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Ensure that foreign scans with lateral refs are planned correctly.

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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 bbcafabb44
commit e3101a0317
6 changed files with 131 additions and 5 deletions
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18
contrib/postgres_fdw/postgres_fdw.c
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@ -897,6 +897,9 @@ postgresGetForeignPaths(PlannerInfo *root,
* baserestrict conditions we were able to send to remote, there might
* actually be an indexscan happening there). We already did all the work
* to estimate cost and size of this path.
*
* Although this path uses no join clauses, it could still have required
* parameterization due to LATERAL refs in its tlist.
*/
path = create_foreignscan_path(root, baserel,
NULL, /* default pathtarget */
@ -904,7 +907,7 @@ postgresGetForeignPaths(PlannerInfo *root,
fpinfo->startup_cost,
fpinfo->total_cost,
NIL, /* no pathkeys */
NULL, /* no outer rel either */
baserel->lateral_relids,
NULL, /* no extra plan */
NIL); /* no fdw_private list */
add_path(baserel, (Path *) path);
@ -4374,7 +4377,7 @@ add_paths_with_pathkeys_for_rel(PlannerInfo *root, RelOptInfo *rel,
startup_cost,
total_cost,
useful_pathkeys,
NULL,
rel->lateral_relids,
sorted_epq_path,
NIL));
}
@ -4511,6 +4514,13 @@ postgresGetForeignJoinPaths(PlannerInfo *root,
if (joinrel->fdw_private)
return;
/*
* This code does not work for joins with lateral references, since those
* must have parameterized paths, which we don't generate yet.
*/
if (!bms_is_empty(joinrel->lateral_relids))
return;
/*
* Create unfinished PgFdwRelationInfo entry which is used to indicate
* that the join relation is already considered, so that we won't waste
@ -4602,7 +4612,7 @@ postgresGetForeignJoinPaths(PlannerInfo *root,
startup_cost,
total_cost,
NIL, /* no pathkeys */
NULL, /* no required_outer */
joinrel->lateral_relids,
epq_path,
NIL); /* no fdw_private */
@ -4921,7 +4931,7 @@ add_foreign_grouping_paths(PlannerInfo *root, RelOptInfo *input_rel,
startup_cost,
total_cost,
NIL, /* no pathkeys */
NULL, /* no required_outer */
grouped_rel->lateral_relids,
NULL,
NIL); /* no fdw_private */