Re: Parallel Seq Scan

On Fri, Feb 6, 2015 at 2:13 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> My first comment here is that I think we should actually teach
> heapam.c about parallelism.

I coded this up; see attached.  I'm also attaching an updated version
of the parallel count code revised to use this API.  It's now called
"parallel_count" rather than "parallel_dummy" and I removed some
stupid stuff from it.  I'm curious to see what other people think, but
this seems much cleaner to me.  With the old approach, the
parallel-count code was duplicating some of the guts of heapam.c and
dropping the rest on the floor; now it just asks for a parallel scan
and away it goes.  Similarly, if your parallel-seqscan patch wanted to
scan block-by-block rather than splitting the relation into equal
parts, or if it wanted to participate in the synchronized-seqcan
stuff, there was no clean way to do that.  With this approach, those
decisions are - as they quite properly should be - isolated within
heapam.c, rather than creeping into the executor.

(These patches should be applied over parallel-mode-v4.patch.)

--
Robert Haas
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