RE: speeding up planning with partitions

Amit-san,

On Wed, Mar 6, 2019 at 5:38 AM, Amit Langote wrote:
> On 2019/03/06 11:09, Imai, Yoshikazu wrote:
> > [0004 or 0005]
> > There are redundant process in add_appendrel_other_rels (or
> expand_xxx_rtentry()?).
> > I modified add_appendrel_other_rels like below and it actually worked.
> >
> >
> > add_appendrel_other_rels(PlannerInfo *root, RangeTblEntry *rte, Index
> > rti) {
> > ListCell *l;
> > RelOptInfo *rel;
> >
> > /*
> > * Add inheritance children to the query if not already done. For
> child
> > * tables that are themselves partitioned, their children will be
> added
> > * recursively.
> > */
> > if (rte->rtekind == RTE_RELATION
> && !root->contains_inherit_children)
> > {
> > expand_inherited_rtentry(root, rte, rti);
> > return;
> > }
> >
> > rel = find_base_rel(root, rti);
> >
> > foreach(l, root->append_rel_list)
> > {
> > AppendRelInfo *appinfo = lfirst(l);
> > Index childRTindex = appinfo->child_relid;
> > RangeTblEntry *childrte;
> > RelOptInfo *childrel;
> >
> > if (appinfo->parent_relid != rti)
> > continue;
> >
> > Assert(childRTindex < root->simple_rel_array_size);
> > childrte = root->simple_rte_array[childRTindex];
> > Assert(childrte != NULL);
> > build_simple_rel(root, childRTindex, rel);
> >
> > /* Child may itself be an inherited relation. */
> > if (childrte->inh)
> > add_appendrel_other_rels(root, childrte, childRTindex);
> > }
> > }
>
> If you don't intialize part_rels here, then it will break any code in
> the planner that expects a partitioned rel with non-zero number of
> partitions to have part_rels set to non-NULL. At the moment, that
> includes the code that implements partitioning-specific optimizations
> such partitionwise aggregate and join, run-time pruning etc. No existing
> regression tests cover the cases where source inherited roles
> participates in those optimizations, so you didn't find anything that
> broke. For an example, consider the following update query:
>
> update p set a = p1.a + 1 from p p1 where p1.a = (select 1);
>
> Planner will create a run-time pruning aware Append node for p (aliased
> p1), for which it will need to use the part_rels array. Note that p in
> this case is a source relation which the above code initializes.
>
> Maybe we should add such regression tests.

Ah, now I understand that the codes below of expand_inherited_rtentry() initializes part_rels of child queries after first child target and part_rels of those are used in partitioning-specific optimizations. Thanks for the explanation.

--
Yoshikazu Imai