Rethink the way walreceiver is linked into the backend. Instead than shoving

walreceiver as whole into a dynamically loaded module, split the
libpq-specific parts of it into dynamically loaded module and keep the rest
in the main backend binary.

Although Tom fixed the Windows compilation problems with the old walreceiver
module already, this is a cleaner division of labour and makes the code
more readable. There's also the prospect of adding new transport methods
as pluggable modules in the future, which this patch makes easier, though for
now the API between libpqwalreceiver and walreceiver process should be
considered private.

The libpq-specific module is now in src/backend/replication/libpqwalreceiver,
and the part linked with postgres binary is in
src/backend/replication/walreceiver.c.

Author: hlinnaka

src/Makefile

@@ -4,7 +4,7 @@
 #
 # Copyright (c) 1994, Regents of the University of California
 #
-# $PostgreSQL: pgsql/src/Makefile,v 1.49 2010/01/15 17:01:06 heikki Exp $
+# $PostgreSQL: pgsql/src/Makefile,v 1.50 2010/01/20 09:16:23 heikki Exp $
 #
 #-------------------------------------------------------------------------
 
@@ -21,7 +21,7 @@ all install installdirs uninstall distprep:
 	$(MAKE) -C backend/snowball $@
 	$(MAKE) -C include $@
 	$(MAKE) -C interfaces $@
-	$(MAKE) -C backend/replication/walreceiver $@
+	$(MAKE) -C backend/replication/libpqwalreceiver $@
 	$(MAKE) -C bin $@
 	$(MAKE) -C pl $@
 	$(MAKE) -C makefiles $@
@@ -52,7 +52,7 @@ clean:
 	$(MAKE) -C backend/snowball $@
 	$(MAKE) -C include $@
 	$(MAKE) -C interfaces $@
-	$(MAKE) -C backend/replication/walreceiver $@
+	$(MAKE) -C backend/replication/libpqwalreceiver $@
 	$(MAKE) -C bin $@
 	$(MAKE) -C pl $@
 	$(MAKE) -C makefiles $@
@@ -67,7 +67,7 @@ distclean maintainer-clean:
 	$(MAKE) -C backend/snowball $@
 	$(MAKE) -C include $@
 	$(MAKE) -C interfaces $@
-	$(MAKE) -C backend/replication/walreceiver $@
+	$(MAKE) -C backend/replication/libpqwalreceiver $@
 	$(MAKE) -C bin $@
 	$(MAKE) -C pl $@
 	$(MAKE) -C makefiles $@
@@ -82,7 +82,7 @@ coverage:
 	$(MAKE) -C backend/utils/mb/conversion_procs $@
 	$(MAKE) -C backend/snowball $@
 	$(MAKE) -C interfaces $@
-	$(MAKE) -C backend/replication/walreceiver $@
+	$(MAKE) -C backend/replication/libpqwalreceiver $@
 	$(MAKE) -C bin $@
 	$(MAKE) -C pl $@
 

src/backend/bootstrap/bootstrap.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/bootstrap/bootstrap.c,v 1.256 2010/01/15 09:19:00 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/bootstrap/bootstrap.c,v 1.257 2010/01/20 09:16:23 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -425,20 +425,7 @@ AuxiliaryProcessMain(int argc, char *argv[])
 
 		case WalReceiverProcess:
 			/* don't set signals, walreceiver has its own agenda */
-			{
-				PGFunction WalReceiverMain;
-
-				/*
-				 * Walreceiver is not linked directly into the server
-				 * binary because we would then need to link the server
-				 * with libpq. It's compiled as a dynamically loaded module
-				 * to avoid that.
-				 */
-				WalReceiverMain = load_external_function("walreceiver",
-														 "WalReceiverMain",
-														 true, NULL);
-				WalReceiverMain(NULL);
-			}
+			WalReceiverMain();
 			proc_exit(1);		/* should never return */
 
 		default:

src/backend/replication/Makefile

@@ -4,14 +4,14 @@
 #    Makefile for src/backend/replication
 #
 # IDENTIFICATION
-#    $PostgreSQL: pgsql/src/backend/replication/Makefile,v 1.1 2010/01/15 09:19:03 heikki Exp $
+#    $PostgreSQL: pgsql/src/backend/replication/Makefile,v 1.2 2010/01/20 09:16:24 heikki Exp $
 #
 #-------------------------------------------------------------------------
 
 subdir = src/backend/replication
 top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
-OBJS = walsender.o walreceiverfuncs.o
+OBJS = walsender.o walreceiverfuncs.o walreceiver.o
 
 include $(top_srcdir)/src/backend/common.mk

src/backend/replication/README

@@ -1,4 +1,36 @@
-$PostgreSQL: pgsql/src/backend/replication/README,v 1.1 2010/01/15 09:19:03 heikki Exp $
+$PostgreSQL: pgsql/src/backend/replication/README,v 1.2 2010/01/20 09:16:24 heikki Exp $
+
+Walreceiver - libpqwalreceiver API
+----------------------------------
+
+The transport-specific part of walreceiver, responsible for connecting to
+the primary server and receiving WAL files, is loaded dynamically to avoid
+having to link the main server binary with libpq. The dynamically loaded
+module is in libpqwalreceiver subdirectory.
+
+The dynamically loaded module implements three functions:
+
+
+bool walrcv_connect(char *conninfo, XLogRecPtr startpoint)
+
+Establish connection to the primary, and starts streaming from 'startpoint'.
+Returns true on success.
+
+
+bool walrcv_receive(int timeout, XLogRecPtr *recptr, char **buffer, int *len)
+
+Retrieve any WAL record available through the connection, blocking for
+maximum of 'timeout' ms.
+
+
+void walrcv_disconnect(void);
+
+Disconnect.
+
+
+This API should be considered internal at the moment, but we could open it
+up for 3rd party replacements of libpqwalreceiver in the future, allowing
+pluggable methods for receiveing WAL.
 
 Walreceiver IPC
 ---------------

src/backend/replication/walreceiver/Makefile renamed to src/backend/replication/libpqwalreceiver/Makefile

@@ -1,24 +1,22 @@
 #-------------------------------------------------------------------------
 #
 # Makefile--
-#    Makefile for src/backend/replication/walreceiver
+#    Makefile for src/backend/replication/libpqwalreceiver
 #
 # IDENTIFICATION
-#    $PostgreSQL: pgsql/src/backend/replication/walreceiver/Makefile,v 1.4 2010/01/15 21:06:26 tgl Exp $
+#    $PostgreSQL: pgsql/src/backend/replication/libpqwalreceiver/Makefile,v 1.1 2010/01/20 09:16:24 heikki Exp $
 #
 #-------------------------------------------------------------------------
 
-subdir = src/backend/replication/walreceiver
+subdir = src/backend/postmaster/libpqwalreceiver
 top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
-override CPPFLAGS := -I$(libpq_srcdir) $(CPPFLAGS)
-
-OBJS = walreceiver.o
+override CPPFLAGS := -I$(srcdir) -I$(libpq_srcdir) $(CPPFLAGS)
 
+OBJS = libpqwalreceiver.o
 SHLIB_LINK = $(libpq)
-
-NAME := walreceiver
+NAME = libpqwalreceiver
 
 all: submake-libpq all-shared-lib