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https://issues.apache.org/jira/browse/KAFKA-10723?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jun Rao resolved KAFKA-10723.
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Fix Version/s: 2.8.0
Resolution: Fixed
merged to trunk
> LogManager leaks internal thread pool activity during shutdown
> --------------------------------------------------------------
>
> Key: KAFKA-10723
> URL: https://issues.apache.org/jira/browse/KAFKA-10723
> Project: Kafka
> Issue Type: Bug
> Reporter: Kowshik Prakasam
> Assignee: Kowshik Prakasam
> Priority: Major
> Fix For: 2.8.0
>
>
> *TL;DR:*
> The asynchronous shutdown in {{LogManager}} has the shortcoming that if
> during shutdown any of the internal futures fail, then we do not always
> ensure that all futures are completed before {{LogManager.shutdown}} returns.
> As a result, despite the shut down completed message from KafkaServer is seen
> in the error logs, some futures continue to run from inside LogManager
> attempting to close the logs. This is misleading and it could possibly break
> the general rule of avoiding post-shutdown activity in the Broker.
> *Description:*
> When LogManager is shutting down, exceptions in log closure are handled
> [here|https://github.com/apache/kafka/blob/trunk/core/src/main/scala/kafka/log/LogManager.scala#L497-L501].
> However, this
> [line|https://github.com/apache/kafka/blob/trunk/core/src/main/scala/kafka/log/LogManager.scala#L502]
> in the finally clause shuts down the thread pools *asynchronously*. The
> code: _threadPools.foreach(.shutdown())_ initiates an orderly shutdown (for
> each thread pool) in which previously submitted tasks are executed, but no
> new tasks will be accepted (see javadoc link
> [here|https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ExecutorService.html#shutdown()])_._
> As a result, if there is an exception during log closure, some of the thread
> pools which are closing logs could be leaked and continue to run in the
> background, after the control returns to the caller (i.e. {{KafkaServer}}).
> As a result, even after the "shut down completed" message is seen in the
> error logs (originating from {{KafkaServer}} shutdown sequence), log closures
> continue to happen in the background, which is misleading.
>
> *Proposed options for fixes:*
> It seems useful that we maintain the contract with {{KafkaServer}} that after
> {{LogManager.shutdown}} is called once, all tasks that close the logs are
> guaranteed to have completed before the call returns. There are probably
> couple different ways to fix this:
> # Replace {{_threadPools.foreach(.shutdown())_ with
> _threadPools.foreach(.awaitTermination())_}}{{.}} This ensures that we wait
> for all threads to be shutdown before returning the {{_LogManager.shutdown_}}
> call.
> # Skip creating of checkpoint and clean shutdown file only for the affected
> directory if any of its futures throw an error. We continue to wait for all
> futures to complete for all directories. This can require some changes to
> [this for
> loop|https://github.com/apache/kafka/blob/trunk/core/src/main/scala/kafka/log/LogManager.scala#L481-L496],
> so that we wait for all futures to complete regardless of whether one of
> them threw an error.
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