouse, but the optimizer can RELY on my data loading routine and assume this constraint is enforced by other mechanism". This information can greatly help optimizer to use correct materialized view when rewriting queries. So if you don't use materialized views for query rewrite then you can put RELY for all your constraints (or NORELY for all your constraits) and forget about it.