my socket can't handle the load

Pablo Platt <>
Wed Jun 2 17:27:40 CEST 2010


Hi,

I'm writing a driver to a database that is using a tcp socket.
There are two types of messages, "send and forget" and "send and receive".
I have a gen_server that is responsible for opening the socket, receive a message from a process and sending it to the socket and receive responses and pass them to the caller.
The gen_server saves a list of {request_id, CallerPid} in the state to know who to respond to when a packet is received from the db. 

Everything works when the rate of messages is low but when increasing it I'm starting to get gen_server timeout error on the requestor.
Do I need to add/change parameters when opening the socket?
Should I queue requests and wait for a response before sending the next request or is it ok to send several requests one after the other?

Thanks

The client sends a request using either:
Resp = gen_server:call(Conn, {request, Request})
or
gen_server:cast(Conn, {request, Request})


The relevant gen_server code:

init([Host, Port]) ->
    Socket = open_socket(Host, Port),
    {ok, #state{socket=Socket, req_id=1}}.

open_socket(Host, Port) ->
    case gen_tcp:connect(Host, Port, [binary, {active, true}]) of
        {ok, Sock} ->
            Sock;
        {error, Reason} ->
            exit({open_socket_failed, Reason})
    end.

handle_call({request, Packet}, From, State) ->
    ReqID = State#state.req_id + 1,
    gen_tcp:send(State#state.socket, Packet),
    {noreply, State#state{req_id=ReqID, requests=[{ReqID, From}|State#state.requests]}};

handle_cast({request, Packet}, State) ->
    ReqID = State#state.req_id + 1,
    gen_tcp:send(State#state.socket, Packet),
    {noreply, State#state{req_id=ReqID}}.

handle_info({tcp, _Socket, Data}, State) ->
    RawResp = <<(State#state.resp)/binary, Data/binary>>,
    case check_packet:decode_response(RawResp) of
        undefined ->
            {noreply, State#state{resp = RawResp}};
        {Resp, Tail} ->
            ResponseTo = get_requestor(Resp),
            {value, {ResponseTo, Client}, NewRequests} = lists:keytake(ResponseTo, 1, State#state.requests),
            gen_server:reply(Client, Resp),
            {noreply, State#state{resp = Tail, requests=NewRequests}}
    end;

% the following never been called, even when I'm getting the error.
handle_info({tcp_closed, _Socket}, State) ->   
    {noreply, State};

handle_info({tcp_error, _Socket, _Reason}, State) ->
    {noreply, State}.

terminate(_Reason, _State) ->
    ok.



      


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