Prohibit combining publications with different column lists.

Currently, we simply combine the column lists when publishing tables on
multiple publications and that can sometimes lead to unexpected behavior.
Say, if a column is published in any row-filtered publication, then the
values for that column are sent to the subscriber even for rows that don't
match the row filter, as long as the row matches the row filter for any
other publication, even if that other publication doesn't include the
column.

The main purpose of introducing a column list is to have statically
different shapes on publisher and subscriber or hide sensitive column
data. In both cases, it doesn't seem to make sense to combine column
lists.

So, we disallow the cases where the column list is different for the same
table when combining publications. It can be later extended to combine the
column lists for selective cases where required.

Reported-by: Alvaro Herrera
Author: Hou Zhijie
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/202204251548.mudq7jbqnh7r@alvherre.pgsql

1 files changed, 38 insertions, 34 deletions

diff --git a/src/backend/replication/logical/tablesync.c b/src/backend/replication/logical/tablesync.c
index 994c7a09d92..670c6fcada5 100644
--- a/src/backend/replication/logical/tablesync.c
+++ b/src/backend/replication/logical/tablesync.c
@@ -753,17 +753,6 @@ fetch_remote_table_info(char *nspname, char *relname,
 	/*
 	 * Get column lists for each relation.
 	 *
-	 * For initial synchronization, column lists can be ignored in following
-	 * cases:
-	 *
-	 * 1) one of the subscribed publications for the table hasn't specified
-	 * any column list
-	 *
-	 * 2) one of the subscribed publications has puballtables set to true
-	 *
-	 * 3) one of the subscribed publications is declared as ALL TABLES IN
-	 * SCHEMA that includes this relation
-	 *
 	 * We need to do this before fetching info about column names and types,
 	 * so that we can skip columns that should not be replicated.
 	 */
@@ -771,7 +760,7 @@ fetch_remote_table_info(char *nspname, char *relname,
 	{
 		WalRcvExecResult *pubres;
 		TupleTableSlot *slot;
-		Oid			attrsRow[] = {INT2OID};
+		Oid			attrsRow[] = {INT2VECTOROID};
 		StringInfoData pub_names;
 		bool		first = true;
 
@@ -786,19 +775,17 @@ fetch_remote_table_info(char *nspname, char *relname,
 
 		/*
 		 * Fetch info about column lists for the relation (from all the
-		 * publications). We unnest the int2vector values, because that makes
-		 * it easier to combine lists by simply adding the attnums to a new
-		 * bitmap (without having to parse the int2vector data). This
-		 * preserves NULL values, so that if one of the publications has no
-		 * column list, we'll know that.
+		 * publications).
 		 */
 		resetStringInfo(&cmd);
 		appendStringInfo(&cmd,
-						 "SELECT DISTINCT unnest"
+						 "SELECT DISTINCT"
+						 "  (CASE WHEN (array_length(gpt.attrs, 1) = c.relnatts)"
+						 "   THEN NULL ELSE gpt.attrs END)"
 						 "  FROM pg_publication p,"
-						 "  LATERAL pg_get_publication_tables(p.pubname) gpt"
-						 "  LEFT OUTER JOIN unnest(gpt.attrs) ON TRUE"
-						 " WHERE gpt.relid = %u"
+						 "  LATERAL pg_get_publication_tables(p.pubname) gpt,"
+						 "  pg_class c"
+						 " WHERE gpt.relid = %u AND c.oid = gpt.relid"
 						 "   AND p.pubname IN ( %s )",
 						 lrel->remoteid,
 						 pub_names.data);
@@ -813,26 +800,43 @@ fetch_remote_table_info(char *nspname, char *relname,
 							nspname, relname, pubres->err)));
 
 		/*
-		 * Merge the column lists (from different publications) by creating a
-		 * single bitmap with all the attnums. If we find a NULL value, that
-		 * means one of the publications has no column list for the table
-		 * we're syncing.
+		 * We don't support the case where the column list is different for
+		 * the same table when combining publications. See comments atop
+		 * fetch_table_list. So there should be only one row returned.
+		 * Although we already checked this when creating the subscription, we
+		 * still need to check here in case the column list was changed after
+		 * creating the subscription and before the sync worker is started.
+		 */
+		if (tuplestore_tuple_count(pubres->tuplestore) > 1)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("cannot use different column lists for table \"%s.%s\" in different publications",
+						   nspname, relname));
+
+		/*
+		 * Get the column list and build a single bitmap with the attnums.
+		 *
+		 * If we find a NULL value, it means all the columns should be
+		 * replicated.
 		 */
 		slot = MakeSingleTupleTableSlot(pubres->tupledesc, &TTSOpsMinimalTuple);
-		while (tuplestore_gettupleslot(pubres->tuplestore, true, false, slot))
+		if (tuplestore_gettupleslot(pubres->tuplestore, true, false, slot))
 		{
 			Datum		cfval = slot_getattr(slot, 1, &isnull);
 
-			/* NULL means empty column list, so we're done. */
-			if (isnull)
+			if (!isnull)
 			{
-				bms_free(included_cols);
-				included_cols = NULL;
-				break;
-			}
+				ArrayType  *arr;
+				int			nelems;
+				int16	   *elems;
 
-			included_cols = bms_add_member(included_cols,
-										   DatumGetInt16(cfval));
+				arr = DatumGetArrayTypeP(cfval);
+				nelems = ARR_DIMS(arr)[0];
+				elems = (int16 *) ARR_DATA_PTR(arr);
+
+				for (natt = 0; natt < nelems; natt++)
+					included_cols = bms_add_member(included_cols, elems[natt]);
+			}
 
 			ExecClearTuple(slot);
 		}