For me it seems like kafka transactional producer is behaving like a regular producer, the meesages are visible on the topic as send is called for each message. Maybe I am missing something basic. I was expecting the messages to appear in the topic only after the producer commit method is called. In my code below produce.commitTransactions() is commented out but I still get the messages in the topic. Thanks for any pointers.
public static void main(String[] args) {
try {
Properties producerConfig = new Properties();
producerConfig.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "...");
producerConfig.put(ProducerConfig.CLIENT_ID_CONFIG, "transactional-producer-1");
producerConfig.put(ProducerConfig.ENABLE_IDEMPOTENCE_CONFIG, true); // enable idempotence
producerConfig.put(ProducerConfig.TRANSACTIONAL_ID_CONFIG, "test-transactional-id-1"); // set transaction id
producerConfig.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringSerializer");
producerConfig.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringSerializer");
Producer<String, String> producer = new KafkaProducer<>(producerConfig);
producer.initTransactions(); //initiate transactions
try {
producer.beginTransaction(); //begin transactions
for (Integer i = 0; i < 1000; i++) {
producer.send(new ProducerRecord<String, String>("t_test", i.toString(), "value_" + i));
}
// producer.commitTransaction(); //commit
} catch (KafkaException e) {
// For all other exceptions, just abort the transaction and try again.
producer.abortTransaction();
}
producer.close();
} catch (Exception e) {
System.out.println(e.toString());
}
}
When it comes to transactions in Kafka you need to consider a Producer/Consumer pair. A Producer itself, as you have observed, is just producing data and either committing the transaction or not.
Only in interplay with a consumer you can "complete" a transaction by setting the KafkaConsumer configuration isolation.level set to read_committed (by default it is set to read_uncommitted). This configuration is described as:
isolation.level: Controls how to read messages written transactionally. If set to read_committed, consumer.poll() will only return transactional messages which have been committed. If set to read_uncommitted' (the default), consumer.poll() will return all messages, even transactional messages which have been aborted. Non-transactional messages will be returned unconditionally in either mode.
Related
I am using Kafka Transactional producer to post atomically to 2 topics on a broker. My code looks similar to this:
Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("transactional.id", "my-transactional-id");
Producer<String, String> producer = new KafkaProducer<>(props, new StringSerializer(), new StringSerializer());
producer.initTransactions();
try {
producer.beginTransaction();
for (int i = 0; i < 100; i++)
producer.send(new ProducerRecord<>("my-topic", Integer.toString(i), Integer.toString(i)));
producer.commitTransaction();
} catch (ProducerFencedException | OutOfOrderSequenceException | AuthorizationException e) {
// We can't recover from these exceptions, so our only option is to close the producer and exit.
producer.close();
} catch (KafkaException e) {
// For all other exceptions, just abort the transaction and try again.
producer.abortTransaction();
}
producer.close();
Acc. to kafka docs and my understanding, initTransactions() has to be called only once per producer session, and it registers that producer instance to the broker with the specified transactional-id.
Now, in my case I need to deploy this code to several servers using same kafka broker.
Do I need different transactional Ids for each instance?
Is there any way to close initTransactions() once it is called so that it doesn't block other producers executing transactions as they have same transactional-id.
P.s. I don't want to close the producer and re-instantiate it after every sent transaction as this can impact performance, I believe. How can we implement an efficient solution to this problem?
I'm new to kafka, I have the following sample code :
KafkaConsumer<String,String> kc = new KafkaConsumer<String, String>(props);
while(true) {
List<String> topicNames = Arrays.asList(topics.split(","));
if (!kc.assignment().isEmpty()) {
kc.unsubscribe();
}
kc.subscribe(topicNames);
ConsumerRecords<String, String> recv = kc.poll(1000L);
if (!recv.isEmpty()) {
System.out.println("NOT EMPTY");
}
}
The recv is always empty but if I try to increment the pool timeout the records are returned, also if I cut off the unsubscribe part.
I've taken this piece of code from an integration proprietary software and I cannot modify it.
So my question is: Is this only a timing problem or there is more?
There is a lot that happens when a consumer (re)subscribes to a topic.
Very roughly and as far as I remember the consumer will:
request cluster information
request consumer group metadata
make a JOIN_GROUP request
be assigned certain partitions
The underlying mechanisms are even more complicated if there are more consumers within the same group. That's because the partitions should be reassigned between all the consumers within the group.
That is why:
1000 millis might not be enough for all this and you didn't poll anything in time
you polled something when you increased the timeout because Kafka managed to perform all of these bootstrapping operations
you polled something when you removed the unsubscription to the topics because most likely your consumer was already subscribed
So there is a timing issue. And I think that there is something more - un/subscribing to a topic within an infinite loop makes no sense to me (see the other answer).
You should subscribe to your topics only once at the beginning. Like this:
final KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props);
consumer.subscribe(Arrays.asList("foo", "bar"));
while (true) {
final ConsumerRecords<String, String> records = consumer.poll(100);
for (ConsumerRecord<String, String> record : records)
System.out.printf("offset = %d, key = %s, value = %s%n", record.offset(), record.key(), record.value());
}
I have Kafka commit policy set to latest and missing first few messages. If I give a sleep of 20 seconds before starting to send the messages to the input topic, everything is working as desired. I am not sure if the problem is with consumer taking long time for partition rebalancing. Is there a way to know if the consumer is ready before starting to poll ?
You can use consumer.assignment(), it will return set of partitions and verify whether all of the partitions are assigned which are available for that topic.
If you are using spring-kafka project, you can include spring-kafka-test dependancy and use below method to wait for topic assignment , but you need to have container.
ContainerTestUtils.waitForAssignment(Object container, int partitions);
You can do the following:
I have a test that reads data from kafka topic.
So you can't use KafkaConsumer in multithread environment, but you can pass parameter "AtomicReference assignment", update it in consumer-thread, and read it in another thread.
For example, snipped of working code in project for testing:
private void readAvro(String readFromKafka,
AtomicBoolean needStop,
List<Event> events,
String bootstrapServers,
int readTimeout) {
// print the topic name
AtomicReference<Set<TopicPartition>> assignment = new AtomicReference<>();
new Thread(() -> readAvro(bootstrapServers, readFromKafka, needStop, events, readTimeout, assignment)).start();
long startTime = System.currentTimeMillis();
long maxWaitingTime = 30_000;
for (long time = System.currentTimeMillis(); System.currentTimeMillis() - time < maxWaitingTime;) {
Set<TopicPartition> assignments = Optional.ofNullable(assignment.get()).orElse(new HashSet<>());
System.out.println("[!kafka-consumer!] Assignments [" + assignments.size() + "]: "
+ assignments.stream().map(v -> String.valueOf(v.partition())).collect(Collectors.joining(",")));
if (assignments.size() > 0) {
break;
}
try {
Thread.sleep(1_000);
} catch (InterruptedException e) {
e.printStackTrace();
needStop.set(true);
break;
}
}
System.out.println("Subscribed! Wait summary: " + (System.currentTimeMillis() - startTime));
}
private void readAvro(String bootstrapServers,
String readFromKafka,
AtomicBoolean needStop,
List<Event> events,
int readTimeout,
AtomicReference<Set<TopicPartition>> assignment) {
KafkaConsumer<String, byte[]> consumer = (KafkaConsumer<String, byte[]>) queueKafkaConsumer(bootstrapServers, "latest");
System.out.println("Subscribed to topic: " + readFromKafka);
consumer.subscribe(Collections.singletonList(readFromKafka));
long started = System.currentTimeMillis();
while (!needStop.get()) {
assignment.set(consumer.assignment());
ConsumerRecords<String, byte[]> records = consumer.poll(1_000);
events.addAll(CommonUtils4Tst.readEvents(records));
if (readTimeout == -1) {
if (events.size() > 0) {
break;
}
} else if (System.currentTimeMillis() - started > readTimeout) {
break;
}
}
needStop.set(true);
synchronized (MainTest.class) {
MainTest.class.notifyAll();
}
consumer.close();
}
P.S.
needStop - global flag, to stop all running thread if any in case of failure of success
events - list of object, that i want to check
readTimeout - how much time we will wait until read all data, if readTimeout == -1, then stop when we read anything
Thanks to Alexey (I have also voted up), I seemed to have resolved my issue essentially following the same idea.
Just want to share my experience... in our case we using Kafka in request & response way, somewhat like RPC. Request is being sent on one topic and then waiting for response on another topic. Running into a similar issue i.e. missing out first response.
I have tried ... KafkaConsumer.assignment(); repeatedly (with Thread.sleep(100);) but doesn't seem to help. Adding a KafkaConsumer.poll(50); seems to have primed the consumer (group) and receiving the first response too. Tested few times and it consistently working now.
BTW, testing requires stopping application & deleting Kafka topics and, for a good measure, restarted Kafka too.
PS: Just calling poll(50); without assignment(); fetching logic, like Alexey mentioned, may not guarantee that consumer (group) is ready.
You can modify an AlwaysSeekToEndListener (listens only to new messages) to include a callback:
public class AlwaysSeekToEndListener<K, V> implements ConsumerRebalanceListener {
private final Consumer<K, V> consumer;
private Runnable callback;
public AlwaysSeekToEndListener(Consumer<K, V> consumer) {
this.consumer = consumer;
}
public AlwaysSeekToEndListener(Consumer<K, V> consumer, Runnable callback) {
this.consumer = consumer;
this.callback = callback;
}
#Override
public void onPartitionsRevoked(Collection<TopicPartition> partitions) {
}
#Override
public void onPartitionsAssigned(Collection<TopicPartition> partitions) {
consumer.seekToEnd(partitions);
if (callback != null) {
callback.run();
}
}
}
and subscribe with a latch callback:
CountDownLatch initLatch = new CountDownLatch(1);
consumer.subscribe(singletonList(topic), new AlwaysSeekToEndListener<>(consumer, () -> initLatch.countDown()));
initLatch.await(); // blocks until consumer is ready and listening
then proceed to start your producer.
If your policy is set to latest - which takes effect if there are no previously committed offsets - but you have no previously committed offsets, then you should not worry about 'missing' messages, because you're telling Kafka not to care about messages that were sent 'previously' to your consumers being ready.
If you care about 'previous' messages, you should set the policy to earliest.
In any case, whatever the policy, the behaviour you are seeing is transient, i.e. once committed offsets are saved in Kafka, on every restart the consumers will pick up where they left previoulsy
I needed to know if a kafka consumer was ready before doing some testing, so i tried with consumer.assignment(), but it only returned the set of partitions assigned, but there was a problem, with this i cannot see if this partitions assigned to the group had offset setted, so later when i tried to use the consumer it didn´t have offset setted correctly.
The solutions was to use committed(), this will give you the last commited offsets of the given partitions that you put in the arguments.
So you can do something like: consumer.committed(consumer.assignment())
If there is no partitions assigned yet it will return:
{}
If there is partitions assigned, but no offset yet:
{name.of.topic-0=null, name.of.topic-1=null}
But if there is partitions and offset:
{name.of.topic-0=OffsetAndMetadata{offset=5197881, leaderEpoch=null, metadata=''}, name.of.topic-1=OffsetAndMetadata{offset=5198832, leaderEpoch=null, metadata=''}}
With this information you can use something like:
consumer.committed(consumer.assignment()).isEmpty();
consumer.committed(consumer.assignment()).containsValue(null);
And with this information you can be sure that the kafka consumer is ready.
If I have a enable.auto.commit=false and I call consumer.poll() without calling consumer.commitAsync() after, why does consumer.poll() return
new records the next time it's called?
Since I did not commit my offset, I would expect poll() would return the latest offset which should be the same records again.
I'm asking because I'm trying to handle failure scenarios during my processing. I was hoping without committing the offset, the poll() would return the same records again so I can re-process those failed records again.
public class MyConsumer implements Runnable {
#Override
public void run() {
while (true) {
ConsumerRecords<String, LogLine> records = consumer.poll(Long.MAX_VALUE);
for (ConsumerRecord record : records) {
try {
//process record
consumer.commitAsync();
} catch (Exception e) {
}
/**
If exception happens above, I was expecting poll to return new records so I can re-process the record that caused the exception.
**/
}
}
}
}
The starting offset of a poll is not decided by the broker but by the consumer. The consumer tracks the last received offset and asks for the following bunch of messages during the next poll.
Offset commits come into play when a consumer stops or fails and another instance that is not aware of the last consumed offset picks up consumption of a partition.
KafkaConsumer has pretty extensive Javadoc that is well worth a read.
Consumer will read from last commit offset if it get re balanced (means if any consumer leave the group or new consumer added) so handling de-duplication does not come straight forward in kafka so you have to store the last process offset in external store and when rebalance happens or app restart you should seek to that offset and start processing or you should check against some unique key in message against DB to find is dublicate
I would like to share some code how you can solve this in Java code.
The approach is that you poll the records, try to process them and if an exception occurs, you seek to the minima of the topic partitions. After that, you do the commitAsync().
public class MyConsumer implements Runnable {
#Override
public void run() {
while (true) {
List<ConsumerRecord<String, LogLine>> records = StreamSupport
.stream( consumer.poll(Long.MAX_VALUE).spliterator(), true )
.collect( Collectors.toList() );
boolean exceptionRaised = false;
for (ConsumerRecord<String, LogLine> record : records) {
try {
// process record
} catch (Exception e) {
exceptionRaised = true;
break;
}
}
if( exceptionRaised ) {
Map<TopicPartition, Long> offsetMinimumForTopicAndPartition = records
.stream()
.collect( Collectors.toMap( r -> new TopicPartition( r.topic(), r.partition() ),
ConsumerRecord::offset,
Math::min
) );
for( Map.Entry<TopicPartition, Long> entry : offsetMinimumForTopicAndPartition.entrySet() ) {
consumer.seek( entry.getKey(), entry.getValue() );
}
}
consumer.commitAsync();
}
}
}
With this setup, you poll the messages again and again until you successfully process all messages of one poll.
Please note, that your code should be able to handle a poison pill. Otherwise, your code will stuck in an endless loop.
I have a requirement where there are 2 topics to be maintained 1 with synchronous approach and other with an asynchronous way.
The asynchronous works as expected invoking the consumer record, however in the synchronous approach the consumer code is not getting invoked.
Below is the code declared in the config file
props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9093");
props.put(ProducerConfig.RETRIES_CONFIG, 3);
props.put(ProducerConfig.BATCH_SIZE_CONFIG, 16384);
props.put(ProducerConfig.ACKS_CONFIG, "all");
props.put(ProducerConfig.LINGER_MS_CONFIG, 1);
props.put(ProducerConfig.BUFFER_MEMORY_CONFIG, 33554432);
I have enabled autoFlush true here
#Bean( name="KafkaPayloadSyncTemplate")
public KafkaTemplate<String, KafkaPayload> KafkaPayloadSyncTemplate() {
return new KafkaTemplate<String,KafkaPayload>(producerFactory(),true);
}
The control stops thereafter not making any calls to the consumer after returning the recordMetadataResults object
private List<RecordMetadata> sendPayloadToKafkaTopicInSync() throws InterruptedException, ExecutionException {
final List<RecordMetadata> recordMetadataResults = new ArrayList<RecordMetadata>();
KafkaPayload kafkaPayload = constructKafkaPayload();
ListenableFuture<SendResult<String,KafkaPayload>>
future = KafkaPayloadSyncTemplate.send(TestTopic, kafkaPayload);
SendResult<String, KafkaPayload> results;
results = future.get();
recordMetadataResults.add(results.getRecordMetadata());
return recordMetadataResults;
}
Consumer Code
public class KafkaTestListener {
#Autowired
TestServiceImpl TestServiceImpl;
public final CountDownLatch countDownLatch = new CountDownLatch(1);
#KafkaListener(id="POC", topics = "TestTopic", group = "TestGroup")
public void listen(ConsumerRecord<String,KafkaPayload> record, Acknowledgment acknowledgment) {
countDownLatch.countDown();
TestServiceImpl.consumeKafkaMessage(record);
System.out.println("Acknowledgment : " + acknowledgment);
acknowledgment.acknowledge();
}
}
Based on the issue, I have 2 questions
Should we manually call the listen() inside the Listener Class when its a Sync Producer. If Yes, How to do that ?
If the listener(#KafkaListener) get called automatically, what other setup/configurations do I need to add to make this working.
Thanks for the inputs in advance
-Srikant
You should be sure that you use consumerProps.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest"); for Consumer Properties.
Not sure what you mean about sync/async, but produce and consume are fully distinguished operations. And you can't affect consumer from your producer side. Because in between there is Kafka Broker.