From 493f72606b463a75ae4e2ee4e64d829e7f56066d Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 11 Sep 2004 18:28:34 +0000
Subject: [PATCH] Renumber SnapshotNow and the other special snapshot codes so
that ((Snapshot) NULL) can no longer be confused with a valid snapshot, as
per my recent suggestion. Define a macro InvalidSnapshot for 0. Use
InvalidSnapshot instead of SnapshotAny as the do-nothing special case for
heap_update and heap_delete crosschecks; this seems a little cleaner even
though the behavior is really the same.
---
src/backend/access/heap/heapam.c | 20 +++++++++++---------
src/backend/commands/async.c | 4 ++--
src/backend/executor/execMain.c | 4 ++--
src/backend/executor/execUtils.c | 4 ++--
src/include/utils/tqual.h | 26 +++++++++++++++++++++-----
5 files changed, 38 insertions(+), 20 deletions(-)
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 6dd0c357fbb..e5284d0b8c1 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.173 2004/08/29 05:06:40 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.174 2004/09/11 18:28:32 tgl Exp $
*
*
* INTERFACE ROUTINES
@@ -1262,7 +1262,7 @@ simple_heap_insert(Relation relation, HeapTuple tup)
* tid - TID of tuple to be deleted
* ctid - output parameter, used only for failure case (see below)
* cid - delete command ID to use in verifying tuple visibility
- * crosscheck - if not SnapshotAny, also check tuple against this
+ * crosscheck - if not InvalidSnapshot, also check tuple against this
* wait - true if should wait for any conflicting update to commit/abort
*
* Normal, successful return value is HeapTupleMayBeUpdated, which
@@ -1274,7 +1274,8 @@ simple_heap_insert(Relation relation, HeapTuple tup)
*/
int
heap_delete(Relation relation, ItemPointer tid,
- ItemPointer ctid, CommandId cid, Snapshot crosscheck, bool wait)
+ ItemPointer ctid, CommandId cid,
+ Snapshot crosscheck, bool wait)
{
ItemId lp;
HeapTupleData tp;
@@ -1339,7 +1340,7 @@ l1:
result = HeapTupleUpdated;
}
- if (crosscheck != SnapshotAny && result == HeapTupleMayBeUpdated)
+ if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
{
/* Perform additional check for serializable RI updates */
if (!HeapTupleSatisfiesSnapshot(tp.t_data, crosscheck))
@@ -1443,7 +1444,7 @@ simple_heap_delete(Relation relation, ItemPointer tid)
result = heap_delete(relation, tid,
&ctid,
- GetCurrentCommandId(), SnapshotAny,
+ GetCurrentCommandId(), InvalidSnapshot,
true /* wait for commit */ );
switch (result)
{
@@ -1477,7 +1478,7 @@ simple_heap_delete(Relation relation, ItemPointer tid)
* newtup - newly constructed tuple data to store
* ctid - output parameter, used only for failure case (see below)
* cid - update command ID to use in verifying old tuple visibility
- * crosscheck - if not SnapshotAny, also check old tuple against this
+ * crosscheck - if not InvalidSnapshot, also check old tuple against this
* wait - true if should wait for any conflicting update to commit/abort
*
* Normal, successful return value is HeapTupleMayBeUpdated, which
@@ -1491,7 +1492,8 @@ simple_heap_delete(Relation relation, ItemPointer tid)
*/
int
heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
- ItemPointer ctid, CommandId cid, Snapshot crosscheck, bool wait)
+ ItemPointer ctid, CommandId cid,
+ Snapshot crosscheck, bool wait)
{
ItemId lp;
HeapTupleData oldtup;
@@ -1566,7 +1568,7 @@ l2:
result = HeapTupleUpdated;
}
- if (crosscheck != SnapshotAny && result == HeapTupleMayBeUpdated)
+ if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
{
/* Perform additional check for serializable RI updates */
if (!HeapTupleSatisfiesSnapshot(oldtup.t_data, crosscheck))
@@ -1804,7 +1806,7 @@ simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
result = heap_update(relation, otid, tup,
&ctid,
- GetCurrentCommandId(), SnapshotAny,
+ GetCurrentCommandId(), InvalidSnapshot,
true /* wait for commit */ );
switch (result)
{
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index f25b8570455..c964f8d9fa7 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.116 2004/09/06 23:32:54 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.117 2004/09/11 18:28:33 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -544,7 +544,7 @@ AtCommit_Notify(void)
*/
result = heap_update(lRel, &lTuple->t_self, rTuple,
&ctid,
- GetCurrentCommandId(), SnapshotAny,
+ GetCurrentCommandId(), InvalidSnapshot,
false /* no wait for commit */ );
switch (result)
{
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index d77bc7054a3..b009e73e105 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -26,7 +26,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.236 2004/08/29 05:06:42 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.237 2004/09/11 18:28:34 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -176,7 +176,7 @@ ExecutorStart(QueryDesc *queryDesc, bool useCurrentSnapshot, bool explainOnly)
{
/* normal query --- use query snapshot, no crosscheck */
estate->es_snapshot = CopyQuerySnapshot();
- estate->es_crosscheck_snapshot = SnapshotAny;
+ estate->es_crosscheck_snapshot = InvalidSnapshot;
}
/*
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 79ab787b07a..a1736766b26 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/executor/execUtils.c,v 1.114 2004/08/29 05:06:42 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/executor/execUtils.c,v 1.115 2004/09/11 18:28:34 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -179,7 +179,7 @@ CreateExecutorState(void)
*/
estate->es_direction = ForwardScanDirection;
estate->es_snapshot = SnapshotNow;
- estate->es_crosscheck_snapshot = SnapshotAny; /* means no crosscheck */
+ estate->es_crosscheck_snapshot = InvalidSnapshot; /* no crosscheck */
estate->es_range_table = NIL;
estate->es_result_relations = NULL;
diff --git a/src/include/utils/tqual.h b/src/include/utils/tqual.h
index e378e444da1..627bcaf75a1 100644
--- a/src/include/utils/tqual.h
+++ b/src/include/utils/tqual.h
@@ -8,7 +8,7 @@
* Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/include/utils/tqual.h,v 1.50 2004/08/29 04:13:11 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/utils/tqual.h,v 1.51 2004/09/11 18:28:34 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -19,6 +19,20 @@
#include "access/xact.h"
+/*
+ * "Regular" snapshots are pointers to a SnapshotData structure.
+ *
+ * We also have some "special" snapshot values that have fixed meanings
+ * and don't need any backing SnapshotData. These are encoded by small
+ * integer values, which of course is a gross violation of ANSI C, but
+ * it works fine on all known platforms.
+ *
+ * SnapshotDirty is an even more special case: its semantics are fixed,
+ * but there is a backing SnapshotData struct for it. That struct is
+ * actually used as *output* data from tqual.c, not input into it.
+ * (But hey, SnapshotDirty ought to have a dirty implementation, no? ;-))
+ */
+
typedef struct SnapshotData
{
TransactionId xmin; /* XID < xmin are visible to me */
@@ -32,10 +46,12 @@ typedef struct SnapshotData
typedef SnapshotData *Snapshot;
-#define SnapshotNow ((Snapshot) 0x0)
-#define SnapshotSelf ((Snapshot) 0x1)
-#define SnapshotAny ((Snapshot) 0x2)
-#define SnapshotToast ((Snapshot) 0x3)
+/* Special snapshot values: */
+#define InvalidSnapshot ((Snapshot) 0x0) /* same as NULL */
+#define SnapshotNow ((Snapshot) 0x1)
+#define SnapshotSelf ((Snapshot) 0x2)
+#define SnapshotAny ((Snapshot) 0x3)
+#define SnapshotToast ((Snapshot) 0x4)
extern DLLIMPORT Snapshot SnapshotDirty;
extern DLLIMPORT Snapshot QuerySnapshot;
--
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