Improve comment for GetStableLatestTransactionId().

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 5ae46dee9b5168afc5d2e6382d10fb50a878a134..49c14cb64c02a39cac4e6d4dfbcdeb015bcc2a53 100644 (file)
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -393,8 +393,10 @@ GetCurrentTransactionIdIfAny(void)
 /*
  *     GetStableLatestTransactionId
  *
- * Get the XID once and then return same value for rest of transaction.
- * Acts as a useful reference point for maintenance tasks.
+ * Get the transaction's XID if it has one, else read the next-to-be-assigned
+ * XID.  Once we have a value, return that same value for the remainder of the
+ * current transaction.  This is meant to provide the reference point for the
+ * age(xid) function, but might be useful for other maintenance tasks as well.
  */
 TransactionId
 GetStableLatestTransactionId(void)