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.

6 files changed, 106 insertions, 68 deletions

diff --git a/src/include/access/relscan.h b/src/include/access/relscan.h
index 62a0276fd0..eebcc86bb3 100644
--- a/src/include/access/relscan.h
+++ b/src/include/access/relscan.h
@@ -7,16 +7,17 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/relscan.h,v 1.60 2008/01/14 01:39:09 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/access/relscan.h,v 1.61 2008/03/26 16:20:48 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
 #ifndef RELSCAN_H
 #define RELSCAN_H
 
+#include "access/htup.h"
 #include "access/skey.h"
 #include "storage/bufpage.h"
-#include "utils/tqual.h"
+#include "utils/snapshot.h"
 
 
 typedef struct HeapScanDescData
diff --git a/src/include/storage/large_object.h b/src/include/storage/large_object.h
index 5d538e3545..1430e7d63c 100644
--- a/src/include/storage/large_object.h
+++ b/src/include/storage/large_object.h
@@ -8,14 +8,14 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/large_object.h,v 1.39 2008/01/01 19:45:59 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/large_object.h,v 1.40 2008/03/26 16:20:48 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
 #ifndef LARGE_OBJECT_H
 #define LARGE_OBJECT_H
 
-#include "utils/tqual.h"
+#include "utils/snapshot.h"
 
 
 /*----------
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index 26b27fa941..160b6c9670 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/procarray.h,v 1.20 2008/01/09 21:52:36 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/storage/procarray.h,v 1.21 2008/03/26 16:20:48 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -15,6 +15,7 @@
 #define PROCARRAY_H
 
 #include "storage/lock.h"
+#include "utils/snapshot.h"
 
 
 extern Size ProcArrayShmemSize(void);
@@ -25,6 +26,8 @@ extern void ProcArrayRemove(PGPROC *proc, TransactionId latestXid);
 extern void ProcArrayEndTransaction(PGPROC *proc, TransactionId latestXid);
 extern void ProcArrayClearTransaction(PGPROC *proc);
 
+extern Snapshot GetSnapshotData(Snapshot snapshot, bool serializable);
+
 extern bool TransactionIdIsInProgress(TransactionId xid);
 extern bool TransactionIdIsActive(TransactionId xid);
 extern TransactionId GetOldestXmin(bool allDbs, bool ignoreVacuum);
diff --git a/src/include/utils/snapmgmt.h b/src/include/utils/snapmgmt.h
new file mode 100644
index 0000000000..349523ea2e
--- /dev/null
+++ b/src/include/utils/snapmgmt.h
@@ -0,0 +1,33 @@
+/*-------------------------------------------------------------------------
+ *
+ * snapmgmt.h
+ *	  POSTGRES snapshot management definitions
+ *
+ * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * $PostgreSQL: pgsql/src/include/utils/snapmgmt.h,v 1.1 2008/03/26 16:20:48 alvherre Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef SNAPMGMT_H
+#define SNAPMGMT_H
+
+#include "utils/snapshot.h"
+
+
+extern PGDLLIMPORT Snapshot SerializableSnapshot;
+extern PGDLLIMPORT Snapshot LatestSnapshot;
+extern PGDLLIMPORT Snapshot ActiveSnapshot;
+
+extern TransactionId TransactionXmin;
+extern TransactionId RecentXmin;
+extern TransactionId RecentGlobalXmin;
+
+extern Snapshot GetTransactionSnapshot(void);
+extern Snapshot GetLatestSnapshot(void);
+extern Snapshot CopySnapshot(Snapshot snapshot);
+extern void FreeSnapshot(Snapshot snapshot);
+extern void FreeXactSnapshot(void);
+
+#endif /* SNAPMGMT_H */
diff --git a/src/include/utils/snapshot.h b/src/include/utils/snapshot.h
new file mode 100644
index 0000000000..7dca978ee9
--- /dev/null
+++ b/src/include/utils/snapshot.h
@@ -0,0 +1,62 @@
+/*-------------------------------------------------------------------------
+ *
+ * snapshot.h
+ *	  POSTGRES snapshot definition
+ *
+ * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * $PostgreSQL: pgsql/src/include/utils/snapshot.h,v 1.1 2008/03/26 16:20:48 alvherre Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef SNAPSHOT_H
+#define SNAPSHOT_H
+
+#include "access/htup.h"
+#include "storage/buf.h"
+
+
+typedef struct SnapshotData *Snapshot;
+
+#define InvalidSnapshot		((Snapshot) NULL)
+
+/*
+ * We use SnapshotData structures to represent both "regular" (MVCC)
+ * snapshots and "special" snapshots that have non-MVCC semantics.
+ * The specific semantics of a snapshot are encoded by the "satisfies"
+ * function.
+ */
+typedef bool (*SnapshotSatisfiesFunc) (HeapTupleHeader tuple,
+									   Snapshot snapshot, Buffer buffer);
+
+typedef struct SnapshotData
+{
+	SnapshotSatisfiesFunc satisfies;	/* tuple test function */
+
+	/*
+	 * The remaining fields are used only for MVCC snapshots, and are normally
+	 * just zeroes in special snapshots.  (But xmin and xmax are used
+	 * specially by HeapTupleSatisfiesDirty.)
+	 *
+	 * An MVCC snapshot can never see the effects of XIDs >= xmax. It can see
+	 * the effects of all older XIDs except those listed in the snapshot. xmin
+	 * is stored as an optimization to avoid needing to search the XID arrays
+	 * for most tuples.
+	 */
+	TransactionId xmin;			/* all XID < xmin are visible to me */
+	TransactionId xmax;			/* all XID >= xmax are invisible to me */
+	uint32		xcnt;			/* # of xact ids in xip[] */
+	TransactionId *xip;			/* array of xact IDs in progress */
+	/* note: all ids in xip[] satisfy xmin <= xip[i] < xmax */
+	int32		subxcnt;		/* # of xact ids in subxip[], -1 if overflow */
+	TransactionId *subxip;		/* array of subxact IDs in progress */
+
+	/*
+	 * note: all ids in subxip[] are >= xmin, but we don't bother filtering
+	 * out any that are >= xmax
+	 */
+	CommandId	curcid;			/* in my xact, CID < curcid are visible */
+} SnapshotData;
+
+#endif /* SNAPSHOT_H */
diff --git a/src/include/utils/tqual.h b/src/include/utils/tqual.h
index a0399bd331..c9e078369f 100644
--- a/src/include/utils/tqual.h
+++ b/src/include/utils/tqual.h
@@ -8,59 +8,16 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/utils/tqual.h,v 1.71 2008/01/01 19:45:59 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/utils/tqual.h,v 1.72 2008/03/26 16:20:48 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
 #ifndef TQUAL_H
 #define TQUAL_H
 
-#include "access/htup.h"
-#include "storage/buf.h"
+#include "utils/snapshot.h"
 
 
-/*
- * We use SnapshotData structures to represent both "regular" (MVCC)
- * snapshots and "special" snapshots that have non-MVCC semantics.
- * The specific semantics of a snapshot are encoded by the "satisfies"
- * function.
- */
-typedef struct SnapshotData *Snapshot;
-
-typedef bool (*SnapshotSatisfiesFunc) (HeapTupleHeader tuple,
-										   Snapshot snapshot, Buffer buffer);
-
-typedef struct SnapshotData
-{
-	SnapshotSatisfiesFunc satisfies;	/* tuple test function */
-
-	/*
-	 * The remaining fields are used only for MVCC snapshots, and are normally
-	 * just zeroes in special snapshots.  (But xmin and xmax are used
-	 * specially by HeapTupleSatisfiesDirty.)
-	 *
-	 * An MVCC snapshot can never see the effects of XIDs >= xmax. It can see
-	 * the effects of all older XIDs except those listed in the snapshot. xmin
-	 * is stored as an optimization to avoid needing to search the XID arrays
-	 * for most tuples.
-	 */
-	TransactionId xmin;			/* all XID < xmin are visible to me */
-	TransactionId xmax;			/* all XID >= xmax are invisible to me */
-	uint32		xcnt;			/* # of xact ids in xip[] */
-	TransactionId *xip;			/* array of xact IDs in progress */
-	/* note: all ids in xip[] satisfy xmin <= xip[i] < xmax */
-	int32		subxcnt;		/* # of xact ids in subxip[], -1 if overflow */
-	TransactionId *subxip;		/* array of subxact IDs in progress */
-
-	/*
-	 * note: all ids in subxip[] are >= xmin, but we don't bother filtering
-	 * out any that are >= xmax
-	 */
-	CommandId	curcid;			/* in my xact, CID < curcid are visible */
-} SnapshotData;
-
-#define InvalidSnapshot		((Snapshot) NULL)
-
 /* Static variables representing various special snapshot semantics */
 extern PGDLLIMPORT SnapshotData SnapshotNowData;
 extern PGDLLIMPORT SnapshotData SnapshotSelfData;
@@ -84,15 +41,6 @@ extern PGDLLIMPORT SnapshotData SnapshotToastData;
 #define IsMVCCSnapshot(snapshot)  \
 	((snapshot)->satisfies == HeapTupleSatisfiesMVCC)
 
-
-extern PGDLLIMPORT Snapshot SerializableSnapshot;
-extern PGDLLIMPORT Snapshot LatestSnapshot;
-extern PGDLLIMPORT Snapshot ActiveSnapshot;
-
-extern TransactionId TransactionXmin;
-extern TransactionId RecentXmin;
-extern TransactionId RecentGlobalXmin;
-
 /*
  * HeapTupleSatisfiesVisibility
  *		True iff heap tuple satisfies a time qual.
@@ -149,13 +97,4 @@ extern HTSV_Result HeapTupleSatisfiesVacuum(HeapTupleHeader tuple,
 extern void HeapTupleSetHintBits(HeapTupleHeader tuple, Buffer buffer,
 					 uint16 infomask, TransactionId xid);
 
-extern Snapshot GetTransactionSnapshot(void);
-extern Snapshot GetLatestSnapshot(void);
-extern Snapshot CopySnapshot(Snapshot snapshot);
-extern void FreeSnapshot(Snapshot snapshot);
-extern void FreeXactSnapshot(void);
-
-/* in procarray.c; declared here to avoid including tqual.h in procarray.h: */
-extern Snapshot GetSnapshotData(Snapshot snapshot, bool serializable);
-
 #endif   /* TQUAL_H */