Disallow MERGE cleanly for foreign partitions

While directly targetting a foreign table with MERGE was already
expressly forbidden, we failed to catch the case of a partitioned table
that has a foreign table as a partition; and the result if you try is an
incomprehensible error.  Fix that by adding a specific check.

Backpatch to 15.

Reported-by: Tatsuhiro Nakamori <bt22nakamorit@oss.nttdata.com>
Discussion: https://postgr.es/m/bt22nakamorit@oss.nttdata.com

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 9746998751aa8a320cd8f4ac59110ecc606a21c5..b3c8ce01313d17cdae89c8837a757f99b4b89acd 100644 (file)
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -8284,6 +8284,11 @@ select tableoid::regclass, * FROM remp2;
 (3 rows)
 
 delete from itrtest;
+-- MERGE ought to fail cleanly
+merge into itrtest using (select 1, 'foo') as source on (true)
+  when matched then do nothing;
+ERROR:  cannot execute MERGE on relation "remp1"
+DETAIL:  This operation is not supported for foreign tables.
 create unique index loct1_idx on loct1 (a);
 -- DO NOTHING without an inference specification is supported
 insert into itrtest values (1, 'foo') on conflict do nothing returning *;

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 1962051e541128851bcf6e9e0078cbb91559ffa6..b0dbb41fb55370c6a6f10a94b002d36db184f8bb 100644 (file)
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -2207,6 +2207,10 @@ select tableoid::regclass, * FROM remp2;
 
 delete from itrtest;
 
+-- MERGE ought to fail cleanly
+merge into itrtest using (select 1, 'foo') as source on (true)
+  when matched then do nothing;
+
 create unique index loct1_idx on loct1 (a);
 
 -- DO NOTHING without an inference specification is supported

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index ab4d8e201df1653bd336ac675dc7fd1a44be6f49..ac86ce90033bcf677cd1b40dc02d8b0e00e6b5cd 100644 (file)
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -7078,12 +7078,32 @@ make_modifytable(PlannerInfo *root, Plan *subplan,
            RelOptInfo *resultRel = root->simple_rel_array[rti];
 
            fdwroutine = resultRel->fdwroutine;
+
+           /*
+            * MERGE is not currently supported for foreign tables and we
+            * already checked when the table mentioned in the query is
+            * foreign; but we can still get here if a partitioned table has a
+            * foreign table as partition.  Disallow that now, to avoid an
+            * uglier error message later.
+            */
+           if (operation == CMD_MERGE && fdwroutine != NULL)
+           {
+               RangeTblEntry *rte = root->simple_rte_array[rti];
+
+               ereport(ERROR,
+                       errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                       errmsg("cannot execute MERGE on relation \"%s\"",
+                              get_rel_name(rte->relid)),
+                       errdetail_relkind_not_supported(rte->relkind));
+           }
+
        }
        else
        {
            RangeTblEntry *rte = planner_rt_fetch(rti, root);
 
            Assert(rte->rtekind == RTE_RELATION);
+           Assert(operation != CMD_MERGE);
            if (rte->relkind == RELKIND_FOREIGN_TABLE)
                fdwroutine = GetFdwRoutineByRelId(rte->relid);
            else