KAFKA-808 Migration tool internal queue between consumer and producer…

… threads should be configurable; reviewed by Jun Rao

core/src/main/scala/kafka/tools/KafkaMigrationTool.java

@@ -134,6 +134,13 @@ public static void main(String[] args) throws InterruptedException, IOException
       .describedAs("Java regex (String)")
       .ofType(String.class);
 
+    ArgumentAcceptingOptionSpec<Integer> queueSizeOpt
+      =  parser.accepts("queue.size", "Number of messages that are buffered between the 0.7 consumer and 0.8 producer")
+      .withRequiredArg()
+      .describedAs("Queue size in terms of number of messages")
+      .ofType(Integer.class)
+      .defaultsTo(10000);
+
     OptionSpecBuilder helpOpt
       = parser.accepts("help", "Print this message.");
 
@@ -212,7 +219,8 @@ public static void main(String[] args) throws InterruptedException, IOException
       kafkaProducerProperties_08.load(new FileInputStream(producerConfigFile_08));
       kafkaProducerProperties_08.setProperty("serializer.class", "kafka.serializer.DefaultEncoder");
       // create a producer channel instead
-      ProducerDataChannel<KeyedMessage<String, byte[]>> producerDataChannel = new ProducerDataChannel<KeyedMessage<String, byte[]>>(numProducers);
+      int queueSize = options.valueOf(queueSizeOpt);
+      ProducerDataChannel<KeyedMessage<String, byte[]>> producerDataChannel = new ProducerDataChannel<KeyedMessage<String, byte[]>>(queueSize);
       int threadId = 0;
 
       Runtime.getRuntime().addShutdownHook(new Thread() {