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From "Walter Su (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10301) Blocks removed by thousands due to falsely detected zombie storages
Date Tue, 19 Apr 2016 02:17:25 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10301?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15246996#comment-15246996

Walter Su commented on HDFS-10301:

1. IPC reader is single-thread by default. If it's multi-threaded, The order of putting rpc
requests into {{callQueue}} is unspecified.
1. IPC {{callQueue}} is fifo.
2. IPC Handler is multi-threaded. If 2 handlers are both waiting the fsn lock, the entry order
depends on the fairness of the lock.
bq. When constructed as fair, threads contend for entry using an *approximately* arrival-order
policy. When the currently held lock is released either the longest-waiting single writer
thread will be assigned the write lock... (quore from https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/locks/ReentrantReadWriteLock.html)

I think if DN can't get acked from NN, it shouldn't assume the arrival/processing order(esp
when reestablish a connection). Well, I'm still curious about how the interleave happened.
Any thoughts?

> Blocks removed by thousands due to falsely detected zombie storages
> -------------------------------------------------------------------
>                 Key: HDFS-10301
>                 URL: https://issues.apache.org/jira/browse/HDFS-10301
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.6.1
>            Reporter: Konstantin Shvachko
>            Priority: Critical
>         Attachments: zombieStorageLogs.rtf
> When NameNode is busy a DataNode can timeout sending a block report. Then it sends the
block report again. Then NameNode while process these two reports at the same time can interleave
processing storages from different reports. This screws up the blockReportId field, which
makes NameNode think that some storages are zombie. Replicas from zombie storages are immediately
removed, causing missing blocks.

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