Optimize entries in edits log for persistBlocks calls
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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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