FSImage writing should always fsync before close
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Key: HDFS-970
URL: https://issues.apache.org/jira/browse/HDFS-970
Project: Hadoop HDFS
Issue Type: Bug
Components: name-node
Affects Versions: 0.20.1, 0.21.0, 0.22.0
Reporter: Todd Lipcon
Assignee: Todd Lipcon
Priority: Critical
Without an fsync, it's common that filesystems will delay the writing of
metadata to the journal until all of the data blocks have been flushed. If the
system crashes while the dirty pages haven't been flushed, the file is left in
an indeterminate state. In some FSs (eg ext4) this will result in a 0-length
file. In others (eg XFS) it will result in the correct length but any number of
data blocks getting zeroed. Calling FileChannel.force before closing the
FSImage prevents this issue.
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