[lttng-dev] LTTng Tools 2.1 streaming commands

eamcs/eedbhu Bernd.Hufmann at ericsson.com
Fri Oct 5 07:44:24 EDT 2012

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

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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