doc/live-reading-howto.txt

   1 LTTng Live trace reading how-to
   2
   3 Julien Desfossez
   4 September 27th, 2013
   5
   6 This document presents a summary on how to use the live trace reading feature
   7 introduced in LTTng 2.4. For the details about the protocol, please refer to
   8 the live-reading-protocol.txt document.
   9
  10 Live trace reading refers to the feature of reading the trace while it is being
  11 recorded. In order to do that, the trace must be streamed a relay even if the
  12 viewer is running on the same machine as the tracer.
  13
  14 So, the first thing to do is to start a lttng-relayd process. It can be
  15 anywhere on the network (including localhost) as long as the sessiond/consumerd
  16 and the viewer can communicate with it over TCP/IP.
  17
  18 $ lttng-relayd -d
  19
  20 Then, we can create a session configured for streaming with the new --live
  21 parameter.
  22
  23 $ lttng create --live 1000000 -U net://localhost
  24
  25 The --live parameter activates a session-wide timer (usec) that is responsible
  26 for checking at a user-defined rate if new data is available. If there is new
  27 data, it is flushed automatically, otherwise a beacon is sent to the relayd to
  28 inform it that the stream is currently empty and the viewer can ignore this
  29 stream up to a certain point in time.
  30
  31 Once the session is created, the user can activate events as usual.
  32
  33 In order to view the live trace, the viewer must implement the live-reading
  34 protocol. As of now, Babeltrace[1] and LTTngTop[2] implement the protocol.
  35
  36 [1] git://git.efficios.com/babeltrace.git
  37 [2] git://git.lttng.org/lttngtop.git