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From "Brian Nixon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-3240) Close socket on Learner shutdown to avoid dangling socket
Date Thu, 10 Jan 2019 20:20:00 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-3240?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16739750#comment-16739750

Brian Nixon commented on ZOOKEEPER-3240:

This may be the same issue as detected in ZOOKEEPER-2669. The two share certain similarities
but I haven't looked into it.

> Close socket on Learner shutdown to avoid dangling socket
> ---------------------------------------------------------
>                 Key: ZOOKEEPER-3240
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3240
>             Project: ZooKeeper
>          Issue Type: Improvement
>          Components: server
>    Affects Versions: 3.6.0
>            Reporter: Brian Nixon
>            Priority: Minor
> There was a Learner that had two connections to the Leader after that Learner hit an
unexpected exception during flush txn to disk, which will shutdown previous follower instance
and restart a new one.
> {quote}2018-10-26 02:31:35,568 ERROR [SyncThread:3:ZooKeeperCriticalThread@48] - Severe
unrecoverable error, from thread : SyncThread:3
> java.io.IOException: Input/output error
>         at java.base/sun.nio.ch.FileDispatcherImpl.force0(Native Method)
>         at java.base/sun.nio.ch.FileDispatcherImpl.force(FileDispatcherImpl.java:72)
>         at java.base/sun.nio.ch.FileChannelImpl.force(FileChannelImpl.java:395)
>         at org.apache.zookeeper.server.persistence.FileTxnLog.commit(FileTxnLog.java:457)
>         at org.apache.zookeeper.server.persistence.FileTxnSnapLog.commit(FileTxnSnapLog.java:548)
>         at org.apache.zookeeper.server.ZKDatabase.commit(ZKDatabase.java:769)
>         at org.apache.zookeeper.server.SyncRequestProcessor.flush(SyncRequestProcessor.java:246)
>         at org.apache.zookeeper.server.SyncRequestProcessor.run(SyncRequestProcessor.java:172)
> 2018-10-26 02:31:35,568 INFO  [SyncThread:3:ZooKeeperServerListenerImpl@42] - Thread
SyncThread:3 exits, error code 1
> 2018-10-26 02:31:35,568 INFO [SyncThread:3:SyncRequestProcessor@234] - SyncRequestProcessor
> It is supposed to close the previous socket, but it doesn't seem to be done anywhere
in the code. This leaves the socket open with no one reading from it, and caused the queue
full and blocked on sender.
> Since the LearnerHandler didn't shutdown gracefully, the learner queue size keeps growing,
the JVM heap size on leader keeps growing and added pressure to the GC, and cause high GC
time and latency in the quorum.
> The simple fix is to gracefully shutdown the socket.

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