Thread: A fastpath for TransactionIdIsCurrentTransactionId

In my recent work,  I want to check if the xmin for all the tuples is CurrentTransactioniId,

then I found we can improve the  fastpath for TransactionIdIsCurrentTransactionId 

like below,  would it be safe?  This would be helpful if we have lots of sub transactionId. 

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 3596a7d7345..e4721a6cb39 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -935,8 +935,12 @@ TransactionIdIsCurrentTransactionId(TransactionId xid)
         * Likewise, InvalidTransactionId and FrozenTransactionId are certainly
         * not my transaction ID, so we can just return "false" immediately for
         * any non-normal XID.
+        *
+        * And any Transaction IDs precede TransactionXmin are certainly not
+        * my transaction ID as well.
         */
-       if (!TransactionIdIsNormal(xid))
+
+       if (TransactionIdPrecedes(xid, TransactionXmin))
                return false;

        if (TransactionIdEquals(xid, GetTopTransactionIdIfAny()))
--