accessibility vs visibility Oracle SQL -

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my teacher asked me today what's difference between accessibility , visibility in oracle sql points. i'm new this, searched internet didn't found anything. can me? thanks

i searched in oracle database concepts , found 1 match visibility:

indexes have following properties:

■ usability indexes usable (default) or unusable. unusable index not maintained dml operations , ignored optimizer. unusable index can improve performance of bulk loads. instead of dropping index , later re-creating it, can make index unusable , rebuild it. unusable indexes , index partitions not consume space. when make usable index unusable, database drops index segment.

■ visibility indexes visible (default) or invisible. invisible index maintained dml operations , not used default optimizer. making index invisible alternative making unusable or dropping it. invisible indexes useful testing removal of index before dropping or using indexes temporarily without affecting overall application.

this bet. don't know teacher wants.


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