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Re: [tracecompass-dev] uuid of the trace clock

Hi Geneviève,
thanks for yout reply. I meant by looking at the tracecompass GUI. 
I was looking for a way to determine traces belonging together 
when creating an experiment. 
Thanks for the tip with the trace properties, that definitly works 
for me! Nevertheless, how do you feel about additionally displaying 
the host ID in the "Select Traces" dialog? Like that traces would be 
attributable at a glance.


Sent: Mondy, 13. November 2017 at 15:30
From: "Geneviève Bastien" <gbastien@xxxxxxxxxxxx>
To: tracecompass-dev@xxxxxxxxxxx
Subject: Re: [tracecompass-dev] uuid of the trace clock
Hi Chris,

On 2017-11-13 04:01 AM, Mansky Christian wrote:
> Dear tracecompassers.
> I have a question regarding the uuid of the trace-clock (in the
> metadata). I only did a very quick research of the following, so
> please correct me if I'm wrong. However, it is my understanding that
> Lttng takes the boot_id (in /proc/sys/kernel/random) as the uuid of
> the clock. Since Lttng uses the CLOCK_MONOTONIC this makes sense, as
> every combination of the monotonic timestamp and the boot_id creates a
> unique timestamp.
> If I now have a tracing project with multiple traces from different
> boot-ups, I would like to identify traces that belong together (for
> creating an experiment). Uuid-wise; hence, from the same bootup and
> timestamp-wise; meaning overlapping traces). Is there a quick way to
> do this?
You mean programmatically or a for a user looking at the Trace Compass GUI?

The former is the easiest. As you said, traces from the same bootup have
the same clock-id. That's why we use the clock-id as the host ID for CTF
traces (using hostname have more chances of name clashes, like a few VMs
named ubuntu, but clock-id is unique per machine). That's how we know a
UST and kernel traces go together for instance. Then we use
trace1.getHostId() in code to identify the host. Most analyses in Trace
Compass are host-aware.

In the Trace Compass GUI, if you select an opened CTF trace and look at
the Properties view, you will see under the "Trace Properties", a
property called "Host ID", which corresponds to the clock id.

I hope this helps,
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