no match of right hand side value: []

[Schultzer]

Hi @koudelka, we are using HoneyDew in production, for our data ingestion. We are using the global Mnesia queue in a multi node setup running nightly jobs and we have notice this MatchError error appearing from time to time:

no match of right hand side value: []

lib/honeydew/queue/mnesia.ex:145 anonymous fn/2 in Honeydew.Queue.Mnesia.ack/2
mnesia_tm.erl:746 :mnesia_tm.non_transaction/5
lib/honeydew/queue/mnesia.ex:144 Honeydew.Queue.Mnesia.ack/2
lib/honeydew/queue.ex:235 Honeydew.Queue.do_ack/2
lib/honeydew/queue.ex:267 Honeydew.Queue.handle_cast/2
gen_server.erl:680 :gen_server.try_dispatch/4
gen_server.erl:756 :gen_server.handle_msg/6
proc_lib.erl:226 :proc_lib.init_p_do_apply/3

GenServer #PID<0.7182.0> terminating ** (stop) an exception was raised: ** (MatchError) no match of right hand side value: [] (honeydew 1.4.6) lib/honeydew/queue/mnesia.ex:145: anonymous fn/2 in Honeydew.Queue.Mnesia.ack/2 (mnesia 4.18) mnesia_tm.erl:746: :mnesia_tm.non_transaction/5 (honeydew 1.4.6) lib/honeydew/queue/mnesia.ex:144: Honeydew.Queue.Mnesia.ack/2 (honeydew 1.4.6) lib/honeydew/queue.ex:235: Honeydew.Queue.do_ack/2 (honeydew 1.4.6) lib/honeydew/queue.ex:267: Honeydew.Queue.handle_cast/2 (stdlib 3.13.2) gen_server.erl:680: :gen_server.try_dispatch/4 (stdlib 3.13.2) gen_server.erl:756: :gen_server.handle_msg/6 (stdlib 3.13.2) proc_lib.erl:226: :proc_lib.init_p_do_apply/3 (mnesia 4.18) mnesia_tm.erl:752: :mnesia_tm.non_transaction/5 (honeydew 1.4.6) lib/honeydew/queue/mnesia.ex:144: Honeydew.Queue.Mnesia.ack/2 (honeydew 1.4.6) lib/honeydew/queue.ex:235: Honeydew.Queue.do_ack/2 (honeydew 1.4.6) lib/honeydew/queue.ex:267: Honeydew.Queue.handle_cast/2 (stdlib 3.13.2) gen_server.erl:680: :gen_server.try_dispatch/4 (stdlib 3.13.2) gen_server.erl:756: :gen_server.handle_msg/6 (stdlib 3.13.2) proc_lib.erl:226: :proc_lib.init_p_do_apply/3 Last message: {:"$gen_cast", {:ack, %Honeydew.Job{by: :"redacted", completed_at: nil, delay_secs: 0, enqueued_at: 1615879481049, failure_private: nil, from: nil, job_monitor: #PID<65709.14594.2>, private: -576460752303404767, queue: {:global, :job_queue}, result: nil, started_at: 1615964552907, task: {:sync, []}}}}

[koudelka]

Hey there @Schultzer! This seems to happen when a job is "acked" (removed from the queue). The specific line indicates that the job has already been removed from the queue when the ack comes in, which is rather curious. I don't believe that the error is indicative of a violation of the "at least once" guarantee, but it could also mean that the job is being run more than once somehow. By chance, do any of your logs indicate that this might be so?

[Schultzer]

By chance, do any of your logs indicate that this might be so?

Non currently, but I'll investigate.