Re: [HACKERS] Removing [Merge]Append nodes which contain a single subpath

On 26 October 2017 at 23:30, Robert Haas <robertmhaas@gmail.com> wrote:
> On Wed, Oct 25, 2017 at 11:59 PM, David Rowley
> <david.rowley@2ndquadrant.com> wrote:
>> As of today, because we include this needless [Merge]Append node, we
>> cannot parallelise scans below the Append.
>
> Without disputing your general notion that singe-child Append or
> MergeAppend nodes are a pointless waste, how does a such a needless
> node prevent parallelizing scans beneath it?

hmm, I think I was wrong about that now. I had been looking over the
regression test diffs after having made tenk1 a partitioned table with
a single partition containing all the rows, but it looks like I read
the diff backwards. The planner actually parallelized the Append
version, not the non-Append version, like I had previously thought.

-- David Rowley                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services


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