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From: Tom Lane on 24 Mar 2010 10:39
Gokulakannan Somasundaram <gokul007(a)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

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From: Gokulakannan Somasundaram on 24 Mar 2010 11:34
> 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.
>
> Right. It is of little value.

Gokul.
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