Re: using custom scan nodes to prototype parallel sequential scan

On 12 November 2014 00:54, Robert Haas <robertmhaas@gmail.com> wrote:
> On Tue, Nov 11, 2014 at 3:29 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
>> * only functions marked as "CONTAINS NO SQL"
>> We don't really know what proisparallel is, but we do know what
>> CONTAINS NO SQL means and can easily check for it.
>> Plus I already have a patch for this, slightly bitrotted.
>
> Interestingly, I have a fairly solid idea of what proisparallel is,
> but I have no clear idea what CONTAINS NO SQL is or why it's relevant.
> I would imagine that srandom() contains no SQL under any reasonable
> definition of what that means, but it ain't parallel-safe.

What is wrong in generating random numbers in parallel?

But I'm sure many volatile functions would be annoying to support, so
CONTAINS NO SQL and STABLE/IMMUTABLE seems OK for the first thing.

-- Simon Riggs                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services