Avoid xid error from age() function when run on Hot Standby

diff --git a/src/backend/utils/adt/xid.c b/src/backend/utils/adt/xid.c
index 1829b8242d29ce884868347958378803a0da259d..eeda081ad18adb1f523f69f6cc1086e8fba7da3a 100644 (file)
--- a/src/backend/utils/adt/xid.c
+++ b/src/backend/utils/adt/xid.c
@@ -93,7 +93,10 @@ Datum
 xid_age(PG_FUNCTION_ARGS)
 {
    TransactionId xid = PG_GETARG_TRANSACTIONID(0);
-   TransactionId now = GetTopTransactionId();
+   TransactionId now = GetTopTransactionIdIfAny();
+
+   if (!TransactionIdIsValid(now))
+       now = ReadNewTransactionId();
 
    /* Permanent XIDs are always infinitely old */
    if (!TransactionIdIsNormal(xid))