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https://issues.apache.org/jira/browse/HDFS-5443?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13808561#comment-13808561
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Brandon Li commented on HDFS-5443:
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{quote}...block wa allocated only in Namenode but pipeline not established to
DNs Yet, so, physical block is not created in Datanodes.{quote}
This happens too even when snapshot is not involved. But without capturing the
underconstruction file in snapshot, this problem is hard to notice.
{quote}Option 1) Why can't we save underconstuction boolan flag for all INode
as true or false.{quote}
This can increase memory usage. Underconstructed files are expected to be a
very small portion in the namespace.
{quote}Option 2) May be we have to deal snapshotted underconstruction files
with some special care here.{quote}
When the snapshot is taken, the block allocated but size is zero (no matter
it's because pipeline-not-created or sized-not-reported-yet). In this case, the
zero sized block may not need to be recorded in the snapshot at all.
> Namenode can stuck in safemode on restart if it crashes just after addblock
> logsync and after taking snapshot for such file.
> ----------------------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-5443
> URL: https://issues.apache.org/jira/browse/HDFS-5443
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: snapshots
> Affects Versions: 3.0.0, 2.2.0
> Reporter: Uma Maheswara Rao G
> Assignee: sathish
>
> This issue is reported by Prakash and Sathish.
> On looking into the issue following things are happening.
> .
> 1) Client added block at NN and just did logsync
> So, NN has block ID persisted.
> 2)Before returning addblock response to client take a snapshot for root or
> parent directories for that file
> 3) Delete parent directory for that file
> 4) Now crash the NN with out responding success to client for that addBlock
> call
> Now on restart of the Namenode, it will stuck in safemode.
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