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https://issues.apache.org/jira/browse/KAFKA-4893?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15927038#comment-15927038
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Ismael Juma commented on KAFKA-4893:
------------------------------------
Adding directories introduces more complexity due to fsync semantics. See
KAFKA-3968.
> async topic deletion conflicts with max topic length
> ----------------------------------------------------
>
> Key: KAFKA-4893
> URL: https://issues.apache.org/jira/browse/KAFKA-4893
> Project: Kafka
> Issue Type: Bug
> Reporter: Onur Karaman
> Assignee: Vahid Hashemian
> Priority: Minor
>
> As per the
> [documentation|http://kafka.apache.org/documentation/#basic_ops_add_topic],
> topics can be only 249 characters long to line up with typical filesystem
> limitations:
> {quote}
> Each sharded partition log is placed into its own folder under the Kafka log
> directory. The name of such folders consists of the topic name, appended by a
> dash (\-) and the partition id. Since a typical folder name can not be over
> 255 characters long, there will be a limitation on the length of topic names.
> We assume the number of partitions will not ever be above 100,000. Therefore,
> topic names cannot be longer than 249 characters. This leaves just enough
> room in the folder name for a dash and a potentially 5 digit long partition
> id.
> {quote}
> {{kafka.common.Topic.maxNameLength}} is set to 249 and is used during
> validation.
> This limit ends up not being quite right since topic deletion ends up
> renaming the directory to the form {{topic-partition.uniqueId-delete}} as can
> be seen in {{LogManager.asyncDelete}}:
> {code}
> val dirName = new StringBuilder(removedLog.name)
> .append(".")
>
> .append(java.util.UUID.randomUUID.toString.replaceAll("-",""))
> .append(Log.DeleteDirSuffix)
> .toString()
> {code}
> So the unique id and "-delete" suffix end up hogging some of the characters.
> Deleting a long-named topic results in a log message such as the following:
> {code}
> kafka.common.KafkaStorageException: Failed to rename log directory from
> /tmp/kafka-logs0/000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000-0
> to
> /tmp/kafka-logs0/000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000-0.797bba3fb2464729840f87769243edbb-delete
> at kafka.log.LogManager.asyncDelete(LogManager.scala:439)
> at
> kafka.cluster.Partition$$anonfun$delete$1.apply$mcV$sp(Partition.scala:142)
> at kafka.cluster.Partition$$anonfun$delete$1.apply(Partition.scala:137)
> at kafka.cluster.Partition$$anonfun$delete$1.apply(Partition.scala:137)
> at kafka.utils.CoreUtils$.inLock(CoreUtils.scala:213)
> at kafka.utils.CoreUtils$.inWriteLock(CoreUtils.scala:221)
> at kafka.cluster.Partition.delete(Partition.scala:137)
> at kafka.server.ReplicaManager.stopReplica(ReplicaManager.scala:230)
> at
> kafka.server.ReplicaManager$$anonfun$stopReplicas$2.apply(ReplicaManager.scala:260)
> at
> kafka.server.ReplicaManager$$anonfun$stopReplicas$2.apply(ReplicaManager.scala:259)
> at scala.collection.Iterator$class.foreach(Iterator.scala:727)
> at scala.collection.AbstractIterator.foreach(Iterator.scala:1157)
> at scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
> at scala.collection.AbstractIterable.foreach(Iterable.scala:54)
> at kafka.server.ReplicaManager.stopReplicas(ReplicaManager.scala:259)
> at kafka.server.KafkaApis.handleStopReplicaRequest(KafkaApis.scala:174)
> at kafka.server.KafkaApis.handle(KafkaApis.scala:86)
> at kafka.server.KafkaRequestHandler.run(KafkaRequestHandler.scala:64)
> at java.lang.Thread.run(Thread.java:745)
> {code}
> The topic after this point still exists but has Leader set to -1 and the
> controller recognizes the topic completion as incomplete (the topic znode is
> still in /admin/delete_topics).
> I don't believe linkedin has any topic name this long but I'm making the
> ticket in case anyone runs into this problem.
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