Avoid invalidating all foreign-join cached plans when user mappings change.

We must not push down a foreign join when the foreign tables involved
should be accessed under different user mappings.  Previously we tried
to enforce that rule literally during planning, but that meant that the
resulting plans were dependent on the current contents of the
pg_user_mapping catalog, and we had to blow away all cached plans
containing any remote join when anything at all changed in pg_user_mapping.
This could have been improved somewhat, but the fact that a syscache inval
callback has very limited info about what changed made it hard to do better
within that design.  Instead, let's change the planner to not consider user
mappings per se, but to allow a foreign join if both RTEs have the same
checkAsUser value.  If they do, then they necessarily will use the same
user mapping at runtime, and we don't need to know specifically which one
that is.  Post-plan-time changes in pg_user_mapping no longer require any
plan invalidation.

This rule does give up some optimization ability, to wit where two foreign
table references come from views with different owners or one's from a view
and one's directly in the query, but nonetheless the same user mapping
would have applied.  We'll sacrifice the first case, but to not regress
more than we have to in the second case, allow a foreign join involving
both zero and nonzero checkAsUser values if the nonzero one is the same as
the prevailing effective userID.  In that case, mark the plan as only
runnable by that userID.

The plancache code already had a notion of plans being userID-specific,
in order to support RLS.  It was a little confused though, in particular
lacking clarity of thought as to whether it was the rewritten query or just
the finished plan that's dependent on the userID.  Rearrange that code so
that it's clearer what depends on which, and so that the same logic applies
to both RLS-injected role dependency and foreign-join-injected role
dependency.

Note that this patch doesn't remove the other issue mentioned in the
original complaint, which is that while we'll reliably stop using a foreign
join if it's disallowed in a new context, we might fail to start using a
foreign join if it's now allowed, but we previously created a generic
cached plan that didn't use one.  It was agreed that the chance of winning
that way was not high enough to justify the much larger number of plan
invalidations that would have to occur if we tried to cause it to happen.

In passing, clean up randomly-varying spelling of EXPLAIN commands in
postgres_fdw.sql, and fix a COSTS ON example that had been allowed to
leak into the committed tests.

This reverts most of commits fbe5a3fb and 5d4171d1, which were the
previous attempt at ensuring we wouldn't push down foreign joins that
span permissions contexts.

Etsuro Fujita and Tom Lane

Discussion: <d49c1e5b-f059-20f4-c132-e9752ee0113e@lab.ntt.co.jp>

contrib/postgres_fdw/postgres_fdw.c

@@ -67,8 +67,6 @@ enum FdwScanPrivateIndex
 	FdwScanPrivateRetrievedAttrs,
 	/* Integer representing the desired fetch_size */
 	FdwScanPrivateFetchSize,
-	/* Oid of user mapping to be used while connecting to the foreign server */
-	FdwScanPrivateUserMappingOid,
 
 	/*
 	 * String describing join i.e. names of relations being joined and types
@@ -1226,11 +1224,10 @@ postgresGetForeignPlan(PlannerInfo *root,
 	 * Build the fdw_private list that will be available to the executor.
 	 * Items in the list must match order in enum FdwScanPrivateIndex.
 	 */
-	fdw_private = list_make5(makeString(sql.data),
+	fdw_private = list_make4(makeString(sql.data),
 							 remote_conds,
 							 retrieved_attrs,
-							 makeInteger(fpinfo->fetch_size),
-							 makeInteger(foreignrel->umid));
+							 makeInteger(fpinfo->fetch_size));
 	if (foreignrel->reloptkind == RELOPT_JOINREL)
 		fdw_private = lappend(fdw_private,
 							  makeString(fpinfo->relation_name->data));
@@ -1262,7 +1259,11 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
 	ForeignScan *fsplan = (ForeignScan *) node->ss.ps.plan;
 	EState	   *estate = node->ss.ps.state;
 	PgFdwScanState *fsstate;
+	RangeTblEntry *rte;
+	Oid			userid;
+	ForeignTable *table;
 	UserMapping *user;
+	int			rtindex;
 	int			numParams;
 
 	/*
@@ -1278,36 +1279,20 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
 	node->fdw_state = (void *) fsstate;
 
 	/*
-	 * Obtain the foreign server where to connect and user mapping to use for
-	 * connection. For base relations we obtain this information from
-	 * catalogs. For join relations, this information is frozen at the time of
-	 * planning to ensure that the join is safe to pushdown. In case the
-	 * information goes stale between planning and execution, plan will be
-	 * invalidated and replanned.
+	 * Identify which user to do the remote access as.  This should match what
+	 * ExecCheckRTEPerms() does.  In case of a join, use the lowest-numbered
+	 * member RTE as a representative; we would get the same result from any.
 	 */
 	if (fsplan->scan.scanrelid > 0)
-	{
-		ForeignTable *table;
-
-		/*
-		 * Identify which user to do the remote access as.  This should match
-		 * what ExecCheckRTEPerms() does.
-		 */
-		RangeTblEntry *rte = rt_fetch(fsplan->scan.scanrelid, estate->es_range_table);
-		Oid			userid = rte->checkAsUser ? rte->checkAsUser : GetUserId();
-
-		fsstate->rel = node->ss.ss_currentRelation;
-		table = GetForeignTable(RelationGetRelid(fsstate->rel));
-
-		user = GetUserMapping(userid, table->serverid);
-	}
+		rtindex = fsplan->scan.scanrelid;
 	else
-	{
-		Oid			umid = intVal(list_nth(fsplan->fdw_private, FdwScanPrivateUserMappingOid));
+		rtindex = bms_next_member(fsplan->fs_relids, -1);
+	rte = rt_fetch(rtindex, estate->es_range_table);
+	userid = rte->checkAsUser ? rte->checkAsUser : GetUserId();
 
-		user = GetUserMappingById(umid);
-		Assert(fsplan->fs_server == user->serverid);
-	}
+	/* Get info about foreign table. */
+	table = GetForeignTable(rte->relid);
+	user = GetUserMapping(userid, table->serverid);
 
 	/*
 	 * Get connection to the foreign server.  Connection manager will
@@ -1344,9 +1329,15 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
 	 * into local representation and error reporting during that process.
 	 */
 	if (fsplan->scan.scanrelid > 0)
+	{
+		fsstate->rel = node->ss.ss_currentRelation;
 		fsstate->tupdesc = RelationGetDescr(fsstate->rel);
+	}
 	else
+	{
+		fsstate->rel = NULL;
 		fsstate->tupdesc = node->ss.ss_ScanTupleSlot->tts_tupleDescriptor;
+	}
 
 	fsstate->attinmeta = TupleDescGetAttInMetadata(fsstate->tupdesc);
 
@@ -3965,16 +3956,6 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	List	   *joinclauses;
 	List	   *otherclauses;
 
-	/*
-	 * Core code may call GetForeignJoinPaths hook even when the join relation
-	 * doesn't have a valid user mapping associated with it. See
-	 * build_join_rel() for details. We can't push down such join, since there
-	 * doesn't exist a user mapping which can be used to connect to the
-	 * foreign server.
-	 */
-	if (!OidIsValid(joinrel->umid))
-		return false;
-
 	/*
 	 * We support pushing down INNER, LEFT, RIGHT and FULL OUTER joins.
 	 * Constructing queries representing SEMI and ANTI joins is hard, hence
@@ -4151,6 +4132,20 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
 	fpinfo->use_remote_estimate = fpinfo_o->use_remote_estimate ||
 		fpinfo_i->use_remote_estimate;
 
+	/* Get user mapping */
+	if (fpinfo->use_remote_estimate)
+	{
+		if (fpinfo_o->use_remote_estimate)
+			fpinfo->user = fpinfo_o->user;
+		else
+			fpinfo->user = fpinfo_i->user;
+	}
+	else
+		fpinfo->user = NULL;
+
+	/* Get foreign server */
+	fpinfo->server = fpinfo_o->server;
+
 	/*
 	 * Since both the joining relations come from the same server, the server
 	 * level options should have same value for both the relations. Pick from
@@ -4312,26 +4307,14 @@ postgresGetForeignJoinPaths(PlannerInfo *root,
 	cost_qual_eval(&fpinfo->local_conds_cost, fpinfo->local_conds, root);
 
 	/*
-	 * If we are going to estimate the costs using EXPLAIN, we will need
-	 * connection information. Fill it here.
+	 * If we are going to estimate costs locally, estimate the join clause
+	 * selectivity here while we have special join info.
 	 */
-	if (fpinfo->use_remote_estimate)
-		fpinfo->user = GetUserMappingById(joinrel->umid);
-	else
-	{
-		fpinfo->user = NULL;
-
-		/*
-		 * If we are going to estimate costs locally, estimate the join clause
-		 * selectivity here while we have special join info.
-		 */
+	if (!fpinfo->use_remote_estimate)
 		fpinfo->joinclause_sel = clauselist_selectivity(root, fpinfo->joinclauses,
 														0, fpinfo->jointype,
 														extra->sjinfo);
 
-	}
-	fpinfo->server = GetForeignServer(joinrel->serverid);
-
 	/* Estimate costs for bare join relation */
 	estimate_path_cost_size(root, joinrel, NIL, NIL, &rows,
 							&width, &startup_cost, &total_cost);

src/backend/executor/execParallel.c

@@ -145,10 +145,12 @@ ExecSerializePlan(Plan *plan, EState *estate)
 	pstmt = makeNode(PlannedStmt);
 	pstmt->commandType = CMD_SELECT;
 	pstmt->queryId = 0;
-	pstmt->hasReturning = 0;
-	pstmt->hasModifyingCTE = 0;
-	pstmt->canSetTag = 1;
-	pstmt->transientPlan = 0;
+	pstmt->hasReturning = false;
+	pstmt->hasModifyingCTE = false;
+	pstmt->canSetTag = true;
+	pstmt->transientPlan = false;
+	pstmt->dependsOnRole = false;
+	pstmt->parallelModeNeeded = false;
 	pstmt->planTree = plan;
 	pstmt->rtable = estate->es_range_table;
 	pstmt->resultRelations = NIL;
@@ -156,11 +158,9 @@ ExecSerializePlan(Plan *plan, EState *estate)
 	pstmt->subplans = NIL;
 	pstmt->rewindPlanIDs = NULL;
 	pstmt->rowMarks = NIL;
-	pstmt->nParamExec = estate->es_plannedstmt->nParamExec;
 	pstmt->relationOids = NIL;
 	pstmt->invalItems = NIL;	/* workers can't replan anyway... */
-	pstmt->hasRowSecurity = false;
-	pstmt->hasForeignJoin = false;
+	pstmt->nParamExec = estate->es_plannedstmt->nParamExec;
 
 	/* Return serialized copy of our dummy PlannedStmt. */
 	return nodeToString(pstmt);

src/backend/foreign/foreign.c

@@ -31,7 +31,8 @@
 extern Datum pg_options_to_table(PG_FUNCTION_ARGS);
 extern Datum postgresql_fdw_validator(PG_FUNCTION_ARGS);
 
-static HeapTuple find_user_mapping(Oid userid, Oid serverid, bool missing_ok);
+static HeapTuple find_user_mapping(Oid userid, Oid serverid);
+
 
 /*
  * GetForeignDataWrapper -	look up the foreign-data wrapper by OID.
@@ -223,7 +224,7 @@ GetUserMapping(Oid userid, Oid serverid)
 	bool		isnull;
 	UserMapping *um;
 
-	tp = find_user_mapping(userid, serverid, false);
+	tp = find_user_mapping(userid, serverid);
 
 	um = (UserMapping *) palloc(sizeof(UserMapping));
 	um->umid = HeapTupleGetOid(tp);
@@ -250,23 +251,14 @@ GetUserMapping(Oid userid, Oid serverid)
  *
  * If no mapping is found for the supplied user, we also look for
  * PUBLIC mappings (userid == InvalidOid).
- *
- * If missing_ok is true, the function returns InvalidOid when it does not find
- * required user mapping. Otherwise, find_user_mapping() throws error if it
- * does not find required user mapping.
  */
 Oid
-GetUserMappingId(Oid userid, Oid serverid, bool missing_ok)
+GetUserMappingId(Oid userid, Oid serverid)
 {
 	HeapTuple	tp;
 	Oid			umid;
 
-	tp = find_user_mapping(userid, serverid, missing_ok);
-
-	Assert(missing_ok || tp);
-
-	if (!tp && missing_ok)
-		return InvalidOid;
+	tp = find_user_mapping(userid, serverid);
 
 	/* Extract the Oid */
 	umid = HeapTupleGetOid(tp);
@@ -276,19 +268,14 @@ GetUserMappingId(Oid userid, Oid serverid, bool missing_ok)
 	return umid;
 }
 
-
 /*
  * find_user_mapping - Guts of GetUserMapping family.
  *
  * If no mapping is found for the supplied user, we also look for
  * PUBLIC mappings (userid == InvalidOid).
- *
- * If missing_ok is true, the function returns NULL, if it does not find
- * the required user mapping. Otherwise, it throws error if it does not
- * find the required user mapping.
  */
 static HeapTuple
-find_user_mapping(Oid userid, Oid serverid, bool missing_ok)
+find_user_mapping(Oid userid, Oid serverid)
 {
 	HeapTuple	tp;
 
@@ -305,15 +292,10 @@ find_user_mapping(Oid userid, Oid serverid, bool missing_ok)
 						 ObjectIdGetDatum(serverid));
 
 	if (!HeapTupleIsValid(tp))
-	{
-		if (missing_ok)
-			return NULL;
-		else
-			ereport(ERROR,
-					(errcode(ERRCODE_UNDEFINED_OBJECT),
-					 errmsg("user mapping not found for \"%s\"",
-							MappingUserName(userid))));
-	}
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("user mapping not found for \"%s\"",
+						MappingUserName(userid))));
 
 	return tp;
 }

src/backend/nodes/copyfuncs.c

@@ -85,6 +85,8 @@ _copyPlannedStmt(const PlannedStmt *from)
 	COPY_SCALAR_FIELD(hasModifyingCTE);
 	COPY_SCALAR_FIELD(canSetTag);
 	COPY_SCALAR_FIELD(transientPlan);
+	COPY_SCALAR_FIELD(dependsOnRole);
+	COPY_SCALAR_FIELD(parallelModeNeeded);
 	COPY_NODE_FIELD(planTree);
 	COPY_NODE_FIELD(rtable);
 	COPY_NODE_FIELD(resultRelations);
@@ -95,9 +97,6 @@ _copyPlannedStmt(const PlannedStmt *from)
 	COPY_NODE_FIELD(relationOids);
 	COPY_NODE_FIELD(invalItems);
 	COPY_SCALAR_FIELD(nParamExec);
-	COPY_SCALAR_FIELD(hasRowSecurity);
-	COPY_SCALAR_FIELD(parallelModeNeeded);
-	COPY_SCALAR_FIELD(hasForeignJoin);
 
 	return newnode;
 }

src/backend/nodes/outfuncs.c

@@ -261,6 +261,8 @@ _outPlannedStmt(StringInfo str, const PlannedStmt *node)
 	WRITE_BOOL_FIELD(hasModifyingCTE);
 	WRITE_BOOL_FIELD(canSetTag);
 	WRITE_BOOL_FIELD(transientPlan);
+	WRITE_BOOL_FIELD(dependsOnRole);
+	WRITE_BOOL_FIELD(parallelModeNeeded);
 	WRITE_NODE_FIELD(planTree);
 	WRITE_NODE_FIELD(rtable);
 	WRITE_NODE_FIELD(resultRelations);
@@ -271,9 +273,6 @@ _outPlannedStmt(StringInfo str, const PlannedStmt *node)
 	WRITE_NODE_FIELD(relationOids);
 	WRITE_NODE_FIELD(invalItems);
 	WRITE_INT_FIELD(nParamExec);
-	WRITE_BOOL_FIELD(hasRowSecurity);
-	WRITE_BOOL_FIELD(parallelModeNeeded);
-	WRITE_BOOL_FIELD(hasForeignJoin);
 }
 
 /*
@@ -2014,11 +2013,11 @@ _outPlannerGlobal(StringInfo str, const PlannerGlobal *node)
 	WRITE_INT_FIELD(nParamExec);
 	WRITE_UINT_FIELD(lastPHId);
 	WRITE_UINT_FIELD(lastRowMarkId);
+	WRITE_INT_FIELD(lastPlanNodeId);
 	WRITE_BOOL_FIELD(transientPlan);
-	WRITE_BOOL_FIELD(hasRowSecurity);
+	WRITE_BOOL_FIELD(dependsOnRole);
 	WRITE_BOOL_FIELD(parallelModeOK);
 	WRITE_BOOL_FIELD(parallelModeNeeded);
-	WRITE_BOOL_FIELD(hasForeignJoin);
 }
 
 static void
@@ -2106,7 +2105,10 @@ _outRelOptInfo(StringInfo str, const RelOptInfo *node)
 	WRITE_FLOAT_FIELD(allvisfrac, "%.6f");
 	WRITE_NODE_FIELD(subroot);
 	WRITE_NODE_FIELD(subplan_params);
+	WRITE_INT_FIELD(rel_parallel_workers);
 	WRITE_OID_FIELD(serverid);
+	WRITE_OID_FIELD(userid);
+	WRITE_BOOL_FIELD(useridiscurrent);
 	/* we don't try to print fdwroutine or fdw_private */
 	WRITE_NODE_FIELD(baserestrictinfo);
 	WRITE_NODE_FIELD(joininfo);

src/backend/nodes/readfuncs.c

@@ -1390,6 +1390,8 @@ _readPlannedStmt(void)
 	READ_BOOL_FIELD(hasModifyingCTE);
 	READ_BOOL_FIELD(canSetTag);
 	READ_BOOL_FIELD(transientPlan);
+	READ_BOOL_FIELD(dependsOnRole);
+	READ_BOOL_FIELD(parallelModeNeeded);
 	READ_NODE_FIELD(planTree);
 	READ_NODE_FIELD(rtable);
 	READ_NODE_FIELD(resultRelations);
@@ -1400,9 +1402,6 @@ _readPlannedStmt(void)
 	READ_NODE_FIELD(relationOids);
 	READ_NODE_FIELD(invalItems);
 	READ_INT_FIELD(nParamExec);
-	READ_BOOL_FIELD(hasRowSecurity);
-	READ_BOOL_FIELD(parallelModeNeeded);
-	READ_BOOL_FIELD(hasForeignJoin);
 
 	READ_DONE();
 }

src/backend/optimizer/path/joinpath.c

@@ -213,8 +213,8 @@ add_paths_to_joinrel(PlannerInfo *root,
 
 	/*
 	 * 5. If inner and outer relations are foreign tables (or joins) belonging
-	 * to the same server and using the same user mapping, give the FDW a
-	 * chance to push down joins.
+	 * to the same server and assigned to the same user to check access
+	 * permissions as, give the FDW a chance to push down joins.
 	 */
 	if (joinrel->fdwroutine &&
 		joinrel->fdwroutine->GetForeignJoinPaths)

src/backend/optimizer/plan/createplan.c

@@ -3247,13 +3247,12 @@ create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
 	scan_plan->fs_relids = best_path->path.parent->relids;
 
 	/*
-	 * If a join between foreign relations was pushed down, remember it. The
-	 * push-down safety of the join depends upon the server and user mapping
-	 * being same. That can change between planning and execution time, in
-	 * which case the plan should be invalidated.
+	 * If this is a foreign join, and to make it valid to push down we had to
+	 * assume that the current user is the same as some user explicitly named
+	 * in the query, mark the finished plan as depending on the current user.
 	 */
-	if (scan_relid == 0)
-		root->glob->hasForeignJoin = true;
+	if (rel->useridiscurrent)
+		root->glob->dependsOnRole = true;
 
 	/*
 	 * Replace any outer-relation variables with nestloop params in the qual,

src/backend/optimizer/plan/planner.c

@@ -219,8 +219,7 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	glob->lastRowMarkId = 0;
 	glob->lastPlanNodeId = 0;
 	glob->transientPlan = false;
-	glob->hasRowSecurity = false;
-	glob->hasForeignJoin = false;
+	glob->dependsOnRole = false;
 
 	/*
 	 * Assess whether it's feasible to use parallel mode for this query. We
@@ -405,6 +404,8 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	result->hasModifyingCTE = parse->hasModifyingCTE;
 	result->canSetTag = parse->canSetTag;
 	result->transientPlan = glob->transientPlan;
+	result->dependsOnRole = glob->dependsOnRole;
+	result->parallelModeNeeded = glob->parallelModeNeeded;
 	result->planTree = top_plan;
 	result->rtable = glob->finalrtable;
 	result->resultRelations = glob->resultRelations;
@@ -415,9 +416,6 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	result->relationOids = glob->relationOids;
 	result->invalItems = glob->invalItems;
 	result->nParamExec = glob->nParamExec;
-	result->hasRowSecurity = glob->hasRowSecurity;
-	result->parallelModeNeeded = glob->parallelModeNeeded;
-	result->hasForeignJoin = glob->hasForeignJoin;
 
 	return result;
 }
@@ -1628,8 +1626,6 @@ grouping_planner(PlannerInfo *root, bool inheritance_update,
 		 * This may add new security barrier subquery RTEs to the rangetable.
 		 */
 		expand_security_quals(root, tlist);
-		if (parse->hasRowSecurity)
-			root->glob->hasRowSecurity = true;
 
 		/*
 		 * We are now done hacking up the query's targetlist.  Most of the
@@ -1960,7 +1956,8 @@ grouping_planner(PlannerInfo *root, bool inheritance_update,
 	 * If the current_rel belongs to a single FDW, so does the final_rel.
 	 */
 	final_rel->serverid = current_rel->serverid;
-	final_rel->umid = current_rel->umid;
+	final_rel->userid = current_rel->userid;
+	final_rel->useridiscurrent = current_rel->useridiscurrent;
 	final_rel->fdwroutine = current_rel->fdwroutine;
 
 	/*
@@ -3337,7 +3334,8 @@ create_grouping_paths(PlannerInfo *root,
 	 * If the input rel belongs to a single FDW, so does the grouped rel.
 	 */
 	grouped_rel->serverid = input_rel->serverid;
-	grouped_rel->umid = input_rel->umid;
+	grouped_rel->userid = input_rel->userid;
+	grouped_rel->useridiscurrent = input_rel->useridiscurrent;
 	grouped_rel->fdwroutine = input_rel->fdwroutine;
 
 	/*
@@ -3891,7 +3889,8 @@ create_window_paths(PlannerInfo *root,
 	 * If the input rel belongs to a single FDW, so does the window rel.
 	 */
 	window_rel->serverid = input_rel->serverid;
-	window_rel->umid = input_rel->umid;
+	window_rel->userid = input_rel->userid;
+	window_rel->useridiscurrent = input_rel->useridiscurrent;
 	window_rel->fdwroutine = input_rel->fdwroutine;
 
 	/*
@@ -4071,7 +4070,8 @@ create_distinct_paths(PlannerInfo *root,
 	 * If the input rel belongs to a single FDW, so does the distinct_rel.
 	 */
 	distinct_rel->serverid = input_rel->serverid;
-	distinct_rel->umid = input_rel->umid;
+	distinct_rel->userid = input_rel->userid;
+	distinct_rel->useridiscurrent = input_rel->useridiscurrent;
 	distinct_rel->fdwroutine = input_rel->fdwroutine;
 
 	/* Estimate number of distinct rows there will be */
@@ -4279,7 +4279,8 @@ create_ordered_paths(PlannerInfo *root,
 	 * If the input rel belongs to a single FDW, so does the ordered_rel.
 	 */
 	ordered_rel->serverid = input_rel->serverid;
-	ordered_rel->umid = input_rel->umid;
+	ordered_rel->userid = input_rel->userid;
+	ordered_rel->useridiscurrent = input_rel->useridiscurrent;
 	ordered_rel->fdwroutine = input_rel->fdwroutine;
 
 	foreach(lc, input_rel->pathlist)

src/backend/optimizer/plan/setrefs.c

@@ -2432,9 +2432,10 @@ record_plan_function_dependency(PlannerInfo *root, Oid funcid)
 
 /*
  * extract_query_dependencies
- *		Given a not-yet-planned query or queries (i.e. a Query node or list
- *		of Query nodes), extract dependencies just as set_plan_references
- *		would do.
+ *		Given a rewritten, but not yet planned, query or queries
+ *		(i.e. a Query node or list of Query nodes), extract dependencies
+ *		just as set_plan_references would do.  Also detect whether any
+ *		rewrite steps were affected by RLS.
  *
  * This is needed by plancache.c to handle invalidation of cached unplanned
  * queries.
@@ -2453,7 +2454,8 @@ extract_query_dependencies(Node *query,
 	glob.type = T_PlannerGlobal;
 	glob.relationOids = NIL;
 	glob.invalItems = NIL;
-	glob.hasRowSecurity = false;
+	/* Hack: we use glob.dependsOnRole to collect hasRowSecurity flags */
+	glob.dependsOnRole = false;
 
 	MemSet(&root, 0, sizeof(root));
 	root.type = T_PlannerInfo;
@@ -2463,7 +2465,7 @@ extract_query_dependencies(Node *query,
 
 	*relationOids = glob.relationOids;
 	*invalItems = glob.invalItems;
-	*hasRowSecurity = glob.hasRowSecurity;
+	*hasRowSecurity = glob.dependsOnRole;
 }
 
 static bool
@@ -2479,10 +2481,6 @@ extract_query_dependencies_walker(Node *node, PlannerInfo *context)
 		Query	   *query = (Query *) node;
 		ListCell   *lc;
 
-		/* Collect row security information */
-		if (query->hasRowSecurity)
-			context->glob->hasRowSecurity = true;
-
 		if (query->commandType == CMD_UTILITY)
 		{
 			/*
@@ -2494,6 +2492,10 @@ extract_query_dependencies_walker(Node *node, PlannerInfo *context)
 				return false;
 		}
 
+		/* Remember if any Query has RLS quals applied by rewriter */
+		if (query->hasRowSecurity)
+			context->glob->dependsOnRole = true;
+
 		/* Collect relation OIDs in this Query's rtable */
 		foreach(lc, query->rtable)
 		{

src/backend/optimizer/util/relnode.c

@@ -15,8 +15,6 @@
 #include "postgres.h"
 
 #include "miscadmin.h"
-#include "catalog/pg_class.h"
-#include "foreign/foreign.h"
 #include "optimizer/clauses.h"
 #include "optimizer/cost.h"
 #include "optimizer/pathnode.h"
@@ -107,7 +105,6 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->consider_startup = (root->tuple_fraction > 0);
 	rel->consider_param_startup = false;		/* might get changed later */
 	rel->consider_parallel = false;		/* might get changed later */
-	rel->rel_parallel_workers = -1;		/* set up in GetRelationInfo */
 	rel->reltarget = create_empty_pathtarget();
 	rel->pathlist = NIL;
 	rel->ppilist = NIL;
@@ -129,8 +126,10 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 	rel->allvisfrac = 0;
 	rel->subroot = NULL;
 	rel->subplan_params = NIL;
+	rel->rel_parallel_workers = -1;		/* set up in GetRelationInfo */
 	rel->serverid = InvalidOid;
-	rel->umid = InvalidOid;
+	rel->userid = rte->checkAsUser;
+	rel->useridiscurrent = false;
 	rel->fdwroutine = NULL;
 	rel->fdw_private = NULL;
 	rel->baserestrictinfo = NIL;
@@ -170,30 +169,6 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 			break;
 	}
 
-	/* For foreign tables get the user mapping */
-	if (rte->relkind == RELKIND_FOREIGN_TABLE)
-	{
-		/*
-		 * This should match what ExecCheckRTEPerms() does.
-		 *
-		 * Note that if the plan ends up depending on the user OID in any way
-		 * - e.g. if it depends on the computed user mapping OID - we must
-		 * ensure that it gets invalidated in the case of a user OID change.
-		 * See RevalidateCachedQuery and more generally the hasForeignJoin
-		 * flags in PlannerGlobal and PlannedStmt.
-		 *
-		 * It's possible, and not necessarily an error, for rel->umid to be
-		 * InvalidOid even though rel->serverid is set.  That just means there
-		 * is a server with no user mapping.
-		 */
-		Oid			userid;
-
-		userid = OidIsValid(rte->checkAsUser) ? rte->checkAsUser : GetUserId();
-		rel->umid = GetUserMappingId(userid, rel->serverid, true);
-	}
-	else
-		rel->umid = InvalidOid;
-
 	/* Save the finished struct in the query's simple_rel_array */
 	root->simple_rel_array[relid] = rel;
 
@@ -423,8 +398,10 @@ build_join_rel(PlannerInfo *root,
 	joinrel->allvisfrac = 0;
 	joinrel->subroot = NULL;
 	joinrel->subplan_params = NIL;
+	joinrel->rel_parallel_workers = -1;
 	joinrel->serverid = InvalidOid;
-	joinrel->umid = InvalidOid;
+	joinrel->userid = InvalidOid;
+	joinrel->useridiscurrent = false;
 	joinrel->fdwroutine = NULL;
 	joinrel->fdw_private = NULL;
 	joinrel->baserestrictinfo = NIL;
@@ -435,24 +412,43 @@ build_join_rel(PlannerInfo *root,
 
 	/*
 	 * Set up foreign-join fields if outer and inner relation are foreign
-	 * tables (or joins) belonging to the same server and using the same user
-	 * mapping.
-	 *
-	 * Otherwise those fields are left invalid, so FDW API will not be called
-	 * for the join relation.
+	 * tables (or joins) belonging to the same server and assigned to the same
+	 * user to check access permissions as.  In addition to an exact match of
+	 * userid, we allow the case where one side has zero userid (implying
+	 * current user) and the other side has explicit userid that happens to
+	 * equal the current user; but in that case, pushdown of the join is only
+	 * valid for the current user.  The useridiscurrent field records whether
+	 * we had to make such an assumption for this join or any sub-join.
 	 *
-	 * For FDWs like file_fdw, which ignore user mapping, the user mapping id
-	 * associated with the joining relation may be invalid. A valid serverid
-	 * distinguishes between a pushed down join with no user mapping and a
-	 * join which can not be pushed down because of user mapping mismatch.
+	 * Otherwise these fields are left invalid, so GetForeignJoinPaths will
+	 * not be called for the join relation.
 	 */
 	if (OidIsValid(outer_rel->serverid) &&
-		inner_rel->serverid == outer_rel->serverid &&
-		inner_rel->umid == outer_rel->umid)
+		inner_rel->serverid == outer_rel->serverid)
 	{
-		joinrel->serverid = outer_rel->serverid;
-		joinrel->umid = outer_rel->umid;
-		joinrel->fdwroutine = outer_rel->fdwroutine;
+		if (inner_rel->userid == outer_rel->userid)
+		{
+			joinrel->serverid = outer_rel->serverid;
+			joinrel->userid = outer_rel->userid;
+			joinrel->useridiscurrent = outer_rel->useridiscurrent || inner_rel->useridiscurrent;
+			joinrel->fdwroutine = outer_rel->fdwroutine;
+		}
+		else if (!OidIsValid(inner_rel->userid) &&
+				 outer_rel->userid == GetUserId())
+		{
+			joinrel->serverid = outer_rel->serverid;
+			joinrel->userid = outer_rel->userid;
+			joinrel->useridiscurrent = true;
+			joinrel->fdwroutine = outer_rel->fdwroutine;
+		}
+		else if (!OidIsValid(outer_rel->userid) &&
+				 inner_rel->userid == GetUserId())
+		{
+			joinrel->serverid = outer_rel->serverid;
+			joinrel->userid = inner_rel->userid;
+			joinrel->useridiscurrent = true;
+			joinrel->fdwroutine = outer_rel->fdwroutine;
+		}
 	}
 
 	/*

src/include/foreign/foreign.h

@@ -72,7 +72,7 @@ typedef struct ForeignTable
 extern ForeignServer *GetForeignServer(Oid serverid);
 extern ForeignServer *GetForeignServerByName(const char *name, bool missing_ok);
 extern UserMapping *GetUserMapping(Oid userid, Oid serverid);
-extern Oid	GetUserMappingId(Oid userid, Oid serverid, bool missing_ok);
+extern Oid	GetUserMappingId(Oid userid, Oid serverid);
 extern UserMapping *GetUserMappingById(Oid umid);
 extern ForeignDataWrapper *GetForeignDataWrapper(Oid fdwid);
 extern ForeignDataWrapper *GetForeignDataWrapperByName(const char *name,

src/include/nodes/parsenodes.h

@@ -121,7 +121,7 @@ typedef struct Query
 	bool		hasRecursive;	/* WITH RECURSIVE was specified */
 	bool		hasModifyingCTE;	/* has INSERT/UPDATE/DELETE in WITH */
 	bool		hasForUpdate;	/* FOR [KEY] UPDATE/SHARE was specified */
-	bool		hasRowSecurity; /* row security applied? */
+	bool		hasRowSecurity; /* rewriter has applied some RLS policy */
 
 	List	   *cteList;		/* WITH list (of CommonTableExpr's) */
 
@@ -2823,7 +2823,7 @@ typedef enum VacuumOption
 	VACOPT_FULL = 1 << 4,		/* FULL (non-concurrent) vacuum */
 	VACOPT_NOWAIT = 1 << 5,		/* don't wait to get lock (autovacuum only) */
 	VACOPT_SKIPTOAST = 1 << 6,	/* don't process the TOAST table, if any */
-	VACOPT_DISABLE_PAGE_SKIPPING = 1 << 7	/* don't skip any pages */
+	VACOPT_DISABLE_PAGE_SKIPPING = 1 << 7		/* don't skip any pages */
 } VacuumOption;
 
 typedef struct VacuumStmt

src/include/nodes/plannodes.h

@@ -49,6 +49,10 @@ typedef struct PlannedStmt
 
 	bool		transientPlan;	/* redo plan when TransactionXmin changes? */
 
+	bool		dependsOnRole;	/* is plan specific to current role? */
+
+	bool		parallelModeNeeded;		/* parallel mode required to execute? */
+
 	struct Plan *planTree;		/* tree of Plan nodes */
 
 	List	   *rtable;			/* list of RangeTblEntry nodes */
@@ -69,11 +73,6 @@ typedef struct PlannedStmt
 	List	   *invalItems;		/* other dependencies, as PlanInvalItems */
 
 	int			nParamExec;		/* number of PARAM_EXEC Params used */
-
-	bool		hasRowSecurity; /* row security applied? */
-
-	bool		parallelModeNeeded;		/* parallel mode required to execute? */
-	bool		hasForeignJoin; /* Plan has a pushed down foreign join */
 } PlannedStmt;
 
 /* macro for fetching the Plan associated with a SubPlan node */

src/include/nodes/relation.h

@@ -121,13 +121,11 @@ typedef struct PlannerGlobal
 
 	bool		transientPlan;	/* redo plan when TransactionXmin changes? */
 
-	bool		hasRowSecurity; /* row security applied? */
+	bool		dependsOnRole;	/* is plan specific to current role? */
 
 	bool		parallelModeOK; /* parallel mode potentially OK? */
 
 	bool		parallelModeNeeded;		/* parallel mode actually required? */
-
-	bool		hasForeignJoin; /* does have a pushed down foreign join */
 } PlannerGlobal;
 
 /* macro for fetching the Plan associated with a SubPlan node */
@@ -426,11 +424,12 @@ typedef struct PlannerInfo
  *		in just as for a baserel, except we don't bother with lateral_vars.
  *
  * If the relation is either a foreign table or a join of foreign tables that
- * all belong to the same foreign server and use the same user mapping, these
- * fields will be set:
+ * all belong to the same foreign server and are assigned to the same user to
+ * check access permissions as (cf checkAsUser), these fields will be set:
  *
  *		serverid - OID of foreign server, if foreign table (else InvalidOid)
- *		umid - OID of user mapping, if foreign table (else InvalidOid)
+ *		userid - OID of user to check access as (InvalidOid means current user)
+ *		useridiscurrent - we've assumed that userid equals current user
  *		fdwroutine - function hooks for FDW, if foreign table (else NULL)
  *		fdw_private - private state for FDW, if foreign table (else NULL)
  *
@@ -528,8 +527,8 @@ typedef struct RelOptInfo
 
 	/* Information about foreign tables and foreign joins */
 	Oid			serverid;		/* identifies server for the table or join */
-	Oid			umid;			/* identifies user mapping for the table or
-								 * join */
+	Oid			userid;			/* identifies user to check access as */
+	bool		useridiscurrent;	/* join is only valid for current user */
 	/* use "struct FdwRoutine" to avoid including fdwapi.h here */
 	struct FdwRoutine *fdwroutine;
 	void	   *fdw_private;
@@ -653,7 +652,7 @@ typedef struct ForeignKeyOptInfo
 	struct EquivalenceClass *eclass[INDEX_MAX_KEYS];
 	/* List of non-EC RestrictInfos matching each column's condition */
 	List	   *rinfos[INDEX_MAX_KEYS];
-}	ForeignKeyOptInfo;
+} ForeignKeyOptInfo;
 
 
 /*

src/include/utils/plancache.h

@@ -93,8 +93,10 @@ typedef struct CachedPlanSource
 	List	   *invalItems;		/* other dependencies, as PlanInvalItems */
 	struct OverrideSearchPath *search_path;		/* search_path used for
 												 * parsing and planning */
-	Oid			planUserId;		/* User-id that the plan depends on */
 	MemoryContext query_context;	/* context holding the above, or NULL */
+	Oid			rewriteRoleId;	/* Role ID we did rewriting for */
+	bool		rewriteRowSecurity;		/* row_security used during rewrite */
+	bool		dependsOnRLS;	/* is rewritten query specific to the above? */
 	/* If we have a generic plan, this is a reference-counted link to it: */
 	struct CachedPlan *gplan;	/* generic plan, or NULL if not valid */
 	/* Some state flags: */
@@ -109,8 +111,6 @@ typedef struct CachedPlanSource
 	double		generic_cost;	/* cost of generic plan, or -1 if not known */
 	double		total_custom_cost;		/* total cost of custom plans so far */
 	int			num_custom_plans;		/* number of plans included in total */
-	bool		hasRowSecurity; /* planned with row security? */
-	bool		row_security_env;		/* row security setting when planned */
 } CachedPlanSource;
 
 /*
@@ -131,11 +131,12 @@ typedef struct CachedPlan
 	bool		is_oneshot;		/* is it a "oneshot" plan? */
 	bool		is_saved;		/* is CachedPlan in a long-lived context? */
 	bool		is_valid;		/* is the stmt_list currently valid? */
+	Oid			planRoleId;		/* Role ID the plan was created for */
+	bool		dependsOnRole;	/* is plan specific to that role? */
 	TransactionId saved_xmin;	/* if valid, replan when TransactionXmin
 								 * changes from this value */
 	int			generation;		/* parent's generation number for this plan */
 	int			refcount;		/* count of live references to this struct */
-	bool		has_foreign_join;		/* plan has pushed down a foreign join */
 	MemoryContext context;		/* context containing this CachedPlan */
 } CachedPlan;