Name node is using the write-ahead log improperly
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Key: HDFS-1137
URL: https://issues.apache.org/jira/browse/HDFS-1137
Project: Hadoop HDFS
Issue Type: Bug
Components: name-node
Reporter: Benjamin Reed
The Name node is doing the write-ahead log (WAL) (aka edit log) improperly.
Usually when using WAL, changes are written to the log before they are applied
to the state. Currently the Namenode does the WAL after applying the change.
This means that read may see changes before they are durable. A client may read
information and the server fail before the information is written to the WAL,
which results in the client reading state that disappears. To fix the Namenode
should write changes before (aka ahead of) applying the change.
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