Re: Partition-wise join for join between (declaratively) partitioned tables

On Wed, Sep 13, 2017 at 10:57 PM, Amit Langote
<Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> I very much like pcinfo-for-subquery.patch, although I'm not sure if we
> need to create PartitionedChildRelInfo for the sub-query parent RTE as the
> patch teaches add_paths_to_append_rel() to do. ISTM, nested UNION ALL
> subqueries are flattened way before we get to add_paths_to_append_rel();
> if it could not be flattened, there wouldn't be a call to
> add_paths_to_append_rel() in the first place, because no AppendRelInfos
> would be generated. See what happens when is_simple_union_all_recurse()
> returns false to flatten_simple_union_all() -- no AppendRelInfos will be
> generated and added to root->append_rel_list in that case.
>
> IOW, there won't be nested AppendRelInfos for nested UNION ALL sub-queries
> like we're setting out to build for multi-level partitioned tables.
>
> So, as things stand today, there can at most be one recursive call of
> add_path_to_append_rel() for a sub-query parent RTE, that is, if its child
> sub-queries contain partitioned tables, but not more. The other patch
> (multi-level expansion of partitioned tables) will change that, but even
> then we won't need sub-query's own PartitioendChildRelInfo.

OK, let's assume you're correct unless some contrary evidence emerges.
Committed without that part; thanks for the review.

--
Robert Haas
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