lnd: reduce max limit when querying for payments

Author: ziggie1984

payments/db/query.go

@@ -1,5 +1,11 @@
 package paymentsdb
 
+const (
+	// DefaultMaxPayments is the default maximum number of payments returned
+	// in the payments query pagination.
+	DefaultMaxPayments = 100
+)
+
 // Query represents a query to the payments database starting or ending
 // at a certain offset index. The number of retrieved records can be limited.
 type Query struct {

rpcserver.go

@@ -7523,10 +7523,15 @@ func (r *rpcServer) ListPayments(ctx context.Context,
 		CreationDateEnd:   int64(req.CreationDateEnd),
 	}
 
-	// If the maximum number of payments wasn't specified, then we'll
-	// default to return the maximal number of payments representable.
+	// If the maximum number of payments wasn't specified, we default to
+	// a reasonable number to prevent resource exhaustion. All of the
+	// payments are fetched into memory. Moreover we don't want our daemon
+	// to remain stable and do other stuff rather than serving payments.
+	//
+	// TODO(ziggie): Choose a more specific default value when results of
+	// performance testing are available.
 	if req.MaxPayments == 0 {
-		query.MaxPayments = math.MaxUint64
+		query.MaxPayments = paymentsdb.DefaultMaxPayments
 	}
 
 	paymentsQuerySlice, err := r.server.paymentsDB.QueryPayments(