[lttng-dev] LTTng Tools 2.1 streaming commands

David Goulet dgoulet at efficios.com
Fri Oct 5 09:13:37 EDT 2012


I guess this discussion can continue and we can come up with a community

This is a matter of UI naming so it should be decided now before we
release stable since for the complete 2.x cycle we'll have to support this.

Anyone wants to ship in here?


> Hi David
> thanks for the detailed explanation.
> I'm not debating the purpose of the command or that a 2 step approach is
> supported for enabling the consumer. As you described it makes sense to
> have this possibility.
> However I'm debating mainly the name of the command "enable-consumer".
> The command suggests that the consumer will be enabled when executing
> the command. I foresee that a lot of users expect that the consumer is
> enabled after the command execution. I think, a different name would
> improve the user experience.
> Best Regards
> Bernd
> On 10/03/2012 02:27 PM, David Goulet wrote:
>> Hi Bernd,
>> The enable-consumer, by default, always enable a consumer. We added the
>> "extended options" such as the -U/-C/-D/-e to control each part of the
>> API. So let say,
>> $ lttng enable-consumer -k net://localhost
>> This command does two API calls underneath which are
>> lttng_set_consumer_uri and lttng_enable_consumer.
>> However, the set_consumer_uri can be arbitrary long because it has to
>> connect to the relayd (if remote) and set the session. It adds "unknown"
>> latency to the command. So, for someone willing to control the full time
>> window of the streaming setup using the API, it is divided in two calls.
>> This is why we added the extended options so the command line UI could
>> also be controlled on a per API call basis.
>> Is it clear enough?
>> Reply continues below:
>> Bernd Hufmann:
>>> Hello
>>> For the support of LTTng Tools 2.1 in Eclipse, I'm currently trying to
>>> understand how to use the configuration for network streaming with the
>>> updated "lttng create"-command and new "enable-consumer"-command.
>>> a) lttng enable-consumer
>>> I find this command confusing because this command does not always
>>> enables the consumer, even if the command name implieeees so. The
>>> enabling
>>> actually depends on how the command is executed.
>>> Examples:
>>>    * "lttng enable-consumer -k -U net://<remote_addr>" or "lttng
>>>      enable-consumer -k -C tcp://<remote_addr>  -D tcp://<remote_addr>"
>>>      don't enable the consumer. You need to either add option
>>> --enable or
>>>      execute subsequently "lttng enable-consumer --enable"
>>>    * lttng enable-consumer -k net://<remote_addr>  does enable the
>>>      consumer. I took me a while to figure out the difference to the
>>>      example above: The option -U is omitted.
>>> What the command actually provides, is 2 features: A way to configure
>>> streaming (e.g. remote_addr) and a way to enable the consumer. Would it
>>> be better to name it to "lttng configure-consumer"? Also, remove the
>>> support of the possibility to not specify -U, -C or -D. The following
>>> variants of this command should be enough:
>>> lttng configure-consumer -k -U<remote_addr>  [--enable]
>>> lttng configure-consumer -k -C<remote_addr>  -D<remote_addr>  [--enable]
>>> lttng configure-consumer -k --enable
>>> lttng configure-consumer -u -U<remote_addr>  [--enable]
>>> lttng configure-consumer -u -C<remote_addr>  -D<remote_addr>  [--enable]
>>> lttng configure-consumer -u --enable
>>> Please let me know what you think.
>>> b) lttng create [-U<remote_addr>] | [-C<remote_addr>  -D<remote_addr>]
>>> [--no-consumer] [--disable-consumer]
>>>    * Are options --no-consumer or --disable-consumer only applicable for
>>>      streaming?
>> No, also for local consumer.
>>>    * I'm not sure what is the purpose of the options --no-consumer or
>>>      --disable-consumer. Could you please explain the use cases for
>>> using
>>>      --no-consumer or --disable-consumer?
>> This basically disable the consumer for a tracing session. It's not very
>> useful for now but for upcoming snapshots and live tracing, it will make
>> way more sense! :).
>> Again, same idea, the API can control the consumer "state"
>> (enable/disable), so we added these options for the UI.
>> Cheers!
>> David
>>> Thanks
>>> Bernd
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