trigger: implement trigger naming
[lttng-tools.git] / 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
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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
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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.
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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
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