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https://issues.apache.org/jira/browse/HADOOP-2159?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12598833#action_12598833
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Hairong Kuang commented on HADOOP-2159:
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Name Node keeps track of the total number of valid block it received in safe
mode. A valid block is a block that belongs to a file. The counter is called
blockSafe. The name node does not leave the safe mode automatically if the
ratio of blockSafe to the total number of valid blocks is less the threshold.
I see a bug in maintaining this counter. Before the counter is incremented,
the name node check if the block is valid. Before it does not do the check
before this counter is decremented.
When a dfs cluster is started, if an early started data node has stale blocks,
the name node will ask the data node to delete the stale blocks as the reply to
its first block report. If its second block report comes in when the name node
is still in safe mode, those blocks will be removed from the blocks map, and
the blockSafe counter will also be decremented even though those blocks are
invalid. So the cluster will end up with a blockSafe counter that's smaller
than the number of valid blocks in namenode. If the threshold is set to be 1,
the cluster will not be able to leave the safe mode.
> Namenode stuck in safemode
> --------------------------
>
> Key: HADOOP-2159
> URL: https://issues.apache.org/jira/browse/HADOOP-2159
> Project: Hadoop Core
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.16.0
> Reporter: Christian Kunz
>
> Occasionally (not easy to reproduce) the namenode does turn off safemode
> automatically, although fsck does not report any missing or under-replicated
> blocks (safemode threshold set to 1.0).
> At this moment I do not have any additional information which could help
> analyze the issue.
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