exception exit: timeout in gen_server:call

[ostinelli]

All,
We are experiencing the following error when calling a transaction as per the README:

equery(PoolName, Stmt, Params) ->
    poolboy:transaction(PoolName, fun(Worker) ->
        gen_server:call(Worker, {equery, Stmt, Params})
    end).

** exception exit: {timeout,{gen_server,call,
                                        [keys_db,{checkout,#Ref<0.0.1.156295>,true},5000]}}
     in function  gen_server:call/3 (gen_server.erl, line 212)
     in call from poolboy:checkout/3 (/home/ubuntu/workspace/myapp/_build/default/lib/poolboy/src/poolboy.erl, line 55)
     in call from poolboy:transaction/3 (/home/ubuntu/workspace/myapp/_build/default/lib/poolboy/src/poolboy.erl, line 74)

The process queue keeps on increasing, and I can see the following:

3> erlang:process_info(whereis(keys_db)).  
[{registered_name,keys_db},
 {current_function,{gen,do_call,4}},
 {initial_call,{proc_lib,init_p,5}},
 {status,waiting},
 {message_queue_len,11906},
 {messages,[{'$gen_cast',{cancel_waiting,#Ref<0.0.1.138090>}},
            {'$gen_call',{<0.15224.0>,#Ref<0.0.1.139621>},
                         {checkout,#Ref<0.0.1.139620>,true}},
            {'$gen_call',{<0.15139.0>,#Ref<0.0.1.139649>},
                         {checkout,#Ref<0.0.1.139648>,true}},
            {'$gen_cast',{cancel_waiting,#Ref<0.0.1.138159>}},
            {'$gen_cast',{cancel_waiting,#Ref<0.0.1.138175>}},
            {'$gen_cast',{cancel_waiting,#Ref<0.0.1.138232>}},
            {'$gen_cast',{cancel_waiting,#Ref<0.0.1.138252>}},
            {'$gen_cast',{cancel_waiting,#Ref<0.0.1.138261>}},
            {'$gen_cast',{cancel_waiting,#Ref<0.0.1.138286>}},
            {'$gen_call',{<0.15235.0>,#Ref<0.0.1.139774>},
                         {checkout,#Ref<0.0.1.139773>,true}},
            {'$gen_cast',{cancel_waiting,#Ref<0.0.2.77777>}},
            {'$gen_cast',{cancel_waiting,#Ref<0.0.1.138318>}},
            {'$gen_cast',{cancel_waiting,#Ref<0.0.1.138336>}},
            {'$gen_call',{<0.15233.0>,#Ref<0.0.1.139816>},
                         {checkout,#Ref<0.0.1.139815>,true}},
            {'$gen_call',{<0.15245.0>,#Ref<0.0.1.139854>},
                         {checkout,#Ref<0.0.1.139853>,true}},
            {'$gen_call',{<0.15237.0>,#Ref<0.0.2.78173>},
                         {checkout,#Ref<0.0.2.78172>,...}},
            {'$gen_cast',{cancel_waiting,#Ref<0.0.1.138407>}},
            {'$gen_call',{<0.15228.0>,...},{...}},
            {'$gen_call',{...},...},
            {'$gen_call',...},
            {...}|...]},
 {links,[<0.714.1>,<0.817.1>,<0.947.1>,<0.1015.1>,<0.1045.1>,
         <0.1048.1>,<0.1038.1>,<0.983.1>,<0.1002.1>,<0.962.1>,
         <0.877.1>,<0.909.1>,<0.938.1>,<0.892.1>,<0.849.1>,<0.866.1>,
         <0.832.1>,<0.765.1>,<0.789.1>,<0.804.1>|...]},
 {dictionary,[{'$initial_call',{poolboy,init,1}},
              {'$ancestors',[pgpool_sup,<0.673.0>]}]},
 {trap_exit,true},
 {error_handler,error_handler},
 {priority,normal},
 {group_leader,<0.672.0>},
 {total_heap_size,393326},
 {heap_size,196650},
 {stack_size,33},
 {reductions,14837255},
 {garbage_collection,[{max_heap_size,#{error_logger => true,
                                       kill => true,
                                       size => 0}},
                      {min_bin_vheap_size,46422},
                      {min_heap_size,233},
                      {fullsweep_after,10},
                      {minor_gcs,3}]},
 {suspending,[]}]

Do you have an insight of what may be going wrong? I see that the process status is waiting...

Thank you,
r.

[ostinelli]

Seems like an issue in flow control. What is the best way to know if there's an available worker, before calling a transaction?