[jira] [Created] (HDFS-4596) Shutting down namenode during checkpointing can lead to md5sum error

["Andrew Wang (JIRA)" <ji...@apache.org>]

Andrew Wang created HDFS-4596:
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             Summary: Shutting down namenode during checkpointing can lead to md5sum error
                 Key: HDFS-4596
                 URL: https://issues.apache.org/jira/browse/HDFS-4596
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: namenode
    Affects Versions: 3.0.0
            Reporter: Andrew Wang
            Assignee: Andrew Wang
             Fix For: 2.0.4-alpha


This is a really rare error that can hit if a NN shutdown happens during the checkpointing process.

Checkpointing and restarting nominally looks like this:

# FSImage is written to a tmp file and then renamed
# MD5 file is written to a tmp file and then renamed
# NN is killed and restarted
# NN scans storage directories and picks up the renamed image file
# NN validates that the image file matches its md5 file

If the NN is killed before step 2 completes, this is what happens:

# FSImage is written to a tmp file and then renamed
# NN is killed and restarted (no MD5 file!)
# NN scans storage directories and picks up the renamed image file
# Since there's no matching MD5 file, NN errors out with a checksum error

I think we can fix this by inverting the order of writing the image then md5, or inverting the order of reading the image then md5.

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