[lttng-dev] lttng-health-check

[Jérémie Galarneau]

On Thu, Mar 20, 2014 at 2:27 PM, Thibault, Daniel
<Daniel.Thibault at drdc-rddc.gc.ca> wrote:
> LTTNG_HEALTH_APP_MANAGE:
> The lttng-health-check function will report the health of the application command socket manager subsystem.  This session daemon thread (thread_manage_apps) watches the application command sockets; their closure indicates application shutdown (more accurately, shutdown of the application's tracepoint provider) and triggers unregistration.
>
> Would it be correct to say that if this component malfunctions, closure of application trace files (if tracing in per-process ID mode) will be delayed until the session is destroyed, but that there won't be any other truly deleterious consequences?  It seems unlikely any events will be lost (the consumer will commit the buffer contents normally), and this thread failure would not hamper tracing of other applications nor client-controlled enabling and disabling of events.  The lttng list of event sources would include ghosts (dead-and-gone apps).  Could lttng hang if the client tried to toggle the enabling of events published by the ghosts?
>

It depends on where the "manage apps" thread hangs/dies. Both
scenarios are a possibility. The outcome depends largely on whether or
not the thread was holding a lock at that time.

> I guess my point is that, of all the possible health failures, this seems the least catastrophic one.
>

One important thing to understand is that the health check is not an
error recovery mechanism; it is only meant as a tool to detect
unexpected internal errors from which we can only recover by
restarting.

Regards,
Jérémie

> Daniel U. Thibault
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-- 
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com