Re: speeding up planning with partitions

Thanks for looking.

On 2019/02/19 2:27, Tom Lane wrote:
> Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> writes:
>> [ v22 patch set ]
>
> I started to look at this, and immediately choked on the 0001 patch:
>
> if (childpruned ||
> !apply_child_basequals(root, rel, childrel, childRTE, appinfo) ||
> relation_excluded_by_constraints(root, childrel, childRTE))
> {
>
> Frankly, that code is just horrid. Having a function with side effects
> in an if-test is questionable at the best of times, and having it be
> the second of three conditions (which the third condition silently depends
> on) is unreadable and unmaintainable.
>
> I think the existing code here is considerably cleaner than what this
> patch proposes.

OK, I think we can just skip this patch.

> I suppose you are doing this because you intend to jam some additional
> cleanup code into the successfully-pruned-it code path, but if said
> code is really too bulky to have multiple copies of, couldn't you
> put it into a subroutine?

Actually, one of the later patches (lazy creation of partition RTEs)
*replaces* the the above code block by:

if (IS_DUMMY_REL(childrel))
continue;

because with that patch, the step that prunes/excludes children will occur
earlier than set_rel_size / set_append_rel_size. For pruned children,
there won't RTE/RelOptInfo/AppendRelInfo to begin with. Children that
survive partition pruning but get excluded due to contradictory quals
(apply_child_basequals returning false) or constraint exclusion will be
marked dummy before even getting to set_append_rel_size.

I'll adjust the patches accordingly.

Thanks,
Amit