consumer poll returns no records unless called more than once, why?

[Padgett, Ben]

        //this code

        Properties consumerProps = new Properties();
        consumerProps.put("bootstrap.servers", "localhost:9092");


        //without deserializer it fails, which makes sense. the documentation 
however doesn't show this
        consumerProps.put("key.deserializer", 
"org.apache.kafka.common.serialization.StringDeserializer");
        consumerProps.put("value.deserializer", 
"org.apache.kafka.common.serialization.StringDeserializer");


        //why is serializer required? without this it fails to return results 
when calling poll
        consumerProps.put("key.serializer", 
"org.apache.kafka.common.serializers.StringSerializer");
        consumerProps.put("value.serializer", 
"org.apache.kafka.common.serializers.StringSerializer");


        consumerProps.put("group.id", "test");
        consumerProps.put("enable.auto.commit", "true");
        consumerProps.put("auto.commit.interval.ms", "1000");
        consumerProps.put("session.timeout.ms", "30000");

        org.apache.kafka.clients.consumer.KafkaConsumer<String, String> 
consumer = new org.apache.kafka.clients.consumer.KafkaConsumer<String, 
String>(consumerProps);

        TopicPartition topicPartition = new TopicPartition("project-created", 
0);
        consumer.subscribe(topicPartition);

        consumer.seeekToBeginning(topicPartition);

        //each scenerio code goes here



        I have a scenerio where it returns records and a scenerio where no 
records are returned. Could anyone provide insight on why this happens?



        //without a loop consumer.poll(100) returns no records
        //after poll is called a second time it returns records
        boolean run = true;
        while (run) {
            ConsumerRecords<String, String> records = consumer.poll(100);
        }



        //why would this return zero records?
        ConsumerRecords<String, String> records = consumer.poll(100);


//This is to show that there are records for topic "project-created"

bin/kafka-console-consumer.sh --zookeeper localhost:2181 --topic 
project-created --from-beginning
3a543cf4-13e4-42b6-8c72-54b733228c75
c298d41e-4ae5-4f4f-933e-f745969aaf98
2036ef69-9694-4ee8-a40c-50cddf982edb
08d90698-8c75-4c4b-8ce6-b0b12d3de0d6
249d0e8c-cd38-41b0-ae7f-bdfa7fa8f76e
84d87e45-cd10-4797-bfe3-d540e26e56cc
a8c74f78-cb7a-4c74-873b-a0e587af646c
42eeff6e-22fd-40c4-96b4-91a3df356ec7
bef622b6-3ac1-489b-9837-ab9c2b0399d1
03e9d567-fadf-46dc-8097-4bc327a0942e
df5d93d6-30de-494a-8d82-45cd8b4fc785
eb5a194f-083d-4a0f-bbb7-155056acd929
192dfbb7-4f4f-4550-a1b4-ab9bc83be825
b7845e7e-b477-476d-b115-b0a9d076c52e
f8ea2d0f-bc76-44a8-86ef-2b3e0adf7755
8ee28e0c-5a8e-47c8-a939-f5dc6d7be3f9
fbe30ae3-c383-4e27-8f70-f3c63ed82fed
50fa9166-cc0d-4d12-8d86-c922062519cd
50ceb437-2556-4a9a-8a13-93bfc130e914
f1f5ad0b-7739-47fd-be57-ac093f728004
0df1a923-92d9-416a-861a-d65590f7e4c2
849e5e2b-3803-4a6e-86fc-64fe80d81268
163d9c1c-6224-4dad-a23a-1c90c9791e1f