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From "Ravi Prakash (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9205) Do not schedule corrupt blocks for replication
Date Wed, 24 Aug 2016 23:01:20 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15435895#comment-15435895
] 

Ravi Prakash commented on HDFS-9205:
------------------------------------

Thanks for the change Nicholas! Should this line be modified? https://github.com/apache/hadoop/blob/a1f3293762dddb0ca953d1145f5b53d9086b25b8/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/LowRedundancyBlocks.java#L62
.

I think most often this queue had missing blocks, so it didn't really make sense to re-replicate
missing blocks anyway. We should be careful about removing this queue though, because its
where the [count of missing blocks is taken from|https://github.com/apache/hadoop/blob/a1f3293762dddb0ca953d1145f5b53d9086b25b8/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java#L4112]

> Do not schedule corrupt blocks for replication
> ----------------------------------------------
>
>                 Key: HDFS-9205
>                 URL: https://issues.apache.org/jira/browse/HDFS-9205
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>            Reporter: Tsz Wo Nicholas Sze
>            Assignee: Tsz Wo Nicholas Sze
>            Priority: Minor
>             Fix For: 2.8.0
>
>         Attachments: h9205_20151007.patch, h9205_20151007b.patch, h9205_20151008.patch,
h9205_20151009.patch, h9205_20151009b.patch, h9205_20151013.patch, h9205_20151015.patch
>
>
> Corrupted blocks by definition are blocks cannot be read. As a consequence, they cannot
be replicated.  In UnderReplicatedBlocks, there is a queue for QUEUE_WITH_CORRUPT_BLOCKS and
chooseUnderReplicatedBlocks may choose blocks from it.  It seems that scheduling corrupted
block for replication is wasting resource and potentially slow down replication for the higher
priority blocks.



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