Better error message for unsupported replication cases - Mailing list pgsql-hackers

In [1] there's a complaint that if you try to logically replicate
a partitioned table from v13-or-later to v12-or-earlier, you get
"table XXX not found on publisher", which is pretty confusing
because the publisher certainly does have such a table.  That
happens because fetch_remote_table_info is too aggressive about
filtering by relkind and doesn't see the relation at all.
c314c147c improved that, but it wasn't back-patched.  I propose
putting the attached into v10-v12.  Maybe the error message
could be bikeshedded ... is "non-table relation" terminology
that we use in user-facing messages?

            regards, tom lane

[1] https://www.postgresql.org/message-id/CANhtRiamAgYt1A-Nh4%3DmU3E1UhG9XPgB%2BX6mW1DWqa93vUXW9A%40mail.gmail.com

diff --git a/src/backend/replication/logical/tablesync.c b/src/backend/replication/logical/tablesync.c
index 2db88dc41a..61244e08fa 100644
--- a/src/backend/replication/logical/tablesync.c
+++ b/src/backend/replication/logical/tablesync.c
@@ -646,9 +646,10 @@ fetch_remote_table_info(char *nspname, char *relname,
     WalRcvExecResult *res;
     StringInfoData cmd;
     TupleTableSlot *slot;
-    Oid            tableRow[2] = {OIDOID, CHAROID};
+    Oid            tableRow[3] = {OIDOID, CHAROID, CHAROID};
     Oid            attrRow[4] = {TEXTOID, OIDOID, INT4OID, BOOLOID};
     bool        isnull;
+    char        relkind;
     int            natt;

     lrel->nspname = nspname;
@@ -656,13 +657,12 @@ fetch_remote_table_info(char *nspname, char *relname,

     /* First fetch Oid and replica identity. */
     initStringInfo(&cmd);
-    appendStringInfo(&cmd, "SELECT c.oid, c.relreplident"
+    appendStringInfo(&cmd, "SELECT c.oid, c.relreplident, c.relkind"
                      "  FROM pg_catalog.pg_class c"
                      "  INNER JOIN pg_catalog.pg_namespace n"
                      "        ON (c.relnamespace = n.oid)"
                      " WHERE n.nspname = %s"
-                     "   AND c.relname = %s"
-                     "   AND c.relkind = 'r'",
+                     "   AND c.relname = %s",
                      quote_literal_cstr(nspname),
                      quote_literal_cstr(relname));
     res = walrcv_exec(LogRepWorkerWalRcvConn, cmd.data,
@@ -683,6 +683,19 @@ fetch_remote_table_info(char *nspname, char *relname,
     Assert(!isnull);
     lrel->replident = DatumGetChar(slot_getattr(slot, 2, &isnull));
     Assert(!isnull);
+    relkind = DatumGetChar(slot_getattr(slot, 3, &isnull));
+    Assert(!isnull);
+
+    /*
+     * Newer PG versions allow things that aren't plain tables to appear in
+     * publications.  We don't handle that in this version, but try to provide
+     * a useful error message.
+     */
+    if (relkind != RELKIND_RELATION)
+        ereport(ERROR,
+                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                 errmsg("cannot sync from non-table relation \"%s.%s\"",
+                        nspname, relname)));

     ExecDropSingleTupleTableSlot(slot);
     walrcv_clear_result(res);