Re: Parallel execution and prepared statements

On Fri, Nov 18, 2016 at 8:21 AM, Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at> wrote:
> I didn't notice the CREATE TABLE ... AS EXECUTE problem.
>
> But then the change to use CURSOR_OPT_PARALLEL_OK in tcop/postgres.c should
> be reverted as well, because it breaks things just as bad:
>
> /* creates a parallel-enabled plan */
> PQprepare(conn, "pstmt", "SELECT id FROM l WHERE val = $1", 1, NULL);
> /* blows up with "cannot insert tuples during a parallel operation" */
> PQexec(conn, "CREATE TABLE bad(id) AS EXECUTE pstmt('abcd')");

Ouch. I missed that.

> With Tobias' patch, this does not fail.
>
> I think we should either apply something like that patch or disable parallel
> execution for prepared statements altogether and document that.

I agree. I think probably the first option is better, but I might
have to commit with one hand so I can hold my nose with the other.

--
Robert Haas
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