[ltt-dev] Flight-recording mode

[Gerlando Falauto]

On 10/28/2011 10:24 AM, Mathieu Desnoyers wrote:
> * Gerlando Falauto (gerlando.falauto at keymile.com) wrote:
>> On 10/28/2011 09:39 AM, Mathieu Desnoyers wrote:
>>> * Gerlando Falauto (gerlando.falauto at keymile.com) wrote:
>> ...
>>>> How can I make sure that only the latest N seconds of traces will be
>>>> saved? The answer should be flight-recording mode, but how do I really
>>>> do it?
>>>
>>> I discussed this with David this morning, and we'll need to enhance
>>> ltt-sessiond in lttng-tools to ensure it does not send the streams to
>>> the consumer daemon upon trace start for overwrite mode channels, but
>>> just on trace stop. This is lacking currently.
>>
>> OK, thanks!
>> Does that also apply to LTTng 0.x (since I got the same impression)?
>>
>> For 0.x I came up with the idea of killing lttd but I don't know if
>> a) it's a good idea;
>> b) it would do the trick
>
> for 0.x it should all just work (TM) ;)

Yeah, it sorta-kinda-most-of-the-times-almost works (R). :-)

I am having problems seeing those traces on LTTv though.
I had to come up with a workaround by patching LLTv and doing some weird 
stuff after loading the trace in order to have LTTv not crash.

And also, half the times I cannot see some of the process names (of 
course, the ones I am really interested in). Is there any explanation 
for this?

> by specifying flight recorder mode, lttctl is supposed to launch lttd
> only on non-overwrite mode buffers (metadata) first, and only upon trace
> teardown does it hook lttd on the flight recorder buffers.

If you don't mind me asking, what's the point of having lttd running in 
background in that case (all channels in flight recorder mode)?

Thanks!
Gerlando