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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 8722d2cbc0
commit 9d6d2b2134
6 changed files with 131 additions and 5 deletions
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21
src/backend/optimizer/util/pathnode.c
View File

@ -2069,6 +2069,27 @@ create_foreignscan_path(PlannerInfo *root, RelOptInfo *rel,
{
ForeignPath *pathnode = makeNode(ForeignPath);
/*
* Since the path's required_outer should always include all the rel's
* lateral_relids, forcibly add those if necessary. This is a bit of a
* hack, but up till early 2019 the contrib FDWs failed to ensure that,
* and it's likely that the same error has propagated into many external
* FDWs. Don't risk modifying the passed-in relid set here.
*/
if (rel->lateral_relids && !bms_is_subset(rel->lateral_relids,
required_outer))
required_outer = bms_union(required_outer, rel->lateral_relids);
/*
* Although this function is only designed to be used for scans of
* baserels, before v12 postgres_fdw abused it to make paths for join and
* upper rels. It will work for such cases as long as required_outer is
* empty (otherwise get_baserel_parampathinfo does the wrong thing), which
* fortunately is the expected case for now.
*/
if (!bms_is_empty(required_outer) && !IS_SIMPLE_REL(rel))
elog(ERROR, "parameterized foreign joins are not supported yet");
pathnode->path.pathtype = T_ForeignScan;
pathnode->path.parent = rel;
pathnode->path.pathtarget = target ? target : rel->reltarget;

9
src/backend/optimizer/util/relnode.c
View File

@ -1247,6 +1247,9 @@ get_baserel_parampathinfo(PlannerInfo *root, RelOptInfo *baserel,
double rows;
ListCell *lc;
/* If rel has LATERAL refs, every path for it should account for them */
Assert(bms_is_subset(baserel->lateral_relids, required_outer));
/* Unparameterized paths have no ParamPathInfo */
if (bms_is_empty(required_outer))
return NULL;
@ -1342,6 +1345,9 @@ get_joinrel_parampathinfo(PlannerInfo *root, RelOptInfo *joinrel,
double rows;
ListCell *lc;
/* If rel has LATERAL refs, every path for it should account for them */
Assert(bms_is_subset(joinrel->lateral_relids, required_outer));
/* Unparameterized paths have no ParamPathInfo or extra join clauses */
if (bms_is_empty(required_outer))
return NULL;
@ -1533,6 +1539,9 @@ get_appendrel_parampathinfo(RelOptInfo *appendrel, Relids required_outer)
{
ParamPathInfo *ppi;
/* If rel has LATERAL refs, every path for it should account for them */
Assert(bms_is_subset(appendrel->lateral_relids, required_outer));
/* Unparameterized paths have no ParamPathInfo */
if (bms_is_empty(required_outer))
return NULL;