The KafkaConsumer reads randomly from the offset 0

["dali.midou2014@gmail.com" <da...@gmail.com>]

I want to test a Kafka example. I am using Kafka 0.10.0.1.
The producer:
object ProducerApp extends App {
val topic = "topicTest"
val  props = new Properties()
props.put("bootstrap.servers", "localhost:9092")
props.put(ConsumerConfig.GROUP_ID_CONFIG, "consumer")
props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer")
props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer")
val producer = new KafkaProducer[String, String](props)
for(i <- 0 to 20)
{    
val record = new ProducerRecord(topic, "key "+i," value "+i)    
producer.send(record)    
Thread.sleep(100)    
}
}

The consumer (the topic "topicTest" is created with 1 partition):
object ConsumerApp extends App {
val topic = "topicTest"  
val properties = new Properties
properties.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092")
properties.put(ConsumerConfig.GROUP_ID_CONFIG, "consumer")  
properties.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, "false")  
properties.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest")
properties.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer")
properties.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer")
val consumer = new KafkaConsumer[String, String](properties)  
consumer.subscribe(scala.List(topic).asJava)    
while (true) {
consumer.seekToBeginning(consumer.assignment())
val records:ConsumerRecords[String,String] = consumer.poll(20000)
println("records size "+records.count())
records.asScala.foreach(rec => println("offset "+rec.offset()))    
}  
}

The problem is that the consumer reads randomly from the offset 0 at the first iteration but at the other iterations it does. I want to know the reason and how can I make the consumer reads from the offset 0 at all the iterations. The expected result is:
records size 6
offset 0
offset 1
offset 2
offset 3
offset 4
offset 5
records size 6
offset 0
offset 1
offset 2
offset 3
offset 4
offset 5
..
but the obtained result is:
records size 4
offset 2
offset 3
offset 4
offset 5
records size 6
offset 0
offset 1
offset 2
offset 3
offset 4
offset 5
..
 I want that the consumer reads all the records at all the iterations (from the offset 0 to the offset 5)