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https://issues.apache.org/jira/browse/HADOOP-1649?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12517096
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Raghu Angadi commented on HADOOP-1649:
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bq. Digressing from this jira little bit.. Namenode does not need to track this
information. Datanode can report 'active write/reads' in its heartbeat and
namenode can give preference to the datanodes that have less active
transactions in chooseTarget().
The load is already considered in DFS.
> Performance regression with Block CRCs
> --------------------------------------
>
> Key: HADOOP-1649
> URL: https://issues.apache.org/jira/browse/HADOOP-1649
> Project: Hadoop
> Issue Type: Bug
> Affects Versions: 0.14.0
> Reporter: Raghu Angadi
> Assignee: Raghu Angadi
> Priority: Blocker
> Fix For: 0.14.0
>
> Attachments: HADOOP-1649.patch
>
>
> Performance is noticeably affected by Block Level CRCs patch (HADOOP-1134).
> This is more noticeable on writes (randomriter test etc).
> With random writer, it takes 20-25% on small cluster (20 nodes) and many be
> 10% on larger cluster.
> There are a few differences in how data is written with 1134. As soon as I
> can reproduce this, I think it will be easier to fix.
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