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/commands/cluster.c

@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/cluster.c,v 1.169 2008/01/30 19:46:48 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/cluster.c,v 1.170 2008/03/26 16:20:46 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -41,6 +41,7 @@
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/relcache.h"
+#include "utils/snapmgmt.h"
 #include "utils/syscache.h"
 
 

src/backend/commands/copy.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/copy.c,v 1.296 2008/03/08 01:16:26 adunstan Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/copy.c,v 1.297 2008/03/26 16:20:46 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -40,6 +40,7 @@
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
+#include "utils/snapmgmt.h"
 
 
 #define ISOCTAL(c) (((c) >= '0') && ((c) <= '7'))

src/backend/commands/explain.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994-5, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.169 2008/01/01 19:45:49 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.170 2008/03/26 16:20:46 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -31,6 +31,7 @@
 #include "utils/guc.h"
 #include "utils/lsyscache.h"
 #include "utils/tuplesort.h"
+#include "utils/snapmgmt.h"
 
 
 /* Hook for plugins to get control in ExplainOneQuery() */

src/backend/commands/indexcmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/indexcmds.c,v 1.171 2008/02/07 17:09:51 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/indexcmds.c,v 1.172 2008/03/26 16:20:46 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -47,6 +47,7 @@
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/relcache.h"
+#include "utils/snapmgmt.h"
 #include "utils/syscache.h"
 
 

src/backend/commands/portalcmds.c

@@ -14,7 +14,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/portalcmds.c,v 1.70 2008/03/20 20:05:56 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/portalcmds.c,v 1.71 2008/03/26 16:20:46 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -28,6 +28,7 @@
 #include "executor/executor.h"
 #include "tcop/pquery.h"
 #include "utils/memutils.h"
+#include "utils/snapmgmt.h"
 
 
 /*

src/backend/commands/prepare.c

@@ -10,7 +10,7 @@
  * Copyright (c) 2002-2008, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.82 2008/03/25 22:42:42 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.83 2008/03/26 16:20:46 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -32,6 +32,7 @@
 #include "tcop/utility.h"
 #include "utils/builtins.h"
 #include "utils/memutils.h"
+#include "utils/snapmgmt.h"
 
 
 /*

src/backend/commands/tablecmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.244 2008/03/25 22:42:42 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.245 2008/03/26 16:20:47 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -65,6 +65,7 @@
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/relcache.h"
+#include "utils/snapmgmt.h"
 #include "utils/syscache.h"
 
 

src/backend/commands/trigger.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.227 2008/01/02 23:34:42 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.228 2008/03/26 16:20:47 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -38,6 +38,7 @@
 #include "utils/inval.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
+#include "utils/snapmgmt.h"
 #include "utils/syscache.h"
 
 

src/backend/commands/vacuum.c

@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.368 2008/03/19 14:18:21 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.369 2008/03/26 16:20:47 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -48,6 +48,7 @@
 #include "utils/memutils.h"
 #include "utils/pg_rusage.h"
 #include "utils/relcache.h"
+#include "utils/snapmgmt.h"
 #include "utils/syscache.h"
 #include "pgstat.h"
 

src/backend/commands/variable.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/variable.c,v 1.125 2008/01/03 21:23:15 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/variable.c,v 1.126 2008/03/26 16:20:47 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -25,7 +25,7 @@
 #include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/syscache.h"
-#include "utils/tqual.h"
+#include "utils/snapmgmt.h"
 #include "mb/pg_wchar.h"
 
 /*