show # messages, use msgpack to compress json

interface/src/system/LogEventForm.tsx

@@ -5,6 +5,8 @@ import {
   SelectValidator
 } from 'react-material-ui-form-validator';
 
+import { Typography } from '@material-ui/core';
+
 import MenuItem from '@material-ui/core/MenuItem';
 
 import {
@@ -79,6 +81,9 @@ class LogEventForm extends Component<LogEventFormProps> {
           <MenuItem value={7}>DEBUG</MenuItem>
           <MenuItem value={8}>TRACE</MenuItem>
         </SelectValidator>
+        <Typography color="primary" variant="body2">
+          <i>Only the last {data.max_messages} messages are shown</i>
+        </Typography>
       </ValidatorForm>
     );
   }