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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1368) Add a block counter to DatanodeDescriptor
Date Sun, 05 Sep 2010 00:38:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1368?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12906314#action_12906314
] 

dhruba borthakur commented on HDFS-1368:
----------------------------------------

+1 , looks like a simple optimization to me.

> Add a block counter to DatanodeDescriptor
> -----------------------------------------
>
>                 Key: HDFS-1368
>                 URL: https://issues.apache.org/jira/browse/HDFS-1368
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>             Fix For: 0.22.0
>
>         Attachments: blockCounter.patch
>
>
> Many of time, we need to count the total number of blocks in a datanode by calling DatanodeDescriptor#numBlocks().
It has to traverse the block list to get the counter, which may not be trivial if there are
millions of blocks. Adding a counter for each datanode does not cost much space but help save
CPU processing time.

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