Horton

Re: Parallel execution and prepared statements

Tom Lane <tgl@sss.pgh.pa.us>

View thread
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Albe Laurenz <laurenz.albe@wien.gv.at>, "Tobias Bussmann *EXTERN*" <t.bussmann@gmx.net>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, Amit Kapila <amit.kapila16@gmail.com>
Date: 2016-12-06T18:07:58Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Enable parallelism for prepared statements and extended query protocol.

Robert Haas <robertmhaas@gmail.com> writes:
> Done.

The comment seems quite confused now:

    * If a tuple count was supplied or data is being written to relation, we
    * must force the plan to run without parallelism, because we might exit
    * early.

Exit early is exactly what we *won't* do if writing to an INTO rel, so
I think this will confuse future readers.  I think it should be more like

    * If a tuple count was supplied, we must force the plan to run without
    * parallelism, because we might exit early.  Also disable parallelism
    * when writing into a relation, because [ uh, why exactly? ]

Considering that the writing would happen at top level of the executor,
and hence in the parent process, it's not actually clear to me why the
second restriction is there at all: can't we write tuples to a rel even
though they came from a parallel worker?  In any case, the current wording
of the comment is a complete fail at explaining this.

			regards, tom lane