Separate snapshot management code from tuple visibility code, create a

snapmgmt.c file for the former.  The header files have also been reorganized
in three parts: the most basic snapshot definitions are now in a new file
snapshot.h, and the also new snapmgmt.h keeps the definitions for snapmgmt.c.
tqual.h has been reduced to the bare minimum.

This patch is just a first step towards managing live snapshots within a
transaction; there is no functionality change.

Per my proposal to pgsql-patches on 20080318191940.GB27458@alvh.no-ip.org and
subsequent discussion.

src/backend/access/heap/heapam.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.251 2008/03/08 21:57:59 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.252 2008/03/26 16:20:46 alvherre Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -56,6 +56,7 @@
 #include "utils/inval.h"
 #include "utils/lsyscache.h"
 #include "utils/relcache.h"
+#include "utils/snapmgmt.h"
 #include "utils/syscache.h"
 
 

src/backend/access/index/indexam.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/index/indexam.c,v 1.101 2008/01/01 19:45:46 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/index/indexam.c,v 1.102 2008/03/26 16:20:46 alvherre Exp $
  *
  * INTERFACE ROUTINES
  *		index_open		- open an index relation by relation OID
@@ -67,6 +67,7 @@
 #include "access/transam.h"
 #include "pgstat.h"
 #include "utils/relcache.h"
+#include "utils/snapmgmt.h"
 
 
 /* ----------------------------------------------------------------

src/backend/access/nbtree/nbtpage.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtpage.c,v 1.106 2008/01/01 19:45:46 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtpage.c,v 1.107 2008/03/26 16:20:46 alvherre Exp $
  *
  *	NOTES
  *	   Postgres btree pages look like ordinary relation pages.	The opaque
@@ -28,6 +28,7 @@
 #include "storage/freespace.h"
 #include "storage/lmgr.h"
 #include "utils/inval.h"
+#include "utils/snapmgmt.h"
 
 
 /*

src/backend/access/transam/subtrans.c

@@ -22,7 +22,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/subtrans.c,v 1.20 2008/01/01 19:45:48 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/subtrans.c,v 1.21 2008/03/26 16:20:46 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -31,7 +31,7 @@
 #include "access/slru.h"
 #include "access/subtrans.h"
 #include "access/transam.h"
-#include "utils/tqual.h"
+#include "utils/snapmgmt.h"
 
 
 /*

src/backend/access/transam/transam.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.74 2008/03/11 20:20:35 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.75 2008/03/26 16:20:46 alvherre Exp $
  *
  * NOTES
  *	  This file contains the high level access-method interface to the
@@ -22,7 +22,7 @@
 #include "access/clog.h"
 #include "access/subtrans.h"
 #include "access/transam.h"
-#include "utils/tqual.h"
+#include "utils/snapmgmt.h"
 
 
 /*

src/backend/access/transam/xact.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.260 2008/03/17 19:44:41 petere Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.261 2008/03/26 16:20:46 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -45,6 +45,7 @@
 #include "utils/inval.h"
 #include "utils/memutils.h"
 #include "utils/relcache.h"
+#include "utils/snapmgmt.h"
 #include "utils/xml.h"
 #include "pg_trace.h"