Bruce Momjian wrote:
> On Thu, Feb 23, 2017 at 03:45:24PM -0300, Alvaro Herrera wrote:

> > > and potentially trim the first HOT chain as those tuples become
> > > invisible.
> > 
> > That can already happen even without WARM, no?
> Uh, the point is that with WARM those four early tuples can be removed
> via a prune, rather than requiring a VACUUM. Without WARM, the fourth
> tuple can't be removed until the index is cleared by VACUUM.

I *think* that the WARM-updated one cannot be pruned either, because
it's pointed to by at least one index (otherwise it'd have been a HOT
update).  The ones prior to that can be removed either way.

I think the part you want (be able to prune the WARM updated tuple) is
part of what Pavan calls "turning the WARM chain into a HOT chain", so
not part of the initial patch.  Pavan can explain this part better, and
also set me straight in case I'm wrong in the above :-)

Álvaro Herrera      
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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