Re: Performance Improvement for Unique Indexes

Gokulakannan Somasundaram <gokul007@gmail.com> writes:
>    While i was studying the unique index checks very closely, i realized
> that what we need is to find out whether the tuple is deleted / not. So say
> a tuple is deleted by a transaction, but it is not dead( because of some
> long running transaction ), still we can mark a hint bit as deleted and it
> will help the subsequent transactions doing the unique checks. As a matter
> of fact, it will help the deferred_unique cases, since it will anyway check
> the tuples twice, if there is a duplicate.

It seems fairly unlikely to me that this would be useful enough to
justify using up a precious hint bit.  The applicability of the hint
is very short-term --- as soon as the tuple is dead to all transactions,
it can be marked with the existing LP_DEAD hint bit.  And if it's only
useful for uniqueness checks, as seems to be the case, that's another
big restriction on the value.
        regards, tom lane