[lttng-dev] CTF viewing with timeless events

[Thibault, Daniel]

Date: Wed, 22 May 2013 10:04:41 -0400
From: Matthew Khouzam <matthew.khouzam at ericsson.com>

I was given an interesting corner case and want to explain how I believe it should be handled.

You are given a trace with no timestamps, and n channels.  How do you display the events?

I propose (and have implemented) that we have a secondary fallback key to sort events.
Right now, I believe babeltrace will sort by timestamp and that's it.
The eclipse viewer sorts by timestamp and if timestamps match, it sorts by stream file name.
In one given trace, stream file names are unique like (channel_0).

This means if you have 5 stream files with five events each, it will always output as
"stream1: e1-e2-e3-e4-e5 stream2: e1-e2-e3-e4-e5 stream3: e1-e2-e3-e4-e5 stream4: e1-e2-e3-e4-e5 stream5: e1-e2-e3-e4-e5"

This should avoid confusion from a reader's perspective.

Comments?
------------------------------
   At first I thought this had to be wrong because trace events always have a time-stamp, but then I reread the CTF spec and, indeed, *all* of the event packet context fields are optional, so it is possible to have a timeless trace.  In which case I agree with this design.

Daniel U. Thibault
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