LTTng » LTTng-tools

I've cooked a patch that fix this issue. So no more socket leaks between the two daemons.

However, I wanted to discuss a behavior of lttng-tools that this bugfix make me realize.

Considering a running tracing session, a kill -9 of the session daemon, the consumer data thread drops dead after a grace period (for now it's 2 seconds). Note that the metadata thread does not do that thus creating two possible scenarios that we should fix or not:

1) Without any modifications, as for now, if the session daemon dies badly, the tracing data is NOT recoverable for the running session since the consumer just stops to consumer data stream because of this grace period once the session daemon dies. Furthermore, the consumer daemon stays alive because the metadata thread does not stop until the stream hang up (Choosing this scenario, we'll have to quick fix this).

2) Removing the grace period makes the consumer stays alive on it's own and continue to extract the data until the application is stopped or dies which trigger a graceful quit of the consumer daemon.

So, what do we want here? Considering a session daemon fatal failure (kill -9), every tracing session is lost (hence the data) or do we want a rogue consumer daemon continuing its work for every stream available? Please note that this brings some issues especially with kernel tracing where if the session daemon goes away, unless unloading the module by hand, there is no possible way to stop the session. Same for the UST tracer, either the application is stopped or the tracing continues at vitam eternam.

For the record. With the new patch in lttng-ust that cleans every stream associated with a lttng-sessiond socket, the consumer timeout grace period will be removed thus giving time to extract the remaining tracing data and finally quit due to the session daemon hang up.

Best of the two worlds.

Patch should be pushed in a jiffy.

Nice David,

I have re-run my test case and your patch proves to work nicely.
All the log collected for the session (prior to the crash of sessionD) were convertable.
Thanks for your help,
Tan