Robert Haas wrote:
> On Fri, Jul 31, 2015 at 2:21 PM, Alvaro Herrera
> <alvherre@2ndquadrant.com> wrote:
> > I think the only way to produce usable estimates is to report more than
> > one number. And in the particular case of lazy vacuuming, ISTM the way
> > to do it is to consider heap scanning as one phase, index cleanup as
> > another phase; these two phases can be interleaved. And there's a final
> > heap scan which is a third phase, which can only run after phases one
> > and two are complete.
>
> That's not really right. There's a phase three for each phase two.
>
> Put in terms of the code, what we're calling phase one is
> lazy_scan_heap(), which prunes all pages, sets hint bits, collects
> dead TIDs, and maybe marks the page all-visible.
>
> When lazy_scan_heap() fills up maintenance_work_mem, or when it
> reaches the end of the heap, it does phase two, which is
> lazy_vacuum_index(), and phase three, which is lazy_vacuum_heap().
> Phase one - lazy_scan_heap() - then keeps going from where it left
> off.
Hmm, you're right. I don't think it changes the essence of what I
suggest, though.
--
Álvaro Herrera http://www.2ndQuadrant.com/
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