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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