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

2015/03/25 18:53、Ashutosh Bapat <ashutosh.bapat@enterprisedb.com> のメール：

>
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> On Wed, Mar 25, 2015 at 3:14 PM, Shigeru HANADA <shigeru.hanada@gmail.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
RelOptInfofor given relids.  After that make_join_rel() calls add_paths_to_joinrel() with appropriate arguments per
jointype 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
promisingfor FDW cases. 
>
> 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
obtainedwith 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
requiremost work done in make_join_rel again if the signature was hook(root, joinrel).  sjinfo will be necessary for
supportingSEMI/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