> > I don't think you need to do anything in the path creation code for this.
> > As is it flattens all AppendPath hierarchies whether for partitioning or
> > inheritance or subqueries. We should leave it as it is.
> I thought it would be convenient for pairwise join code to work with the
> hierarchy intact even within the AppendPath tree.  If it turns out to be
> so, maybe that patch can take care of it.

Partition-wise join work with RelOptInfos, so it's fine if the AppendPath
hierarchy is flattened out. We need the RelOptInfo hierarchy though.

> >> I think I can manage to squeeze in (a) in the next version patch and
> will
> >> also start working on (b), mainly the part about RelOptInfo getting some
> >> partitioning info.
> >
> > I am fine with b, where you would include some partitioning information
> in
> > RelOptInfo. But you don't need to do what you said in (b) above.
> >
> > In a private conversation Robert Haas suggested a way slightly different
> > than what my patch for partition-wise join does. He suggested that the
> > partitioning schemes i.e strategy, number of partitions and bounds of the
> > partitioned elations involved in the query should be stored in
> PlannerInfo
> > in the form of a list. Each partitioning scheme is annotated with the
> > relids of the partitioned relations. RelOptInfo of the partitioned
> relation
> > will point to the partitioning scheme in PlannerInfo. Along-with that
> each
> > RelOptInfo will need to store partition keys for corresponding relation.
> > This simplifies matching the partitioning schemes of the joining
> relations.
> > Also it reduces the number of copies of partition bounds floating around
> as
> > we expect that a query will involve multiple partitioned tables following
> > similar partitioning schemes. May be you want to consider this idea while
> > working on (b).
> So IIUC, a partitioned relation's (baserel or joinrel) RelOptInfo has only
> the information about partition keys.  They will be matched with query
> restriction quals pruning away any unneeded partitions which happens
> individually for each such parent baserel (within set_append_rel_size() I
> suppose).  Further, two joining relations are eligible to be considered
> for pairwise joining if they have identical partition keys and query
> equi-join quals match the same.  The resulting joinrel will have the same
> partition key (as either joining relation) and will have as many
> partitions as there are in the intersection of sets of partitions of
> joining rels (intersection proceeds by matching partition bounds).
> "Partition scheme" structs go into a PlannerInfo list member, one
> corresponding to each partitioned relation - baserel or joinrel, right?

Multiple relations (base or join) can share Partition Scheme if they are
partitioned the same way. Each partition scheme also stores the relids of
the base relations partitioned by that scheme.

> As you say, each such struct has the following pieces of information:
> strategy, num_partitions, bounds (and other auxiliary info).  Before
> make_one_rel() starts, the list has one for each partitioned baserel.
After make_one_rel() has formed baserel pathlists and before
> make_rel_from_joinlist() is called, are the partition scheme structs of
> processed baserels marked with some information about the pruning activity
> that occurred so far?

Right now pruned partitions are labelled as dummy rels (empty appent
paths). That's enough to detect a pruned partition. I haven't found a need
to label partitioning scheme with pruned partitions for partition-wise join.

> Then as we build successively higher levels of
> joinrels, new entries will be made for those joinrels for which we added
> pairwise join paths, with relids matching the corresponding joinrels.
> Does that make sense?
I don't think we will make any new partition scheme entry in PlannerInfo
after all the base relations have been considered. Partitionin-wise join
will pick the one suitable for the given join. But in case partition-wise
join needs to make new entries, I will take care of that in my patch.

Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

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