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Bug #1365

open

Repeated snapshots of session in snapshot mode yield sometimes empty results

Added by Stepan Konrad almost 2 years ago. Updated almost 2 years ago.

Status:
New
Priority:
Normal
Assignee:
-
Target version:
-
Start date:
12/15/2022
Due date:
% Done:

0%

Estimated time:

Description

I'm currently evaluating LTTng to use it as a flight-recorder from which I can snapshot traces on demand (potentially multiple times).

What I did to reproduce can also be seen in the reproduce.sh script (I hope, it's self-explanatory) and I also attached the log files (sessiond with -vvv --verbose-consumer, etc.).

Basically, I did:
  • Start a session in snapshot mode (LTTng version 2.13.7 on x86_64)
  • Create 10 ust tracepoints
  • Repeatedly create snapshots
  • Inspect them with babeltrace2 (actually just count the lines)

What I get is that the first couple of snapshots contain the 10 tracepoints and the later snapshots don't. If I vary the number of snaphots, it also varies.
I did not stop the recording on purpose as I think this should still work (according to the documentation).

If you need more/different data/information, I'm happy to provide that.

Thanks a lot in advance!
Stepan

Files

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reproduce.sh (832 Bytes) reproduce.sh Script to reproduce (uses the hello world example from docs) Stepan Konrad, 12/15/2022 09:54 AM
logs.zip (57.2 KB) logs.zip Logs from one reproduce.sh run Stepan Konrad, 12/15/2022 09:54 AM
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 #1

Updated by Mathieu Desnoyers almost 2 years ago

Yes, this is expected due to the current implementation. Please refer to this discussion:

https://lists.lttng.org/pipermail/lttng-dev/2016-December/026799.html

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