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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1391) Exiting safemode takes a long time when there are lots of blocks in the HDFS
Date Mon, 20 Sep 2010 21:51:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12912733#action_12912733
] 

Konstantin Shvachko commented on HDFS-1391:
-------------------------------------------

> Thus, exiting safemode is fast, thereby reducing the time to restart the namenode.

How much faster? It would be good to have some numbers for comparison.

> Exiting safemode takes a long time when there are lots of blocks in the HDFS
> ----------------------------------------------------------------------------
>
>                 Key: HDFS-1391
>                 URL: https://issues.apache.org/jira/browse/HDFS-1391
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: excessReplicas.1_trunk.txt
>
>
> When the namenode decides to exit safemode,  it acquires the FSNamesystem lock and then
iterates over all blocks in the blocksmap to determine if any block has any excess replicas.
This call takes upwards of 5 minutes on a cluster that has 100 million blocks. This delays
namenode restart to a good extent.

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