Re: wCTE: why not finish sub-updates at the end, not the beginning? - Mailing list pgsql-hackers

From Tom Lane
Subject Re: wCTE: why not finish sub-updates at the end, not the beginning?
Date
Msg-id 21855.1298648817@sss.pgh.pa.us
Whole thread Raw
In response to Re: wCTE: why not finish sub-updates at the end, not the beginning?  ("Kevin Grittner" <Kevin.Grittner@wicourts.gov>)
List pgsql-hackers
"Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Given that we've decided to run the modifying sub-queries all with
>> the same command counter ID, they are logically executing "in
>> parallel".
>> Just run the main plan and let it pull tuples from the CTEs as
>> needed.
> On the face of it, that sounds like it has another benefit you
> didn't mention -- it sounds like it's much more conducive to
> allowing parallel processing, if (when?) we eventually move in that
> direction.  It might even be a good case for an initial, limited
> implementation.

Yeah.  Most of the executor is in principle parallelizable at the
plan-node level (ignoring the obvious and severe implementation
problems with parallelizing *anything* in the backend).  It's not
good for wCTE to be creating a user-visible assumption that certain
things will happen in a predefined order.
        regards, tom lane


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