Re: Performance-improvement idea: shortcircuit unique-index checks

> I'm not quite sure how to implement this, but I wanted to toss the idea
> out for discussion.  Probably we'd have to have some cooperation between
> the heap_update level (where the fact that it's an update is known, and
> where we'd have a chance to test for changes in particular columns) and
> the index access level.  Maybe it's wrong for the index access level to
> have primary responsibility for uniqueness checks in the first place.
> 
> Obviously this isn't going to happen for 7.1, but it might make a nice
> performance improvement for 7.2.

Seems a better solution would be to put a 'deleted' bit in the index so
we would have to visit those heap tuples only once for a committed
status.  Similar to what we do with heap tuples so we don't have to
visit pg_log repeatedly.

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