Use the regular main processing loop also in walsenders.

The regular backend's main loop handles signal handling and error recovery
better than the current WAL sender command loop does. For example, if the
client hangs and a SIGTERM is received before starting streaming, the
walsender will now terminate immediately, rather than hang until the
connection times out.

src/backend/replication/basebackup.c

@@ -22,6 +22,7 @@
 #include "lib/stringinfo.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
+#include "miscadmin.h"
 #include "nodes/pg_list.h"
 #include "replication/basebackup.h"
 #include "replication/walsender.h"
@@ -30,7 +31,6 @@
 #include "storage/ipc.h"
 #include "utils/builtins.h"
 #include "utils/elog.h"
-#include "utils/memutils.h"
 #include "utils/ps_status.h"
 
 typedef struct
@@ -370,19 +370,10 @@ void
 SendBaseBackup(BaseBackupCmd *cmd)
 {
 	DIR		   *dir;
-	MemoryContext backup_context;
-	MemoryContext old_context;
 	basebackup_options opt;
 
 	parse_basebackup_options(cmd->options, &opt);
 
-	backup_context = AllocSetContextCreate(CurrentMemoryContext,
-										   "Streaming base backup context",
-										   ALLOCSET_DEFAULT_MINSIZE,
-										   ALLOCSET_DEFAULT_INITSIZE,
-										   ALLOCSET_DEFAULT_MAXSIZE);
-	old_context = MemoryContextSwitchTo(backup_context);
-
 	WalSndSetState(WALSNDSTATE_BACKUP);
 
 	if (update_process_title)
@@ -403,9 +394,6 @@ SendBaseBackup(BaseBackupCmd *cmd)
 	perform_base_backup(&opt, dir);
 
 	FreeDir(dir);
-
-	MemoryContextSwitchTo(old_context);
-	MemoryContextDelete(backup_context);
 }
 
 static void
@@ -606,7 +594,7 @@ sendDir(char *path, int basepathlen, bool sizeonly)
 		 * error in that case. The error handler further up will call
 		 * do_pg_abort_backup() for us.
 		 */
-		if (walsender_shutdown_requested || walsender_ready_to_stop)
+		if (ProcDiePending || walsender_ready_to_stop)
 			ereport(ERROR,
 				(errmsg("shutdown requested, aborting active base backup")));
 

src/backend/tcop/postgres.c

@@ -192,6 +192,7 @@ static int	InteractiveBackend(StringInfo inBuf);
 static int	interactive_getc(void);
 static int	SocketBackend(StringInfo inBuf);
 static int	ReadCommand(StringInfo inBuf);
+static void forbidden_in_wal_sender(char firstchar);
 static List *pg_rewrite_query(Query *query);
 static bool check_log_statement(List *stmt_list);
 static int	errdetail_execute(List *raw_parsetree_list);
@@ -3720,12 +3721,9 @@ PostgresMain(int argc, char *argv[], const char *username)
 	if (IsUnderPostmaster && Log_disconnections)
 		on_proc_exit(log_disconnections, 0);
 
-	/* If this is a WAL sender process, we're done with initialization. */
+	/* Perform initialization specific to a WAL sender process. */
 	if (am_walsender)
-	{
-		WalSenderMain();		/* does not return */
-		abort();
-	}
+		InitWalSender();
 
 	/*
 	 * process any libraries that should be preloaded at backend start (this
@@ -3835,6 +3833,9 @@ PostgresMain(int argc, char *argv[], const char *username)
 		 */
 		AbortCurrentTransaction();
 
+		if (am_walsender)
+			WalSndErrorCleanup();
+
 		/*
 		 * Now return to normal top-level context and clear ErrorContext for
 		 * next time.
@@ -3969,7 +3970,10 @@ PostgresMain(int argc, char *argv[], const char *username)
 					query_string = pq_getmsgstring(&input_message);
 					pq_getmsgend(&input_message);
 
-					exec_simple_query(query_string);
+					if (am_walsender)
+						exec_replication_command(query_string);
+					else
+						exec_simple_query(query_string);
 
 					send_ready_for_query = true;
 				}
@@ -3982,6 +3986,8 @@ PostgresMain(int argc, char *argv[], const char *username)
 					int			numParams;
 					Oid		   *paramTypes = NULL;
 
+					forbidden_in_wal_sender(firstchar);
+
 					/* Set statement_timestamp() */
 					SetCurrentStatementStartTimestamp();
 
@@ -4004,6 +4010,8 @@ PostgresMain(int argc, char *argv[], const char *username)
 				break;
 
 			case 'B':			/* bind */
+				forbidden_in_wal_sender(firstchar);
+
 				/* Set statement_timestamp() */
 				SetCurrentStatementStartTimestamp();
 
@@ -4019,6 +4027,8 @@ PostgresMain(int argc, char *argv[], const char *username)
 					const char *portal_name;
 					int			max_rows;
 
+					forbidden_in_wal_sender(firstchar);
+
 					/* Set statement_timestamp() */
 					SetCurrentStatementStartTimestamp();
 
@@ -4031,6 +4041,8 @@ PostgresMain(int argc, char *argv[], const char *username)
 				break;
 
 			case 'F':			/* fastpath function call */
+				forbidden_in_wal_sender(firstchar);
+
 				/* Set statement_timestamp() */
 				SetCurrentStatementStartTimestamp();
 
@@ -4078,6 +4090,8 @@ PostgresMain(int argc, char *argv[], const char *username)
 					int			close_type;
 					const char *close_target;
 
+					forbidden_in_wal_sender(firstchar);
+
 					close_type = pq_getmsgbyte(&input_message);
 					close_target = pq_getmsgstring(&input_message);
 					pq_getmsgend(&input_message);
@@ -4120,6 +4134,8 @@ PostgresMain(int argc, char *argv[], const char *username)
 					int			describe_type;
 					const char *describe_target;
 
+					forbidden_in_wal_sender(firstchar);
+
 					/* Set statement_timestamp() (needed for xact) */
 					SetCurrentStatementStartTimestamp();
 
@@ -4201,6 +4217,29 @@ PostgresMain(int argc, char *argv[], const char *username)
 	}							/* end of input-reading loop */
 }
 
+/*
+ * Throw an error if we're a WAL sender process.
+ *
+ * This is used to forbid anything else than simple query protocol messages
+ * in a WAL sender process.  'firstchar' specifies what kind of a forbidden
+ * message was received, and is used to construct the error message.
+ */
+static void
+forbidden_in_wal_sender(char firstchar)
+{
+	if (am_walsender)
+	{
+		if (firstchar == 'F')
+			ereport(ERROR,
+					(errcode(ERRCODE_PROTOCOL_VIOLATION),
+					 errmsg("fastpath function calls not supported in a replication connection")));
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_PROTOCOL_VIOLATION),
+					 errmsg("extended query protocol not supported in a replication connection")));
+	}
+}
+
 
 /*
  * Obtain platform stack depth limit (in bytes)

src/include/replication/walsender.h

@@ -19,7 +19,6 @@
 /* global state */
 extern bool am_walsender;
 extern bool am_cascading_walsender;
-extern volatile sig_atomic_t walsender_shutdown_requested;
 extern volatile sig_atomic_t walsender_ready_to_stop;
 extern bool wake_wal_senders;
 
@@ -27,7 +26,9 @@ extern bool wake_wal_senders;
 extern int	max_wal_senders;
 extern int	replication_timeout;
 
-extern void WalSenderMain(void) __attribute__((noreturn));
+extern void InitWalSender(void);
+extern void exec_replication_command(const char *query_string);
+extern void WalSndErrorCleanup(void);
 extern void WalSndSignals(void);
 extern Size WalSndShmemSize(void);
 extern void WalSndShmemInit(void);