Introduce wal_level GUC to explicitly control if information needed for

archival or hot standby should be WAL-logged, instead of deducing that from
other options like archive_mode. This replaces recovery_connections GUC in
the primary, where it now has no effect, but it's still used in the standby
to enable/disable hot standby.

Remove the WAL-logging of "unlogged operations", like creating an index
without WAL-logging and fsyncing it at the end. Instead, we keep a copy of
the wal_mode setting and the settings that affect how much shared memory a
hot standby server needs to track master transactions (max_connections,
max_prepared_xacts, max_locks_per_xact) in pg_control. Whenever the settings
change, at server restart, write a WAL record noting the new settings and
update pg_control. This allows us to notice the change in those settings in
the standby at the right moment, they used to be included in checkpoint
records, but that meant that a changed value was not reflected in the
standby until the first checkpoint after the change.

Bump PG_CONTROL_VERSION and XLOG_PAGE_MAGIC. Whack XLOG_PAGE_MAGIC back to
the sequence it used to follow, before hot standby and subsequent patches
changed it to 0x9003.

src/include/replication/walsender.h

@@ -5,7 +5,7 @@
  *
  * Portions Copyright (c) 2010-2010, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/include/replication/walsender.h,v 1.2 2010/02/26 02:01:27 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/replication/walsender.h,v 1.3 2010/04/28 16:10:43 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -39,6 +39,7 @@ extern bool am_walsender;
 
 /* user-settable parameters */
 extern int	WalSndDelay;
+extern int	max_wal_senders;
 
 extern int	WalSenderMain(void);
 extern void WalSndSignals(void);