[erlang-questions] High lock contention on dist_tables

Brian Picciano mediocregopher@REDACTED
Fri Apr 19 21:24:12 CEST 2013

We have a pool of 3 erlang nodes, all on different servers. Every
afternoon, without fail, we start seeing lots of messages between the nodes
start having really high latency, on the order of tens of seconds. Today we
ran lcnt on them to see if there's anything there, and found that on one of
the nodes dist_tables had a significantly higher lock percentage then
anything else, and definitely higher then on the other boxes:

(node@REDACTED)8> lcnt:conflicts().

                 lock     id   #tries  #collisions  collisions [%]  time
[us]  duration [%]
                -----    ---  ------- ------------ ---------------
---------- -------------
           dist_table      1  3468191      1242055         35.8128
 153712413      255.2521
            run_queue     24 76969638      4088578          5.3119
14468656       24.0264
        process_table      1  2015686       147148          7.3001
 3208529        5.3280
          timer_wheel      1 12214948       834737          6.8337
 3076638        5.1090
            timeofday      1 18231600       594487          3.2608
 1491633        2.4770

while on the other boxes it had closer to 3. On the box with the high lock
contention we also saw much higher load then on the other boxes.

My question is: what is this lock? We couldn't find much online except that
it appears to have to do with communication between nodes, but we're not
sure what. Also, what, if anything, could we do to mitigate this problem?

(We're running erlang 16B)
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