Clean GUC placeholders with reserved prefix.

Extensions can reserve prefixes for their configuration parameters
while loading. Then all parameter placeholders with reserved prefixes
are removed from GUC list. Multimaster GUC list should also be cleaned.

Author: Andrei Kruchinin

expected/regression_ee.diff

@@ -1755,64 +1755,6 @@ diff ../../../src/test/regress/expected/subscription.out ../tmp_check/regress_ou
 
  ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
  DROP SUBSCRIPTION regress_testsub;
-diff ../../../src/test/regress/expected/guc.out ../tmp_check/regress_outdir/results/guc.out
---- ../../../src/test/regress/expected/guc.out	CENSORED
-+++ ../tmp_check/regress_outdir/results/guc.out	CENSORED
-@@ -563,13 +563,14 @@
- -- Test DISCARD TEMP
- --
- CREATE TEMP TABLE reset_test ( data text ) ON COMMIT DELETE ROWS;
-+ERROR:  unrecognized configuration parameter "plpgsql.extra_foo_warnings"
- SELECT relname FROM pg_class WHERE relname = 'reset_test';
--  relname   
--------------
-- reset_test
--(1 row)
-+ relname 
-+---------
-+(0 rows)
- 
- DISCARD TEMP;
-+ERROR:  unrecognized configuration parameter "plpgsql.extra_foo_warnings"
- SELECT relname FROM pg_class WHERE relname = 'reset_test';
-  relname 
- ---------
-@@ -584,8 +585,11 @@
- LISTEN foo_event;
- SET vacuum_cost_delay = 13;
- CREATE TEMP TABLE tmp_foo (data text) ON COMMIT DELETE ROWS;
-+ERROR:  unrecognized configuration parameter "plpgsql.extra_foo_warnings"
- CREATE ROLE regress_guc_user;
-+ERROR:  unrecognized configuration parameter "plpgsql.extra_foo_warnings"
- SET SESSION AUTHORIZATION regress_guc_user;
-+ERROR:  role "regress_guc_user" does not exist
- -- look changes
- SELECT pg_listening_channels();
-  pg_listening_channels 
-@@ -614,13 +618,12 @@
- SELECT relname from pg_class where relname = 'tmp_foo';
-  relname 
- ---------
-- tmp_foo
--(1 row)
-+(0 rows)
- 
- SELECT current_user = 'regress_guc_user';
-  ?column? 
- ----------
-- t
-+ f
- (1 row)
- 
- -- discard everything
-@@ -659,6 +662,7 @@
- (1 row)
- 
- DROP ROLE regress_guc_user;
-+ERROR:  role "regress_guc_user" does not exist
- --
- -- search_path should react to changes in pg_namespace
- --
 diff ../../../src/test/regress/expected/prepare.out ../tmp_check/regress_outdir/results/prepare.out
 --- ../../../src/test/regress/expected/prepare.out	CENSORED
 +++ ../tmp_check/regress_outdir/results/prepare.out	CENSORED

src/ddl.c

@@ -141,6 +141,7 @@ static void MtmProcessUtilitySender(PlannedStmt *pstmt,
 static void MtmGucUpdate(const char *key);
 static void MtmInitializeRemoteFunctionsMap(void);
 static char *MtmGucSerialize(void);
+static void MtmGucSync(const char *prefix);
 static void MtmMakeRelationLocal(Oid relid, bool locked);
 static List *AdjustCreateSequence(List *options);
 
@@ -638,6 +639,71 @@ MtmGucSerialize(void)
 	return serialized_gucs->data;
 }
 
+/*
+ * Any loaded extension can set ist own parameters
+ * replacing existing placeholders if needed
+ * and reserve its own parameter pefix.
+ * Then all remaining placeholders with this prefix are deleted.
+ * Multimaster guc list MtmGucEntry should be updated also.
+ * This version just removes parameters which:
+ * - have reserved prefixes,
+ * - are not in guc variables list now.
+ *
+ * XXX: Can module name be used as a reserved prefix?
+ *
+ * XXX: Is it better to store placeholder flag in MtmGucEntry?
+ *
+ */
+void
+MtmGucSync(const char *prefix)
+{
+	dlist_mutable_iter	iter;
+
+	if (!MtmGucHash)
+		MtmGucInit();
+
+	dlist_foreach_modify(iter, &MtmGucList)
+	{
+		MtmGucEntry *cur_entry = dlist_container(MtmGucEntry, list_node, iter.cur);
+		struct config_generic *gconf;
+		bool is_reserved_class = false;
+		const char *sep = strchr(cur_entry->key, GUC_QUALIFIER_SEPARATOR);
+		size_t classLen;
+		ListCell *lc;
+
+		if (sep == NULL)
+			/* leave if is not prefixed */
+			continue;
+
+		classLen = sep - cur_entry->key;
+		foreach(lc, reserved_class_prefix)
+		{
+			const char *rcprefix = lfirst(lc);
+
+			if (strlen(rcprefix) == classLen &&
+				strncmp(cur_entry->key, rcprefix, classLen) == 0)
+			{
+				elog(LOG, "----> MtmGucSerialize: invalid configuration parameter name \"%s\": "
+					"\"%s\" is a reserved prefix.",
+					cur_entry->key, rcprefix);
+				is_reserved_class = true;
+				break;
+			}
+		}
+
+		if (!is_reserved_class)
+			/* leave if prefix is not rerserved */
+			continue;
+
+		gconf = fing_guc_conf(cur_entry->key);
+		if (gconf)
+			/* leave if is in guc variable list */
+			continue;
+
+		dlist_delete(iter.cur);
+		hash_search(MtmGucHash, cur_entry->key, HASH_REMOVE, NULL);
+	}
+}
 
 
 /*****************************************************************************
@@ -1226,6 +1292,14 @@ MtmProcessUtilitySender(PlannedStmt *pstmt, const char *queryString, bool readOn
 		}
 	}
 
+	/* Catch GUC changes after LOAD */
+	if (nodeTag(parsetree) == T_LoadStmt)
+	{
+		LoadStmt *stmt = (LoadStmt *) parsetree;
+
+		MtmGucSync(stmt->filename);
+	}
+
 	if (executed)
 	{
 		MtmFinishDDLCommand();

src/multimaster.c

@@ -717,6 +717,8 @@ NULL);
 			NULL);
 	}
 
+	MarkGUCPrefixReserved("multimaster");
+
 	/*
 	 * Request additional shared resources.	 (These are no-ops if we're not in
 	 * the postmaster process.)	 We'll allocate or attach to the shared