Re: On partitioning

On 2014-09-01 11:59:37 -0400, Tom Lane wrote:
> Greg Stark <stark(at)mit(dot)edu> writes:
> > On Sun, Aug 31, 2014 at 9:03 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> Aside from costing planning time, most likely that would forever prevent
> >> us from pushing some types of intelligence about partitioning into the
> >> executor.
>
> > How would it affect this calculus if there were partitioned indexes
> > which were created on the overall table and guaranteed to exist on
> > each partition that the planner could use -- and then possibly also
> > per-partition indexes that might exist in addition to those?
>
> That doesn't actually fix the planning-time issue at all. Either the
> planner considers each partition individually to create a custom plan
> for it, or it doesn't.

We could have a information about the indexing situation in child
partitions on the toplevel table. I.e. note whether child partitions
have individual indexes. And possibly constraints.

> The "push into executor" idea I was alluding to is that we might invent
> plan constructs like a ModifyTable node that applies to a whole
> inheritance^H^H^Hpartitioning tree and leaves the tuple routing to be
> done at runtime. You're not going to get a plan structure like that
> if the planner is building a separate plan subtree for each partition.

It doesn't sound impossible to evaluate at plan time whether to use
nodes covering several partitions or use a separate subplan for
individual partitions. We're going to need information which partitions
to scan in those nodes anyway.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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