Re: Open issues for HOT patch

"Pavan Deolasee" <pavan.deolasee@gmail.com> writes:
> On 9/18/07, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> In a system with
>> HOT running well, the reasons to vacuum a table will be:
>> 
>> 1. Remove dead index entries.
>> 2. Remove LP_DEAD line pointers.
>> 3. Truncate off no-longer-used end pages.
>> 4. Transfer knowledge about free space into FSM.
>> 
>> Pruning cannot accomplish #1, #2, or #3, and without significant changes
>> in the FSM infrastructure it has no hope about #4 either.

> I guess we already have mechanism to remove dead index entries
> outside vacuum.

Not a trustworthy one --- unless you have a solid proposal for making it
work with bitmap indexscans, it would be foolish to design autovacuum
behavior on the assumption that dead index entries aren't a problem.

(Also, IIRC only btree has been taught to recover dead entries at all.)
        regards, tom lane