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From "Benjamin Reed (JIRA)" <j...@apache.org>
Subject [jira] Created: (HDFS-1137) Name node is using the write-ahead log improperly
Date Fri, 07 May 2010 23:51:49 GMT
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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