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I think some data was lost. How can I confirm?

Problem

You believe some data sent over an Aeron UDP channel might have been lost and want to confirm.

Solution

Use the LossStat tool to review if any loss data was captured by Aeron.

Discussion

LossStat logs all the data loss events suffered by Aeron. You must point LossStat at the Media Driver folder specified in the Media Driver Context. For example, if your Media Driver context has the following:

final MediaDriver.Context mediaDriverCtx = new MediaDriver.Context()
    .aeronDirectoryName("/dev/shm/md");

then the path provided to LossStat would be as follows:

java -cp aeron-all-*.jar -Daeron.dir=/dev/shm/md io.aeron.samples.LossStat

An example run:

#OBSERVATION_COUNT,TOTAL_BYTES_LOST,FIRST_OBSERVATION,LAST_OBSERVATION,SESSION_ID,STREAM_ID,CHANNEL,SOURCE
688,4167028,2020-08-16 13:53:39.053+0000,2020-08-16 13:53:41.003+0000,1155221173,8,aeron:udp?endpoint=10.1.1.1:4000;10.1.1.2:60950

This tells us the following about the session 1155221173 on channel aeron:udp?endpoint=10.1.1.1:4000 on stream 8 ⤌⤍ 10.1.1.2:60950 flow:

  • there were 688 data loss events
  • a total of 4,167,028 bytes were impacted
  • the loss first happened at 2020-08-16 16:53:39.053+0000
  • the last loss happened at 2020-08-16 16:53:41.003+0000

If there are no entries, then Aeron believes that no data was lost.

See Also

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