On Thu, Oct 20, 2016 at 2:50 PM, Pavan Deolasee
<pavan.deola...@gmail.com> wrote:
> Actually, if we could add an API which can truncate FSM to the given heap
> block, then the user may not even need to run VACUUM, which could be costly
> for very large tables.


> Also, AFAICS we will need to backport
> pg_truncate_visibility_map() to older releases because unless the VM is
> truncated along with the FSM, VACUUM may not scan all pages and the FSM for
> those pages won't be recorded.

This would need a careful lookup, and it would not be that complicated
to implement. And this bug justifies the presence of a tool like that
actually... But usually those don't get a backpatch, so the
probability of getting that backported is low IMO, personally I am not
sure I like that either.

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