On 2021-Mar-23, Robert Haas wrote:
> Likewise, the XXX comment you added to max_parallel_hazard_walker
> claims that some of the code introduced there is to compensate for an
> unspecified bug in the rewriter. I'm a bit skeptical that the comment
> is correct, and there's no way to find out because the comment doesn't
> say what the bug supposedly is, but let's just say for the sake of
> argument that it's true. Well, you *could* have fixed the bug, but
> instead you hacked around it, and in a relatively expensive way that
> affects every query with a CTE in it whether it can benefit from this
> patch or not. That's not a responsible way of maintaining the core
> PostgreSQL code.
I think the CTE bug is this one:
https://www.postgresql.org/message-id/flat/CAJcOf-fAdj=nDKMsRhQzndm-O13NY4dL6xGcEvdX5Xvbbi0V7g@mail.gmail.com
while I can't disagree with the overall conclusion that it seems safer
to revert parallel INSERT/SELECT given the number of alleged problems,
it is true that this bug exists, and has gone unfixed.
--
Álvaro Herrera Valdivia, Chile