snapshotnow_consistent.v4.patch

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 5f6ac2e..8c6d6a1 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -1201,6 +1201,8 @@ heap_beginscan_internal(Relation relation, Snapshot snapshot,
 	 */
 	scan->rs_pageatatime = IsMVCCSnapshot(snapshot);
 
+	InitSnapshotNowIfNeeded(snapshot);
+
 	/*
 	 * For a seqscan in a serializable transaction, acquire a predicate lock
 	 * on the entire relation. This is required not only to lock all the
@@ -1680,6 +1682,8 @@ heap_get_latest_tid(Relation relation,
 	if (!ItemPointerIsValid(tid))
 		return;
 
+	InitSnapshotNowIfNeeded(snapshot);
+
 	/*
 	 * Since this can be called with user-supplied TID, don't trust the input
 	 * too much.  (RelationGetNumberOfBlocks is an expensive check, so we
diff --git a/src/backend/access/index/indexam.c b/src/backend/access/index/indexam.c
index 16ac4e1..4e03cb5 100644
--- a/src/backend/access/index/indexam.c
+++ b/src/backend/access/index/indexam.c
@@ -292,6 +292,8 @@ index_beginscan_internal(Relation indexRelation,
 	 */
 	RelationIncrementReferenceCount(indexRelation);
 
+	InitSnapshotNowIfNeeded(snapshot);
+
 	/*
 	 * Tell the AM to open a scan.
 	 */
diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c
index 5aebbd1..61090be 100644
--- a/src/backend/utils/time/snapmgr.c
+++ b/src/backend/utils/time/snapmgr.c
@@ -206,6 +206,19 @@ GetLatestSnapshot(void)
 }
 
 /*
+ * InitSnapshotNowIfNeeded
+ *		If passed snapshot is SnapshotNow then refresh it with latest info.
+ */
+void
+InitSnapshotNowIfNeeded(Snapshot snap)
+{
+	if (!IsSnapshotNow(snap))
+		return;
+
+	snap = GetSnapshotData(&SnapshotNowData);
+}
+
+/*
  * SnapshotSetCommandId
  *		Propagate CommandCounterIncrement into the static snapshots, if set
  */
diff --git a/src/backend/utils/time/tqual.c b/src/backend/utils/time/tqual.c
index 31791a7..61edafa 100644
--- a/src/backend/utils/time/tqual.c
+++ b/src/backend/utils/time/tqual.c
@@ -67,7 +67,7 @@
 
 
 /* Static variables representing various special snapshot semantics */
-SnapshotData SnapshotNowData = {HeapTupleSatisfiesNow};
+SnapshotData SnapshotNowData = {HeapTupleSatisfiesMVCC};
 SnapshotData SnapshotSelfData = {HeapTupleSatisfiesSelf};
 SnapshotData SnapshotAnyData = {HeapTupleSatisfiesAny};
 SnapshotData SnapshotToastData = {HeapTupleSatisfiesToast};
@@ -293,6 +293,7 @@ HeapTupleSatisfiesSelf(HeapTupleHeader tuple, Snapshot snapshot, Buffer buffer)
 	return false;
 }
 
+#ifdef RECENTLY_DEAD_CODE
 /*
  * HeapTupleSatisfiesNow
  *		True iff heap tuple is valid "now".
@@ -474,6 +475,7 @@ HeapTupleSatisfiesNow(HeapTupleHeader tuple, Snapshot snapshot, Buffer buffer)
 				HeapTupleHeaderGetXmax(tuple));
 	return false;
 }
+#endif
 
 /*
  * HeapTupleSatisfiesAny
diff --git a/src/include/utils/snapmgr.h b/src/include/utils/snapmgr.h
index f195981..a30fb9f 100644
--- a/src/include/utils/snapmgr.h
+++ b/src/include/utils/snapmgr.h
@@ -24,6 +24,7 @@ extern TransactionId RecentGlobalXmin;
 
 extern Snapshot GetTransactionSnapshot(void);
 extern Snapshot GetLatestSnapshot(void);
+extern void InitSnapshotNowIfNeeded(Snapshot snap);
 extern void SnapshotSetCommandId(CommandId curcid);
 
 extern void PushActiveSnapshot(Snapshot snapshot);
diff --git a/src/include/utils/tqual.h b/src/include/utils/tqual.h
index 0f8a7f8..760fc3f 100644
--- a/src/include/utils/tqual.h
+++ b/src/include/utils/tqual.h
@@ -40,6 +40,8 @@ extern PGDLLIMPORT SnapshotData SnapshotToastData;
 /* This macro encodes the knowledge of which snapshots are MVCC-safe */
 #define IsMVCCSnapshot(snapshot)  \
 	((snapshot)->satisfies == HeapTupleSatisfiesMVCC)
+#define IsSnapshotNow(snapshot)  \
+	((snapshot) == (&SnapshotNowData))
 
 /*
  * HeapTupleSatisfiesVisibility