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17.3. Change the logging level at runtime

The logging level of the broker can be changed at runtime, without restarting. This is useful to increase the level of logging detail while debugging, then return it to a lower level.
The Qpid Management Framework Broker object has a setLogLevel method to control the logging level. The following C++ code demonstrates calling this method to set the logging level. 
#include <qpid/messaging/Connection.h>
#include <qpid/messaging/Session.h>
#include <qpid/messaging/Sender.h>
#include <qpid/messaging/Receiver.h>
#include <qpid/messaging/Message.h>
#include <qpid/messaging/Address.h>

#include <iostream>

using namespace std;
using namespace qpid::messaging;
using namespace qpid::types;

int main(int argc, char** argv) {
  if (argc < 2) {
    cerr << "Invalid number of parameters, expecting log level (info, trace, warning or so)" << endl;
    return 1;
  }
  string log_level = argv[1];

  Connection connection(argc>2?argv[2]:"localhost:5672");
  connection.open();
  Session session = connection.createSession();
  Sender sender = session.createSender("qmf.default.direct/broker");
  Receiver receiver = session.createReceiver("#reply-queue; {create:always, node:{x-declare:{auto-delete:true}}}");
  Address responseQueue = receiver.getAddress();

  Message message;
  Variant::Map content;
  Variant::Map OID;
  Variant::Map arguments;

  OID["_object_name"] = "org.apache.qpid.broker:broker:amqp-broker";
  arguments["level"] = log_level;

  content["_object_id"] = OID;
  content["_method_name"] = "setLogLevel";
  content["_arguments"] = arguments;

  message.setContentObject(content);
  message.setReplyTo(responseQueue);
  message.setProperty("x-amqp-0-10.app-id", "qmf2");
  message.setProperty("qmf.opcode", "_method_request");
  message.setContentType("amqp/map");

  sender.send(message, true);

  /* receive a response from the broker & check our request was successfully processed */
  Message response;
  if (receiver.fetch(response,qpid::messaging::Duration(30000)) == true) {
    qpid::types::Variant::Map recv_props = response.getProperties();
    if (recv_props["qmf.opcode"] == "_method_response")
      std::cout << "Response: OK" << std::endl;
    else if (recv_props["qmf.opcode"] == "_exception")
      std::cerr << "Error: " << response.getContent() << std::endl;
    else
      std::cerr << "Invalid response received!" << std::endl;
  }
  else
    std::cout << "Timeout: No response received within 30 seconds!" << std::endl;

  receiver.close();
  sender.close();
  session.close();
  connection.close();
  return 0;
      }
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  1. Save the example code to a file set_log_level.cpp.
  2. Modify the Connection URL in the code to resolve to your broker. At the moment it is set to connect to a broker running on port 5672 on the local machine.
  3. Compile the example code: 
    g++ -Wall -lqpidclient -lqpidcommon -lqpidmessaging -lqpidtypes -o set_log_level set_log_level.cpp
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  4. Use the complied program to change the log level of the broker: 
    ./set_log_level "trace+"
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  5. To observe the change in the logging level, tail the server log as you run the program.
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