Re: Parallell Optimizer

On Tue, Jun 11, 2013 at 9:45 AM, Tatsuo Ishii <ishii(at)postgresql(dot)org> wrote:

> > On Sat, Jun 8, 2013 at 5:04 AM, Simon Riggs <simon(at)2ndquadrant(dot)com>
> wrote:
> >
> >> On 7 June 2013 20:23, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >>
> >> > As for other databases, I suspect that ones that have parallel
> execution
> >> > are probably doing it with a thread model not a process model.
> >>
> >> Separate processes are more common because it covers the general case
> >> where query execution is spread across multiple nodes. Threads don't
> >> work across nodes and parallel queries predate (working) threading
> >> models.
> >>
> > Indeed. Parallelism based on processes would be more convenient for
> > master-master
> > type of applications. Even if no master-master feature is implemented
> > directly in core,
> > at least a parallelism infrastructure based on processes could be used
> for
> > this purpose.
>
> As long as "true" synchronous replication is not implemented in core,
> I am not sure there's a value for parallel execution spreading across
> multile nodes because of the delay of data update propagation.
>
True, but we cannot drop the possibility to have such features in the future
either, so a process-based model is safer regarding the possible range of
features and applications we could gain with.
--
Michael