Why do index access methods use LP_DELETE?

Hi Hackers,

I found index access methods use LP_DELETE for invisible tuples,
but it seems to be ok to remove LP_USED instead of adding LP_DELETE.

I tried the following simple replacements:
- '|= LP_DELETE' => '&= ~LP_USED'
- 'ItemIdDeleted' => '!ItemIdIsUsed'
and then, it passed all regression tests.

Why do index access methods use LP_DELETE?
Does this change make troubles?

(However, I guess there is no advantage in the change,
because unused items are not recycled until next vacuum.)

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ITAGAKI Takahiro
NTT Cyber Space Laboratories