[HDFS-3023] Optimize entries in edits log for persistBlocks calls

• 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
• Target Version/s: HA branch (HDFS-1623)
• Hadoop Flags: Reviewed
• Assignee: Todd Lipcon
• Reporter: Todd Lipcon
• Created: 28/Feb/12 04:57
• Updated: 01/Mar/12 20:28
• Resolved: 01/Mar/12 00:37

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

Issue Links

• is related to: HDFS-3010 Get performance on HA branch to match trunk