Any advice on how to debug lost events? Thanks in advance!
On Wed, Oct 31, 2018 at 2:58 PM Alok Priyadarshi <alo...@gmail.com> wrote: > We are tracing a multi-process application that generates high-frequency > user-space trace events. > > Environment: > - Ubuntu 16.04 LTS > - Lttng 2.10.4 - KeKriek > > Session: > - Snapshot mode > - One channel with default config: > overwrite=1, subbuf_size=524288, num_subbuf=4 > > We have noticed that a few events are missing. I understand that in > overwrite mode we can lose entire sub-buffers but IIUC we would only lose > events at the beginning, not in-between events in a sub-buffer. > > Is it not true that only the oldest sub-buffer is overwritten and when > overwrite happens, none of the latest events are discarded? > > Few more things to note: > - Before lttng-snapshot-record, we stop tracing as recommended by the > documentation > - Packet context field events_discarded is always set to 0 > - Event loss seems to happen around packet transition. I have noticed this > in at least two traces > > The snapshot mode seems perfect for our use case. It is OK to lose events > from either ends of the snapshot, but it is essential to not lose any > in-between events. I was under the impression that overwrite mode > guarantees that. If not, is there anything else we can try? >
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