Chris Nauroth created HDFS-4811:
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Summary: race condition between 2 namenodes in standby that are
trying to checkpoint with one another can delete or corrupt a good fsimage
Key: HDFS-4811
URL: https://issues.apache.org/jira/browse/HDFS-4811
Project: Hadoop HDFS
Issue Type: Bug
Components: ha
Affects Versions: 3.0.0, 2.0.5-beta
Reporter: Chris Nauroth
The problem occurs under concurrent execution of the namenode running its own
checkpoint in {{StandbyCheckpointer}} in thread 1 while also getting a
checkpoint from a different namenode in {{GetImageServlet}} in thread 2. It is
possible for thread 2 to finish writing the checkpoint to the directory, but
then get suspended before it has a chance to rename it to its final destination
as an fsimage file. Then, thread 1 wakes up and starts writing its own data to
the checkpoint file. When thread 2 resumes, it then tries to rename the file
that thread 1 still holds open for writing. Depending on OS, this either moves
thread 1's incomplete checkpoint to fsimage, or it just outright deletes the
existing good fsimage until thread 1 finishes writing and renames.
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