[lttng-dev] Configurable tracepath?

Jesper Derehag jderehag at hotmail.com
Wed Mar 25 11:52:48 EDT 2015


We have run into an issue with unique per-session tracepaths. 

In my particular setup I am using relayd to centralize alot of consumers (not really important to this discussion, but thought I'd mention it anyway).
So the problem is that I have very limited quota for %outputpath. So to manage the quota fairly between channels I am using --tracefile-size to limit the size of each channel and thus preventing them from starving eachother out.
BUT, say I would want to restart the session for some reason, in my case it might be that the card running a specific session reboots, and then relayd would get a new session & channel, and thus create a new folder for that data. But since the old data still remains, I would run into the quota limit.. 

Below is how the tracepaths are created in pseudo-code:

per-pid tracing:
   tracepath = %outputpath/%pid/%session_name-%pid-%datetime

per-uid tracing:
   tracepath = %outputpath/uid/%uid/%arch-bit

So just reading this little snippet I am guessing one could avoid this particular problem by doing per-uid tracing, but that seems like an unnecessary workaround for what would seem like a trivial problem?

Would it instead be feasable to have the channel->path_name configurable, so that you essentially could avoid the uniqueness of the path (pid & datetime)?

Or is that instead opening pandoras box w.r.t. to tracefile consistency and contention?


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