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  1. Hadoop HDFS
  2. HDFS-3023

Optimize entries in edits log for persistBlocks calls

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    Details

    • Type: Improvement
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: HA branch (HDFS-1623), 0.23.2
    • Fix Version/s: HA branch (HDFS-1623)
    • Component/s: namenode, performance
    • Labels:
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      Description

      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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