Is there a way to delete all the data from a topic

Question

Is there a way to delete all the data from a topic or delete the topic before every run?

Can I modify the KafkaConfig.scala file to change the logRetentionHours property? Is there a way the messages gets deleted as soon as the consumer reads it?

I am using producers to fetch the data from somewhere and sending the data to a particular topic where a consumer consumes, can I delete all the data from that topic on every run? I want only new data every time in the topic. Is there a way to reinitialize the topic somehow?

Answer 1

1. Stop ZooKeeper and Kafka
2. In server.properties, change log.retention.hours value. You can comment log.retention.hours and add log.retention.ms=1000. It would keep the record on Kafka Topic for only one second.
3. Start zookeeper and kafka.
4. Check on consumer console. When I opened the console for the first time, record was there. But when I opened the console again, the record was removed.
5. Later on, you can set the value of log.retention.hours to your desired figure.

Answer 2

Don't think it is supported yet. Take a look at this JIRA issue "Add delete topic support".

To delete manually:

1. Shutdown the cluster
2. Clean kafka log dir (specified by the log.dir attribute in kafka config file ) as well the zookeeper data
3. Restart the cluster

For any given topic what you can do is

1. Stop kafka
2. Clean kafka log specific to partition, kafka stores its log file in a format of "logDir/topic-partition" so for a topic named "MyTopic" the log for partition id 0 will be stored in /tmp/kafka-logs/MyTopic-0 where /tmp/kafka-logs is specified by the log.dir attribute
3. Restart kafka

This is NOT a good and recommended approach but it should work. In the Kafka broker config file the log.retention.hours.per.topic attribute is used to define The number of hours to keep a log file before deleting it for some specific topic

Also, is there a way the messages gets deleted as soon as the consumer reads it?

From the Kafka Documentation :

The Kafka cluster retains all published messages—whether or not they have been consumed—for a configurable period of time. For example if the log retention is set to two days, then for the two days after a message is published it is available for consumption, after which it will be discarded to free up space. Kafka's performance is effectively constant with respect to data size so retaining lots of data is not a problem.

In fact the only metadata retained on a per-consumer basis is the position of the consumer in in the log, called the "offset". This offset is controlled by the consumer: normally a consumer will advance its offset linearly as it reads messages, but in fact the position is controlled by the consumer and it can consume messages in any order it likes. For example a consumer can reset to an older offset to reprocess.

For finding the start offset to read in Kafka 0.8 Simple Consumer example they say

Kafka includes two constants to help, kafka.api.OffsetRequest.EarliestTime() finds the beginning of the data in the logs and starts streaming from there, kafka.api.OffsetRequest.LatestTime() will only stream new messages.

You can also find the example code there for managing the offset at your consumer end.

    public static long getLastOffset(SimpleConsumer consumer, String topic, int partition,
                                 long whichTime, String clientName) {
    TopicAndPartition topicAndPartition = new TopicAndPartition(topic, partition);
    Map<TopicAndPartition, PartitionOffsetRequestInfo> requestInfo = new HashMap<TopicAndPartition, PartitionOffsetRequestInfo>();
    requestInfo.put(topicAndPartition, new PartitionOffsetRequestInfo(whichTime, 1));
    kafka.javaapi.OffsetRequest request = new kafka.javaapi.OffsetRequest(requestInfo, kafka.api.OffsetRequest.CurrentVersion(),clientName);
    OffsetResponse response = consumer.getOffsetsBefore(request);

    if (response.hasError()) {
        System.out.println("Error fetching data Offset Data the Broker. Reason: " + response.errorCode(topic, partition) );
        return 0;
    }
    long[] offsets = response.offsets(topic, partition);
    return offsets[0];
}

Answer 3

As a dirty workaround, you can adjust per-topic runtime retention settings, e.g. bin/kafka-topics.sh --zookeeper localhost:2181 --alter --topic my_topic --config retention.bytes=1 (retention.bytes=0 might also work)

After a short while kafka should free the space. Not sure if this has any implications compared to re-creating the topic.

ps. Better bring retention settings back, once kafka done with cleaning.

You can also use retention.ms to persist historical data

Answer 4

Tested with kafka 0.10

1. stop zookeeper & Kafka server,
2. then go to 'kafka-logs' folder , there you will see list of kafka topic folders, delete folder with topic name
3. go to 'zookeeper-data' folder , delete data inside that.
4. start zookeeper & kafka server again.

Note : if you are deleting topic folder/s inside kafka-logs but not from zookeeper-data folder, then you will see topics are still there.

Answer 5

For brew users

If you're using brew like me and wasted a lot of time searching for the infamous kafka-logs folder, fear no more. (and please do let me know if that works for you and multiple different versions of Homebrew, Kafka etc :) )

You're probably going to find it under:

Location:

/usr/local/var/lib/kafka-logs

---

How to actually find that path

(this is also helpful for basically every app you install through brew)

1) brew services list

kafka started matbhz /Users/matbhz/Library/LaunchAgents/homebrew.mxcl.kafka.plist

2) Open and read that plist you found above

3) Find the line defining server.properties location open it, in my case:

• /usr/local/etc/kafka/server.properties

4) Look for the log.dirs line:

log.dirs=/usr/local/var/lib/kafka-logs

5) Go to that location and delete the logs for the topics you wish

6) Restart Kafka with brew services restart kafka

Answer 6

As I mentioned here Purge Kafka Queue:

Tested in Kafka 0.8.2, for the quick-start example: First, Add one line to server.properties file under config folder:

delete.topic.enable=true

then, you can run this command:

bin/kafka-topics.sh --zookeeper localhost:2181 --delete --topic test