On Wed, Jul 5, 2017 at 3:19 PM, Peter Geoghegan <pg@bowt.ie> wrote:
> I doubt that myself. Especially prior to Postgres 10, where merging
> will have tuplesort_heap_insert() as the bottleneck.
BTW, I do of course understand that the reporter isn't talking about
merging, but rather is talking about run generation using replacement
selection. Replacement selection is more or less obsolete, and was
more or less removed in Postgres 9.6. I don't think that its needs
should be given much weight here; this is mostly about merging.
I wanted to make merging use its own dedicated function within the
patch that became 24598337c8d, and leave tuplesort_heap_insert() and
tuplesort_heap_siftup() as things used only by replacement selection +
Top-N heap sort, but Heikki overruled me on that. He might have been
right about that. I'm not sure, and never took the time to follow up
with it.
tuplesort_heap_replace_top(), which is where this logic lives now that
tuplesort_heap_siftup() was broken up, certainly is a red-hot code
path where individual instructions could matter. I've looked at the
disassembly of the function in the past, which is rare for me.
--
Peter Geoghegan
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