On Tue, Jan 23, 2007 at 01:48:08PM +0530, Pavan Deolasee wrote:
> We might not be able to reuse the line pointers because indexes may have > references to it. All such line pointers will be freed when the page is > vacuumed during the regular vacuum.
The overwhelming vast majoirty of tuples are going to be in one or more indexes. Which means nearly all tuples are going to fall into this category. So where's the benefit?
The line pointers can not reused, but the space consumed by the tuple can be. So the benefit is in utilizing that space for newer tuples and thus reduce the bloat.
One assumption I am making here is that its sufficient to mark the line pointer "unused" (reset LP_USED flag) even though there is an index entry pointing to the tuple. During index scan, we anyways check for ItemIdIsUsed() before proceeding further. I know it might break the ctid chain, but does that really matter ? I don't see any reason why somebody would need to follow ctid chain past a dead tuple.