Pointed out by Andres Freund
/*
* Oldest LSN that the client has acked receipt for. This is used as the
* start_lsn point in case the client doesn't specify one, and also as a
- * safety measure to back off in case the client specifies a start_lsn
- * that's further in the future than this value.
+ * safety measure to jump forwards in case the client specifies a
+ * start_lsn that's further in the past than this value.
*/
XLogRecPtr confirmed_flush;