KAFKA-3170; Set default fetch_min_bytes in new consumer to 1

Set default to 1 instead of 1024, this matches the existing doc and feels like a better default value. Have run the unit tests with the change.

Author: Rajini Sivaram <rajinisivaram@googlemail.com>

Reviewers: Jason Gustafson, Ismael Juma, Grant Henke, Guozhang Wang

Closes #832 from rajinisivaram/KAFKA-3170

clients/src/main/java/org/apache/kafka/clients/consumer/ConsumerConfig.java

@@ -226,7 +226,7 @@ public class ConsumerConfig extends AbstractConfig {
                                         CommonClientConfigs.RECEIVE_BUFFER_DOC)
                                 .define(FETCH_MIN_BYTES_CONFIG,
                                         Type.INT,
-                                        1024,
+                                        1,
                                         atLeast(0),
                                         Importance.HIGH,
                                         FETCH_MIN_BYTES_DOC)

docs/upgrade.html

@@ -58,6 +58,7 @@
     <li> The new broker id generation feature can be disable by setting broker.id.generation.enable to false. </li>
     <li> Configuration parameter log.cleaner.enable is now true by default. This means topics with a cleanup.policy=compact will now be compacted by default, and 128 MB of heap will be allocated to the cleaner process via log.cleaner.dedupe.buffer.size. You may want to review log.cleaner.dedupe.buffer.size and the other log.cleaner configuration values based on your usage of compacted topics. </li>
     <li> MirrorMakerMessageHandler no longer exposes <em>handle(record: MessageAndMetadata[Array[Byte], Array[Byte]])</em> method as it was never called. </li>
+    <li> Default value of configuration parameter fetch.min.bytes for the new consumer is now 1 by default. </li>
 </ul>
 
 <h5>Deprecations in 0.9.0.0</h5>