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https://issues.apache.org/jira/browse/HDFS-7784?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14320201#comment-14320201
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Walter Su commented on HDFS-7784:
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I agree with you. A single Namenode with 64GB memory can hold about 100m
files(maybe a little more). In this situation, The startup time drops from 371s
to 159s and it's not good enough. Usually we don't restart Namenode often. So I
think it's ok we wait another 2 minutes for restarting.
If people store 10x or 100x more than 100m files, they should consider
federation.
So I changed the priority to minor, and still I'll upload the patch, Maybe
it'll help someone.
> load fsimage in parallel
> ------------------------
>
> Key: HDFS-7784
> URL: https://issues.apache.org/jira/browse/HDFS-7784
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Reporter: Walter Su
> Assignee: Walter Su
> Priority: Minor
> Attachments: HDFS-7784.001.patch, test-20150213.pdf
>
>
> When single Namenode has huge amount of files, without using federation, the
> startup/restart speed is slow. The fsimage loading step takes the most of the
> time. fsimage loading can seperate to two parts, deserialization and object
> construction(mostly map insertion). Deserialization takes the most of CPU
> time. So we can do deserialization in parallel, and add to hashmap in serial.
> It will significantly reduce the NN start time.
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