----- Message original ----- > De: "lttng-dev" <lttng-dev@lists.lttng.org> > À: "lttng-dev" <lttng-dev@lists.lttng.org> > Envoyé: Mardi 21 Décembre 2021 01:47:12 > Objet: [lttng-dev] Running trace-rotate and session-rotate together
> Hi, > 1. In the lttng-enable-rotation manpage it is mentioned that we should not use > trace rotate when automatic session rotate is enabled. Can you please tell me > why? > ``` > Important > You may only use the enable-rotation command when: > * The selected recording session was created in normal mode or in network > streaming mode > (see lttng-create(1)). > * No channel was created with a configured trace file count or size limit (see > the > --tracefile-size and --tracefile-count options of the lttng-enable-channel(1) > command). > ``` Hi, The reason mostly boils down to the fact that we didn't see a use case for this. Hence, it's not implemented nor tested. Let me know if you have a use case for combining both features, though. > 2. When automatic session rotate is running, is there any race condition in > writing the current ring buffers and archiving the current trace chunk? I am not sure I understand your question, but I think you're asking if session rotations are "atomic" with respect to the switchover of all per-CPU streams from one trace archive to the next? The switchover is not instantaneous. The file output of each per-CPU stream is switched to the new trace archive sequentially. That leaves you with a window of time during which information, for a given stream, may be found in either the old trace archive or the new one. To be clear, no information is ever duplicated or lost during this operation. I briefly touched on this topic in a presentation at the Open Source Summit 2018, see slide 32+[1] The various colours represent successive trace archives produced by session rotations. This transition window makes writing analyses a bit harder since the beginning and end of trace archives may not have all of the information for all per-CPU streams during a short window of time. That window is contained between issuing the rotation and receiving a confirmation that it has been completed (using the CLI or the liblttng-ctl API). You can see that in that context, I chose to process trace archives in pairs to constitute an "effective trace archive" (slide 34) during which I can be sure I always have access to all events from all per-CPU streams. Thanks, Jérémie [1] https://events19.linuxfoundation.org/wp-content/uploads/2017/12/Fine-grained-Distributed-Application-Monitoring-Using-LTTng-J%C3%A9r%C3%A9mie-Galarneau-EfficiOS.pdf > -------------------------------------------------------------- > Regards, > Subrata Paul > _______________________________________________ > lttng-dev mailing list > lttng-dev@lists.lttng.org > https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
