contents/understanding-lttng/core-concepts/channel/channel-timers.md

   1 ---
   2 id: channel-switch-timer
   3 ---
   4
   5 The _switch timer_ period is another important configurable feature of
   6 channels to ensure periodic sub-buffer flushing.
   7
   8 When the _switch timer_ fires, a sub-buffer switch happens. This timer
   9 may be used to ensure that event data is consumed and committed to
  10 trace files periodically in case of a low event throughput:
  11
  12 <script type="text/javascript">
  13     document.write('<div class="img img-50" id="docsvg-channel-switch-timer"></div>');
  14
  15     $(document).ready(function() {
  16         var doc = SVG('docsvg-channel-switch-timer');
  17
  18         doc.viewbox(0, 0, 2, 2);
  19
  20         var div = 4;
  21         var evDur = 1000;
  22         var rb = rbBuildStd(doc, div, 0.97);
  23         var switchText = doc.text('Switch!');
  24
  25         switchText.font({
  26             'size': 0.1,
  27             'weight': 'bold'
  28         });
  29         switchText.center(1, 1);
  30         switchText.attr({
  31             'opacity': 0,
  32             'fill': '#b02b2c'
  33         });
  34
  35         var curSubBuf = 0;
  36         var totalEvents = 0;
  37         var onEventAdded = function() {
  38             totalEvents++;
  39
  40             var curSubBufEvCount = rb.getSubBufEvCount(curSubBuf % div);
  41
  42             if (totalEvents >= 4) {
  43                 // switch timer fires
  44                 switchText.attr({
  45                     'opacity': 1
  46                 });
  47                 switchText.animate(500, '<>', 1000).attr({
  48                     'opacity': 0
  49                 });
  50                 rb.markSubBuf(curSubBuf % div, 'full');
  51
  52                 var lastFullSubBuf = curSubBuf;
  53
  54                 setTimeout(function() {
  55                     rb.consumeSubBuf(lastFullSubBuf % div);
  56                 }, 3000);
  57                 totalEvents = 0;
  58                 curSubBuf++;
  59                 rb.markSubBuf(curSubBuf % div, 'cur');
  60             }
  61
  62             rb.addEvent(curSubBuf % div, evDur, onEventAdded);
  63         };
  64
  65         rb.addEvent(0, evDur, onEventAdded);
  66         rb.markSubBuf(0, 'cur');
  67
  68         rb.getGroup().move(1, 1);
  69     });
  70 </script>
  71
  72 <noscript>
  73     <div class="err">
  74         <p>
  75             <span class="t">Oops!</span>JavaScript must be enabled in
  76             order to view animations.
  77         </p>
  78     </div>
  79 </noscript>
  80
  81 It's also convenient when big sub-buffers are used to cope with
  82 sporadic high event throughput, even if the throughput is normally
  83 lower.