Re: Hot Standby (commit fest version - v5)

On Thu, 2008-11-20 at 10:33 -0500, Tom Lane wrote:
> "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com> writes:
> > I wonder if we should refactor lazy_scan_heap() so that *all* the real work
> > of collecting information about dead tuples happens only in
> > heap_page_prune(). Frankly, there is only a rare chance that a tuple may
> > become DEAD after the pruning happened on the page. We can ignore such
> > tuples; they will be vacuumed/pruned in the next cycle.
>
> > This would save us a second check of HeapTupleSatisfiesVacuum on the tuples
> > which are just now checked in heap_page_prune(). In addition, the following
> > additional WAL records are then not necessary because heap_page_prune() must
> > have already logged the latestRemovedXid.
>
> I don't think you can do that. Couldn't someone else have run
> heap_page_prune between vacuum's first and second visit to the page?

I just looked at that in more detail and decided it was more difficult
than it first appeared. So I've left it for now.

--
Simon Riggs www.2ndQuadrant.com
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