Rework read-only mode: use Postgres native DefaultXactReadOnly

include/spock_readonly.h

@@ -11,7 +11,7 @@
 typedef enum SpockReadonlyMode
 {
 	READONLY_OFF,
-	READONLY_USER,
+	READONLY_LOCAL,
 	READONLY_ALL
 } SpockReadonlyMode;
 

src/spock.c

@@ -115,7 +115,8 @@ static const struct config_enum_entry exception_logging_options[] = {
 
 static const struct config_enum_entry readonly_options[] = {
 	{"off", READONLY_OFF, false},
-	{"user", READONLY_USER, false},
+	{"local", READONLY_LOCAL, false},
+	{"user", READONLY_LOCAL, true},	/* backward-compatible alias */
 	{"all", READONLY_ALL, false},
 	{NULL, 0, false}
 };

src/spock_apply.c

@@ -2412,7 +2412,7 @@ replication_handler(StringInfo s)
 	char		action = pq_getmsgbyte(s);
 
 	if (spock_readonly == READONLY_ALL)
-		elog(ERROR, "SPOCK %s: cluster is in read-only mode, not performing replication",
+		elog(PANIC, "SPOCK %s: cluster is in read-only mode, not performing replication",
 			 MySubscription->name);
 
 	memset(&errcallback_arg, 0, sizeof(struct ActionErrCallbackArg));
@@ -2869,9 +2869,48 @@ apply_work(PGconn *streamConn)
 				StringInfo	msg;
 				int			c;
 
+				CHECK_FOR_INTERRUPTS();
+
 				if (got_SIGTERM)
 					break;
 
+				if (ConfigReloadPending)
+				{
+					ConfigReloadPending = false;
+					ProcessConfigFile(PGC_SIGHUP);
+				}
+
+				/*
+				 * Do not apply new transactions if cluster is switched to
+				 * the readonly mode.
+				 */
+				if (spock_readonly == READONLY_ALL)
+				{
+					/*
+					 * Send feedback to keep walsender alive - we may avoid it
+					 * with introduction of TCP keepalive approach.
+					 */
+					maybe_send_feedback(applyconn, last_received,
+										&last_receive_timestamp);
+
+					/*
+					 * In case of an exception we can't break out of the loop
+					 * because exception processing code may also modify the
+					 * database. Wait briefly and continue to the next iteration.
+					 */
+					if (xact_had_exception)
+					{
+						rc = WaitLatchOrSocket(&MyProc->procLatch,
+								   WL_SOCKET_READABLE | WL_LATCH_SET |
+								   WL_TIMEOUT | WL_POSTMASTER_DEATH,
+								   fd, 1000L);
+
+						ResetLatch(&MyProc->procLatch);
+						continue;
+					}
+					break;
+				}
+
 				if (apply_replay_next == NULL)
 				{
 					char	   *buf;
@@ -2927,12 +2966,6 @@ apply_work(PGconn *streamConn)
 					queue_append = false;
 				}
 
-				if (ConfigReloadPending)
-				{
-					ConfigReloadPending = false;
-					ProcessConfigFile(PGC_SIGHUP);
-				}
-
 				/* Handle the message received or replayed */
 				msg = &entry->copydata;
 				msg->cursor = 0;
@@ -3050,8 +3083,6 @@ apply_work(PGconn *streamConn)
 
 				/* We must not have fallen out of MessageContext by accident */
 				Assert(CurrentMemoryContext == MessageContext);
-
-				CHECK_FOR_INTERRUPTS();
 			}
 
 			if (xact_had_exception)

src/spock_readonly.c

@@ -2,9 +2,12 @@
  * spock_readonly.c
  *    Spock readonly related functions
  *
- * Spock readonly functions allow setting the entire cluster to read-only mode,
- * preventing INSERT, UPDATE, DELETE, and DDL operations. This file is part of
- * pgEdge, Inc. open source project, licensed under the PostgreSQL license.
+ * Spock readonly functions allow setting the database to read-only mode,
+ * preventing INSERT, UPDATE, DELETE, and DDL operations.
+ * In the 'ALL' mode it prevents the database from being modified by spock
+ * apply workers as well.
+ * This code employs the transaction_read_only GUC to disable attempts
+ * to execute DML or DDL commands.
  *
  * This file is part of pgEdge, Inc. open source project, licensed under
  * the PostgreSQL license. For license terms, see the LICENSE file.
@@ -62,56 +65,53 @@ spockro_terminate_active_transactions(PG_FUNCTION_ARGS)
 void
 spock_ropost_parse_analyze(ParseState *pstate, Query *query, JumbleState *jstate)
 {
-	bool		command_is_ro = false;
+	/*
+	 * If spock.readonly is set, enforce Postgres core restriction for the
+	 * following query. We actively employ the fact that the core uses the
+	 * XactReadOnly value directly, not through the GetConfigOption function.
+	 * Also, we use this fact here to identify if XactReadOnly has been changed
+	 * by Spock or by external tools.
+	 */
+	if (spock_readonly >= READONLY_LOCAL && !superuser())
+		XactReadOnly = true;
+	else if (XactReadOnly)
+	{
+		const char *value =
+						GetConfigOption("transaction_read_only", false, false);
 
-	switch (query->commandType)
+		if (strcmp(value, "off") == 0)
+			/* Spock imposed read-only. Restore the original state. */
+			XactReadOnly = false;
+	}
+	else
 	{
-		case CMD_SELECT:
-			command_is_ro = true;
-			break;
-		case CMD_UTILITY:
-			switch (nodeTag(query->utilityStmt))
-			{
-				case T_AlterSystemStmt:
-				case T_DeallocateStmt:
-				case T_ExecuteStmt:
-				case T_ExplainStmt:
-				case T_PrepareStmt:
-				case T_TransactionStmt:
-				case T_VariableSetStmt:
-				case T_VariableShowStmt:
-					command_is_ro = true;
-					break;
-				default:
-					command_is_ro = false;
-					break;
-			}
-			break;
-		default:
-			command_is_ro = false;
-			break;
+		/* XactReadOnly is already false, nothing to restore. */
 	}
-	if (spock_readonly >= READONLY_USER && !command_is_ro)
-		ereport(ERROR, (errmsg("spock: invalid statement for a read-only cluster")));
 }
 
 void
 spock_roExecutorStart(QueryDesc *queryDesc, int eflags)
 {
-	bool		command_is_ro = false;
+	/*
+	 * Let's do the same job as at parse analysis hook.
+	 *
+	 * In some cases parse analysis and planning may be skipped on repeated
+	 * execution (remember SPI plan for example). So, additional control makes
+	 * sense here.
+	 */
+	if (spock_readonly >= READONLY_LOCAL && !superuser())
+		XactReadOnly = true;
+	else if (XactReadOnly)
+	{
+		const char *value =
+						GetConfigOption("transaction_read_only", false, false);
 
-	switch (queryDesc->operation)
+		if (strcmp(value, "off") == 0)
+			/* Spock imposed read-only. Restore the original state. */
+			XactReadOnly = false;
+	}
+	else
 	{
-		case CMD_SELECT:
-			command_is_ro = true;
-			break;
-		case CMD_INSERT:
-		case CMD_UPDATE:
-		case CMD_DELETE:
-		default:
-			command_is_ro = false;
-			break;
+		/* XactReadOnly is already false, nothing to restore. */
 	}
-	if (spock_readonly >= READONLY_USER && !command_is_ro)
-		ereport(ERROR, (errmsg("spock: invalid statement for a read-only cluster")));
 }