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From "Todd Lipcon (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-3023) Optimize entries in edits log for persistBlocks calls
Date Tue, 28 Feb 2012 04:58:48 GMT
Optimize entries in edits log for persistBlocks calls
-----------------------------------------------------

                 Key: HDFS-3023
                 URL: https://issues.apache.org/jira/browse/HDFS-3023
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: name-node, performance
    Affects Versions: HA branch (HDFS-1623), 0.23.2
            Reporter: Todd Lipcon
            Assignee: Todd Lipcon


One of the performance issues noticed in the HA branch is due to the much larger edit logs,
now that we are writing OP_ADD transactions to the edit log on every block allocation. We
can condense these calls down in two ways:
1) use variable-length integers for the block list length, size, and genstamp (most of these
end up fitting in far less than 8 bytes)
2) use delta-coding for the genstamp and block size for any blocks after the first block (most
blocks will be the same size and only slightly higher genstamps)
3) introduce a new OP_UPDATE_BLOCKS transaction that doesn't re-serialize metadata information
like lease owner, permissions, etc
4) allow OP_UPDATE_BLOCKS to only re-serialize the blocks that have changed for a given transaction

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