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From "Mingliang Liu (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-10201) Implement undo log in parity datanode for hflush operations
Date Wed, 23 Mar 2016 18:01:25 GMT
Mingliang Liu created HDFS-10201:
------------------------------------

             Summary: Implement undo log in parity datanode for hflush operations
                 Key: HDFS-10201
                 URL: https://issues.apache.org/jira/browse/HDFS-10201
             Project: Hadoop HDFS
          Issue Type: Sub-task
          Components: erasure-coding
            Reporter: Mingliang Liu
            Assignee: Mingliang Liu


According to the current design doc for hflush support in erasure coding (see [HDFS-7661]),
the parity datanode (DN) needs an undo log for flush operations. After hflush/hsync, the last
cell will be overwritten when 1) the current strip is full, 2) the file is closed, 3) or the
hflush/hsync is called again for the current non-full stripe. To serve new reader client and
to tolerate failures between successful hflush/hsync and overwrite operation, the parity DN
should preserve the old cell in the undo log before overwriting it.

As parities correspond to BG length and parity data of different BG length may have the same
block length, the undo log should also save the respective block group (BG) length information
for the flushed data.

This jira is to track the effort of designing and implementing an undo log in parity DN to
support hflush/hsync operations.



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