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Ensure that foreign scans with lateral refs are planned correctly.

As reported in bug #15613 from Srinivasan S A, file_fdw and postgres_fdw
neglected to mark plain baserel foreign paths as parameterized when the
relation has lateral_relids.  Other FDWs have surely copied this mistake,
so rather than just patching those two modules, install a band-aid fix
in create_foreignscan_path to rectify the mistake centrally.

Although the band-aid is enough to fix the visible symptom, correct
the calls in file_fdw and postgres_fdw anyway, so that they are valid
examples for external FDWs.

Also, since the band-aid isn't enough to make this work for parameterized
foreign joins, throw an elog(ERROR) if such a case is passed to
create_foreignscan_path.  This shouldn't pose much of a problem for
existing external FDWs, since it's likely they aren't trying to make such
paths anyway (though some of them may need a defense against joins with
lateral_relids, similar to the one this patch installs into postgres_fdw).

Add some assertions in relnode.c to catch future occurrences of the same
error --- in particular, as backstop against core-code mistakes like the
one fixed by commit bdd9a99aa.

Discussion: https://postgr.es/m/15613-092be1be9576c728@postgresql.org
This commit is contained in:
Tom Lane
2019-02-07 13:10:46 -05:00
parent a29e93e8f9
commit d468da0d65
6 changed files with 132 additions and 4 deletions

View File

@ -521,6 +521,10 @@ fileGetForeignPaths(PlannerInfo *root,
* Create a ForeignPath node and add it as only possible path. We use the
* fdw_private list of the path to carry the convert_selectively option;
* it will be propagated into the fdw_private list of the Plan node.
*
* We don't support pushing join clauses into the quals of this path, but
* it could still have required parameterization due to LATERAL refs in
* its tlist.
*/
add_path(baserel, (Path *)
create_foreignscan_path(root, baserel,
@ -529,7 +533,7 @@ fileGetForeignPaths(PlannerInfo *root,
startup_cost,
total_cost,
NIL, /* no pathkeys */
NULL, /* no outer rel either */
baserel->lateral_relids,
NULL, /* no extra plan */
coptions));