[erlang-questions] Losing data

Bob Cowdery <>
Thu Jun 2 21:09:40 CEST 2011


Can anyone give me some hints on how to debug this problem. I know its a
long-shot but maybe someone has experience of a similar problem.

I have a real-time system that reads from a device using UDP and writes
back to the same device using UDP. The data processing chain comprises 6
processes:

Reader - Decoder - Input to linked-in-driver - output from
linked-in-driver - Encoder - Writer

With the parameters I'm using I should be writing the same number of
blocks that I am reading. There are sequence numbers on both input and
output blocks. For a while this is what happens, then I start to lose
blocks. I believe in snatches rather than a regular pattern. I can
sometimes hear the disruption in the output and if I stop at that point
I've lost blocks, as many as 40 in one case. However it can run on way
longer than that with no lost blocks.

I've checked every stage of the code with debug statements but
everything seems to pass through correctly.  I've also checked the
message queue length at each stage and it never builds up on any
process. I have no catch-all message handlers. The messages are all
large binary.

The symptoms look like it just can't keep up but If a process was
getting behind I would expect the message q to build up. CPU is 5-7%.

Any ideas would be very welcome.

Bob





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