Unstable erlang compared to java or perl

Petter Egesund <>
Sun Nov 7 15:49:57 CET 2010


Hi, I have a small program with lots of memory-updates which I try to
run in Erlang.

The same algorithm works fine in both Java and Perl, but fails in
Erlang because the program runs out of memory - and I can not figure
out why. Frustrating, as my Erlang-versjon seems to be the easiest to
scale as well as being the most readable.

The program is threaded and each thread writes to a ets-table which is
created at the beginning of the thread. When the thread dies I try to
do a ets:delete(Table), like described in the manual, but the memory
used by the thread never seems to be released.

Some facts:

- The memory usage of each thread is rather constant. This is
confirmed when I use ets:i() to show info about memory usage.
- The number of threads are constant - confirmed by both running top
and writing out the number of threads regularly. When a thread dies, I
create a new one.
- I have tried to end the thread by sending a exit-signal as the last
statement. This helps some, but does not solve the leak.
- I put small lists of size 3-4 integers into the ets as values, the
keys are list of same size as well.
- I garbage-collect each thread before it dies, as well as doing
regular global garbage-collects. No help.
- Information from ets:i() about memory when I sum usage by each
thread, is much lower than stated by memory() when i run
erlang:memory(). This might indicate something? Does not seem logical
to me, at least.
- Info from erlang:memory is about half of what top/the os tells.
- I am running on ubuntu, 64-bit, 14A but I have tried 14B as well.

Any clues? Dump from ets:i() and erlang:memory() is like below.

Cheers,

Petter

--- dump ---

eNumber of processes: 27
ets:i():
 id              name              type  size   mem      owner
 ----------------------------------------------------------------------------
 13              code              set   261    10692    code_server
 4110            code_names        set   58     7804     code_server
 6746271765      the_synapses      ordered_set 5425194 113336012 <0.47.0>
 7022018584      the_synapses      ordered_set 15143493 310909950 <0.48.0>
 7774416922      the_synapses      ordered_set 8794649 182005810 <0.49.0>
 ac_tab          ac_tab            set   6      848      application_controller
 file_io_servers file_io_servers   set   0      302      file_server_2
 global_locks    global_locks      set   0      302      global_name_server
 global_names    global_names      set   0      302      global_name_server
 global_names_ext global_names_ext  set   0      302      global_name_server
 global_pid_ids  global_pid_ids    bag   0      302      global_name_server
 global_pid_names global_pid_names  bag   0      302      global_name_server
 inet_cache      inet_cache        bag   0      302      inet_db
 inet_db         inet_db           set   29     571      inet_db
 inet_hosts_byaddr inet_hosts_byaddr bag   0      302      inet_db
 inet_hosts_byname inet_hosts_byname bag   0      302      inet_db
 inet_hosts_file_byaddr inet_hosts_file_byaddr bag   0      302      inet_db
 inet_hosts_file_byname inet_hosts_file_byname bag   0      302      inet_db
 neurone_counter neurone_counter   set   258394 1846182  entity_server
 neurone_group_counter neurone_group_counter set   6      344
entity_group_server
 neurone_group_name neurone_group_name set   6      426      entity_group_server
 neurone_group_name_reverse neurone_group_name_reverse set   6
426      entity_group_server
 neurone_name    neurone_name      set   258394 11824602 entity_server
 neurone_name_reverse neurone_name_reverse set   258394 11824602 entity_server
memory(): 	  [{total,5568669792},
                   {processes,1138936},
                   {processes_used,1128120},
                   {system,5567530856},
                   {atom,349769},
                   {atom_used,336605},
                   {binary,82704},
                   {code,3046365},
                   {ets,5562163256}]


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