[lttng-dev] A question on protocols

[Jonathan Rajotte-Julien]

Hi Patrick,

> The security between consumerd and relayd isn't an issue as we'd be forced
> to keep both on the device. This because we have no way of transporting the
> consumerd <-> relayd communication over the HTTP proxy, which is our only
> choice. We have already talked to the team in charge of the network paths.

In that case using lttng-relayd yield no advantage unless you are able to have
a device running only lttng-relayd and gathering data from other devices and
then sending the data via http.


> 
> The relayd side have to be on the device. The device has very limited
> amounts of free flash. Even if there were flash available it would wear
> down the flash faster than what we'd like.

Not sure I follow here. The whole point of lttng-relayd is to be off the device
being traced and to relay trace data using network only (skipping disk).

> A RAM-based disc might have been a solution if we would have had any
> mentionable amounts of RAM to spare for this. Unfortunately we don't have
> that.

In all cases you will need some RAM somewhere if using LTTng (and I think any
other monitoring/tracing tools) since we need to allocate tracing buffer.

> >
> > Keep in mind that trace production is normally much more quicker than trace
> > reading/analysis. A buffering scheme is mostly always necessary.
> >
> 
> Very valid point, I'll for sure keep that in mind.
> 
> This speaks strongly against replacing relayd with something homebrewed, as
> was the original plan. We'd probably not be able to shuffle the data fast
> enough over the network to keep up with the pace.

If you are unable to "reserve" RAM/network bandwidth and/or use FLASH this is
slowly becoming a "you can't have your cake and eat it too" situation. This must
be frustrating...

> >
> > You can also use the --trace-file-size and --trace-file-count to limit the
> > disk
> > footprint of each live session. Make sure to have enough buffer for live
> > reading if still using live.
> >
> 
> This isn't an option as our disc is flash based and we'd like to limit the
> wear due to collecting metrics.

I was under the impression that the lttng-relayd process was on another device.
I misunderstood the situation.

Cheers

-- 
Jonathan Rajotte-Julien
EfficiOS