1 files changed, 48 insertions, 3 deletions

diff --git a/src/include/access/transam.h b/src/include/access/transam.h
index 78997e533e7..6a919084c8f 100644
--- a/src/include/access/transam.h
+++ b/src/include/access/transam.h
@@ -44,6 +44,32 @@
 #define TransactionIdStore(xid, dest)	(*(dest) = (xid))
 #define StoreInvalidTransactionId(dest) (*(dest) = InvalidTransactionId)
 
+#define EpochFromFullTransactionId(x)	((uint32) ((x).value >> 32))
+#define XidFromFullTransactionId(x)		((uint32) (x).value)
+#define U64FromFullTransactionId(x)		((x).value)
+#define FullTransactionIdPrecedes(a, b)	((a).value < (b).value)
+#define FullTransactionIdIsValid(x)		TransactionIdIsValid(XidFromFullTransactionId(x))
+
+/*
+ * A 64 bit value that contains an epoch and a TransactionId.  This is
+ * wrapped in a struct to prevent implicit conversion to/from TransactionId.
+ * Not all values represent valid normal XIDs.
+ */
+typedef struct FullTransactionId
+{
+	uint64		value;
+} FullTransactionId;
+
+static inline FullTransactionId
+FullTransactionIdFromEpochAndXid(uint32 epoch, TransactionId xid)
+{
+	FullTransactionId result;
+
+	result.value = ((uint64) epoch) << 32 | xid;
+
+	return result;
+}
+
 /* advance a transaction ID variable, handling wraparound correctly */
 #define TransactionIdAdvance(dest)	\
 	do { \
@@ -52,6 +78,15 @@
 			(dest) = FirstNormalTransactionId; \
 	} while(0)
 
+/* advance a FullTransactionId variable, stepping over special XIDs */
+static inline void
+FullTransactionIdAdvance(FullTransactionId *dest)
+{
+	dest->value++;
+	while (XidFromFullTransactionId(*dest) < FirstNormalTransactionId)
+		dest->value++;
+}
+
 /* back up a transaction ID variable, handling wraparound correctly */
 #define TransactionIdRetreat(dest)	\
 	do { \
@@ -125,12 +160,12 @@ typedef struct VariableCacheData
 	/*
 	 * These fields are protected by XidGenLock.
 	 */
-	TransactionId nextXid;		/* next XID to assign */
+	FullTransactionId nextFullXid;	/* next full XID to assign */
 
 	TransactionId oldestXid;	/* cluster-wide minimum datfrozenxid */
 	TransactionId xidVacLimit;	/* start forcing autovacuums here */
 	TransactionId xidWarnLimit; /* start complaining here */
-	TransactionId xidStopLimit; /* refuse to advance nextXid beyond here */
+	TransactionId xidStopLimit; /* refuse to advance nextFullXid beyond here */
 	TransactionId xidWrapLimit; /* where the world ends */
 	Oid			oldestXidDB;	/* database with minimum datfrozenxid */
 
@@ -187,11 +222,21 @@ extern XLogRecPtr TransactionIdGetCommitLSN(TransactionId xid);
 
 /* in transam/varsup.c */
 extern TransactionId GetNewTransactionId(bool isSubXact);
-extern TransactionId ReadNewTransactionId(void);
+extern void AdvanceNextFullTransactionIdPastXid(TransactionId xid);
+extern FullTransactionId ReadNextFullTransactionId(void);
 extern void SetTransactionIdLimit(TransactionId oldest_datfrozenxid,
 					  Oid oldest_datoid);
 extern void AdvanceOldestClogXid(TransactionId oldest_datfrozenxid);
 extern bool ForceTransactionIdLimitUpdate(void);
 extern Oid	GetNewObjectId(void);
 
+/*
+ * For callers that just need the XID part of the next transaction ID.
+ */
+static inline TransactionId
+ReadNewTransactionId(void)
+{
+	return XidFromFullTransactionId(ReadNextFullTransactionId());
+}
+
 #endif							/* TRAMSAM_H */