Re: Allowing join removals for more join types

On Thu, Jun 05, 2014 at 02:12:33AM +0200, Andres Freund wrote:
> On 2014-06-04 20:04:07 -0400, Noah Misch wrote:
> > On Wed, Jun 04, 2014 at 10:14:42AM -0400, Tom Lane wrote:
> > > It's possible that we could apply the optimization only to queries that
> > > have been issued directly by a client, but that seems rather ugly and
> > > surprise-filled.
> >
> > ... such as this idea. It's a good start to a fairly-hard problem. FKs are
> > also always valid when afterTriggers->query_depth == -1, such as when all
> > ongoing queries qualified for EXEC_FLAG_SKIP_TRIGGERS. What else? We could
> > teach trigger.c to efficiently report whether a given table has a queued RI
> > trigger. Having done that, when plancache.c is building a custom plan, the
> > planner could ignore FKs with pending RI checks and use the rest. At that
> > point, the surprises will be reasonably-isolated.
>
> A bit more crazy, but how about trying trying to plan joins with a added
> one-time qual that checks the size of the deferred trigger queue? Then
> we wouldn't even need special case plans.

That, too, sounds promising to investigate.

--
Noah Misch
EnterpriseDB http://www.enterprisedb.com