Re: Parallel Append can break run-time partition pruning

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: David Rowley <dgrowleyml(at)gmail(dot)com>
Cc: Amit Langote <amitlangote09(at)gmail(dot)com>, Robert Haas <robert(dot)haas(at)enterprisedb(dot)com>, amitdkhan(dot)pg(at)gmail(dot)com, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Parallel Append can break run-time partition pruning
Date: 2020-04-22 23:11:05
Message-ID: 8281.1587597065@sss.pgh.pa.us
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David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> Given the same set of paths, when would a non-parallel append be
> cheaper than a parallel one?

Well, anytime the parallel startup cost is significant, for starters.
But maybe we account for that at some other point, like when building
the Gather?

regards, tom lane

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