[lttng-dev] Have live session and rotation together

[Mathieu Desnoyers]

----- On Apr 22, 2020, at 2:18 PM, Sergei Dyshel qyron.private at gmail.com wrote:

> Thanks! I really missed this feature somehow.
> 
> However I see that passing 0 as "tracefile size" will remove size
> limitation. Is it possible to disable CTF trace writing altogether?

No, because the relay daemon uses the on-disk files as intermediate
storage between the receiving end and the part interacting with live
viewers.

Note that https://bugs.lttng.org/issues/1182 tracks a known issue
where the relay daemon mishandles tracefile-count == 0 and tracefile-size != 0.
It has not been a priority to fix this issue so far.

Thanks,

Mathieu


> --
> Regards,
> Sergei Dyshel
> 
> On Wed, Apr 22, 2020 at 2:15 AM Mathieu Desnoyers
> <mathieu.desnoyers at efficios.com> wrote:
>>
>> ----- On Apr 21, 2020, at 5:37 PM, Sergei Dyshel qyron.private at gmail.com wrote:
>>
>> [...]
>> >
>> >> Considering that there are few compelling use-cases for using both
>> >> features together, and no customer have expressed interest in this,
>> >> it is not part of our roadmap.
>> >
>> > Here is my case: I'm using LTTNG for continuous tracing during the
>> > whole system timeline,
>> > generating pretty big volume of traces.
>> >
>> > I'm using live and session and Babeltrace2 plugin which converts
>> > processes these traces,
>> > converts them to text and stores them
>> > in some text file to which I apply "logrotate" so that old traces are
>> > archived when needed.
>> >
>> > However, as I see, "lttng-relayd" also writes binary traces in CTF
>> > from to some directory, never discarding old traces. So assuming
>> > system long runtime this directory is going to eat all the free space
>> > sometime?! Rotation would allow me to discard old archives just as
>> > "logrotate" does. How else can I discard old CTF files?
>>
>> The feature you need is called "tracefile rotation", with the channel
>> attributes "tracefile count" and "tracefile size". It was implemented at
>> the same time as the live mode for exactly the purpose you describe.
>>
>> See https://lttng.org/docs/#doc-tracefile-rotation for more information.
>>
>> Thanks,
>>
>> Mathieu
>>
>> --
>> Mathieu Desnoyers
>> EfficiOS Inc.
> > http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com