Kafka describe topic command lists multiple topics description

Question

Running following command on topic my.topic.test gives description on both my.topic.test and my.topic_test (notice the dot and underscore difference in the names) topics.
Is that desired behavior or a bug (I would lean towards a bug)?

kafka-topics --describe --zookeeper my_zookeeper_ip:2181 --topic my.topic.test
Topic:my.topic.test        PartitionCount:4        ReplicationFactor:1     Configs:
    Topic: my.topic.test       Partition: 0    Leader: 2       Replicas: 2     Isr: 2
    Topic: my.topic.test       Partition: 1    Leader: 3       Replicas: 3     Isr: 3
    Topic: my.topic.test       Partition: 2    Leader: 4       Replicas: 4     Isr: 4
    Topic: my.topic.test       Partition: 3    Leader: 0       Replicas: 0     Isr: 0
Topic:my.topic_test        PartitionCount:5        ReplicationFactor:4     Configs:
    Topic: my.topic_test       Partition: 0    Leader: 4       Replicas: 3,4,5,1       Isr: 4,1,3
    Topic: my.topic_test       Partition: 1    Leader: 4       Replicas: 1,3,4 Isr: 4,1,3
    Topic: my.topic_test       Partition: 2    Leader: 4       Replicas: 4,2,5,3       Isr: 4,3,2
    Topic: my.topic_test       Partition: 3    Leader: 4       Replicas: 5,1,4 Isr: 4,1
    Topic: my.topic_test       Partition: 4    Leader: 1       Replicas: 5,1,3,0       Isr: 1,0,3

Answer 1

When run with --describe , kafka-topics accepts a regex for the --topic argument. In a regex, . matches any characters so you see the expected behaviour.

That said, kafka-topics prints a warning when creating a topic with dots or underscores and should have prevented creating 2 topics with such names as metrics would collide:

WARNING: Due to limitations in metric names, topics with a period ('.') or underscore ('_') could collide. To avoid issues it is best to use either, but not both.

How did you create the topics ?

Answer 2

first of all ,it's not bug. according to source-code of kafka-10.2 in topic part Kafka-source ,

  val legalChars = "[a-zA-Z0-9\\._\\-]"
  private val maxNameLength = 249
  private val rgx = new Regex(legalChars + "+")

max length of your topic-name can be 249 words,and its treats dot(.) and underscore( _ ) are treated equal.That is your topic name

my.topic.test, my.topic_test, my_topic.test are same . you should either use ( _ )underscore or dot ( . ) but not both.

for best practice i'll recommend you to use hyphen ( - ) like i prefer to use.