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https://issues.apache.org/jira/browse/HDFS-17342?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17811794#comment-17811794
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ASF GitHub Bot commented on HDFS-17342:
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zhangshuyan0 commented on PR #6464:
URL: https://github.com/apache/hadoop/pull/6464#issuecomment-1914338798
Hi @smarthanwang , do you have any further comments on this PR?
> Fix DataNode may invalidates normal block causing missing block
> ---------------------------------------------------------------
>
> Key: HDFS-17342
> URL: https://issues.apache.org/jira/browse/HDFS-17342
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Reporter: Haiyang Hu
> Assignee: Haiyang Hu
> Priority: Major
> Labels: pull-request-available
> Fix For: 3.5.0
>
>
> When users read an append file, occasional exceptions may occur, such as
> org.apache.hadoop.hdfs.BlockMissingException: Could not obtain block: xxx.
> This can happen if one thread is reading the block while writer thread is
> finalizing it simultaneously.
> *Root cause:*
> # The reader thread obtains a RBW replica from VolumeMap, such as:
> blk_xxx_xxx[RBW] and the data file should be in /XXX/rbw/blk_xxx.
> # Simultaneously, the writer thread will finalize this block, moving it from
> the RBW directory to the FINALIZE directory. the data file is move from
> /XXX/rbw/block_xxx to /XXX/finalize/block_xxx.
> # The reader thread attempts to open this data input stream but encounters a
> FileNotFoundException because the data file /XXX/rbw/blk_xxx or meta file
> /XXX/rbw/blk_xxx_xxx doesn't exist at this moment.
> # The reader thread will treats this block as corrupt, removes the replica
> from the volume map, and the DataNode reports the deleted block to the
> NameNode.
> # The NameNode removes this replica for the block.
> # If the current file replication is 1, this file will cause a missing block
> issue until this DataNode executes the DirectoryScanner again.
> As described above, when the reader thread encountered FileNotFoundException
> is as expected, because the file is moved.
> So we need to add a double check to the invalidateMissingBlock logic to
> verify whether the data file or meta file exists to avoid similar cases.
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