Hi Michael
Live trace reading within Trace Compass is supported but it is still
rudimentary and needs some improvements. When implementing the
support for live trace reading in Trace Compass the use cases were
not fully clear. We still need some user feedback to improve upon
the current implementation. If you have any suggestions please let
us know (on the mailing list or on bugzilla). Due to other
priorities we are not currently working on this. However, we would
be glad to review any contributions and improvements.
What is currently possible
----------------------------------
It is possible to create a live session using the LTTng Control view
(as you already realized). One thing to know is that the
lttng-relayd and Trace Compass has to run on the same host. It is
not possible to use a lttng-relayd running on a separate node for
live trace reading.
After configuring the live session from Trace Compass (using the
Control view) you can import the trace from the control view. This
will link the trace into the tracing project where you can open the
trace. Trace Compass will discover new events using the lttng-relayd
and the following views will be updated when new data arrives:
- Events table
- Histogram view
- Statistics view
- Views that are using a state system are updated (e.g. Control Flow
view)
Note that Trace Compass will read the data from the disk written by
lttng-relayd. It is not requesting the trace events directly from
the lttng-relayd. That's why lttng-relayd and Trace Compass have to
run at the same host.
The last time I tried it I realized some issues. I used with LTTng
2.7 and Trace Compass 1.2 at that time. I opened 2 bugs to track the
issues and improvements [1] and [2]. Note that traced system,
lttng-relayd and Trace Compass were running at the same machine in
my test.
Known limitations
-----------------------
- Tracing the system (kernel and/UST) on the same node than
lttng-relayd and Trace Compass is performant
- Live updating of several views is very slow
- It's only possible to stream one trace at a time, e.g. just LTTng
Kernel or one UST application with per-uid buffers for tracing.
Best Regards
Bernd
[1] https://bugs.eclipse.org/bugs/show_bug.cgi?id=486728
[2] https://bugs.eclipse.org/bugs/show_bug.cgi?id=486727
On 03/04/2016 11:39 AM, Michael Steppe
wrote:
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