Re: Custom/Foreign-Join-APIs (Re: [v9.5] Custom Plan API)

2015/03/25 18:53、Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com> のメール：

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> On Wed, Mar 25, 2015 at 3:14 PM, Shigeru HANADA <shigeru(dot)hanada(at)gmail(dot)com> wrote:
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> Or bottom of make_join_rel(). IMO build_join_rel() is responsible for just building (or searching from a list) a RelOptInfo for given relids. After that make_join_rel() calls add_paths_to_joinrel() with appropriate arguments per join type to generate actual Paths implements the join. make_join_rel() is called only once for particular relid combination, and there SpecialJoinInfo and restrictlist (conditions specified in JOIN-ON and WHERE), so it seems promising for FDW cases.
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> I like that idea, but I think we will have complex hook signature, it won't remain as simple as hook (root, joinrel).

Signature of the hook (or the FDW API handler) would be like this:

typedef void (*GetForeignJoinPaths_function ) (PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
JoinType jointype,
SpecialJoinInfo *sjinfo,
List *restrictlist);

This is very similar to add_paths_to_joinrel(), but lacks semifactors and extra_lateral_rels. semifactors can be obtained with compute_semi_anti_join_factors(), and extra_lateral_rels can be constructed from root->placeholder_list as add_paths_to_joinrel() does.

From the viewpoint of postgres_fdw, jointype and restrictlist is necessary to generate SELECT statement, so it would require most work done in make_join_rel again if the signature was hook(root, joinrel). sjinfo will be necessary for supporting SEMI/ANTI joins, but currently it is not in the scope of postgres_fdw.

I guess that other FDWs require at least jointype and restrictlist.

—
Shigeru HANADA