KAFKA-3525; getSequenceId should return 1 for first data node creation

ZkUtils.getSequenceId() method is used to generate broker id sequence numbers. During startup, each broker updates the data at /brokers/seqid zk path and returns stat.getVersion as next sequence id.

stat.getVersion returns "1" for first data update. So ZkUtils.getSequenceId() should return "1" on first data update.

Author: Manikumar reddy O <manikumar.reddy@gmail.com>

Reviewers: Flavio Junqueira <fpj@apache.org>, Ismael Juma <ismael@juma.me.uk>

Closes #1224 from omkreddy/KAFKA-3525

core/src/main/scala/kafka/server/KafkaConfig.scala

@@ -356,7 +356,7 @@ object KafkaConfig {
   val ZkSyncTimeMsDoc = "How far a ZK follower can be behind a ZK leader"
   val ZkEnableSecureAclsDoc = "Set client to use secure ACLs"
   /** ********* General Configuration ***********/
-  val BrokerIdGenerationEnableDoc = s"Enable automatic broker id generation on the server? When enabled the value configured for $MaxReservedBrokerIdProp should be reviewed."
+  val BrokerIdGenerationEnableDoc = s"Enable automatic broker id generation on the server. When enabled the value configured for $MaxReservedBrokerIdProp should be reviewed."
   val MaxReservedBrokerIdDoc = "Max number that can be used for a broker.id"
   val BrokerIdDoc = "The broker id for this server. If unset, a unique broker id will be generated." +
   "To avoid conflicts between zookeeper generated broker id's and user configured broker id's, generated broker ids" +

core/src/main/scala/kafka/utils/ZkUtils.scala

@@ -792,24 +792,16 @@ class ZkUtils(val zkClient: ZkClient,
   /**
     * This API produces a sequence number by creating / updating given path in zookeeper
     * It uses the stat returned by the zookeeper and return the version. Every time
-    * client updates the path stat.version gets incremented
+    * client updates the path stat.version gets incremented. Starting value of sequence number is 1.
     */
   def getSequenceId(path: String, acls: java.util.List[ACL] = DefaultAcls): Int = {
+    def writeToZk: Int = zkClient.writeDataReturnStat(path, "", -1).getVersion
     try {
-      val stat = zkClient.writeDataReturnStat(path, "", -1)
-      stat.getVersion
+      writeToZk
     } catch {
-      case e: ZkNoNodeException => {
-        createParentPath(BrokerSequenceIdPath, acls)
-        try {
-          zkClient.createPersistent(BrokerSequenceIdPath, "", acls)
-          0
-        } catch {
-          case e: ZkNodeExistsException =>
-            val stat = zkClient.writeDataReturnStat(BrokerSequenceIdPath, "", -1)
-            stat.getVersion
-        }
-      }
+      case e1: ZkNoNodeException =>
+        makeSurePersistentPathExists(path)
+        writeToZk
     }
   }
 

core/src/test/scala/unit/kafka/server/ServerGenerateBrokerIdTest.scala

@@ -187,4 +187,12 @@ class ServerGenerateBrokerIdTest extends ZooKeeperTestHarness {
     }
     true
   }
+
+  @Test
+  def testGetSequenceIdMethod() {
+    val path = "/test/seqid"
+    (1 to 10).foreach { seqid =>
+      assertEquals(seqid, zkUtils.getSequenceId(path))
+    }
+  }
 }