Rewrite btree vacuuming to fold the former bulkdelete and cleanup operations

into a single mostly-physical-order scan of the index.  This requires some
ticklish interlocking considerations, but should create no material
performance impact on normal index operations (at least given the
already-committed changes to make scans work a page at a time).  VACUUM
itself should get significantly faster in any index that's degenerated to a
very nonlinear page order.  Also, we save one pass over the index entirely,
except in the case where there were no deletions to do and so only one pass
happened anyway.

Original patch by Heikki Linnakangas, rework by Tom Lane.

src/backend/storage/ipc/ipci.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/ipc/ipci.c,v 1.82 2006/03/05 15:58:37 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/ipc/ipci.c,v 1.83 2006/05/08 00:00:10 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -16,6 +16,7 @@
 
 #include "access/clog.h"
 #include "access/multixact.h"
+#include "access/nbtree.h"
 #include "access/subtrans.h"
 #include "access/twophase.h"
 #include "access/xlog.h"
@@ -88,6 +89,7 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
 		size = add_size(size, SInvalShmemSize());
 		size = add_size(size, FreeSpaceShmemSize());
 		size = add_size(size, BgWriterShmemSize());
+		size = add_size(size, BTreeShmemSize());
 #ifdef EXEC_BACKEND
 		size = add_size(size, ShmemBackendArraySize());
 #endif
@@ -182,6 +184,11 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
 	PMSignalInit();
 	BgWriterShmemInit();
 
+	/*
+	 * Set up other modules that need some shared memory space
+	 */
+	BTreeShmemInit();
+
 #ifdef EXEC_BACKEND
 
 	/*