Increase granularity of write operations in ReplicationMonitor thus reducing
contention for write lock
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Key: HDFS-2495
URL: https://issues.apache.org/jira/browse/HDFS-2495
Project: Hadoop HDFS
Issue Type: Sub-task
Reporter: Tomasz Nykiel
Assignee: Tomasz Nykiel
For processing blocks in ReplicationMonitor
(BlockManager.computeReplicationWork), we first obtain a list of blocks to be
replicated by calling chooseUnderReplicatedBlocks, and then for each block
which was found, we call computeReplicationWorkForBlock. The latter processes a
block in three stages, acquiring the writelock twice per call:
1. obtaining block related info (livenodes, srcnode, etc.) under lock
2. choosing target for replication
3. scheduling replication (under lock)
We would like to change this behaviour and decrease contention for the write
lock, by batching blocks and executing 1,2,3, for sets of blocks, rather than
for each one separately. This would decrease the number of writeLock to 2, from
2*numberofblocks.
Also, the info level logging can be pushed outside the writelock.
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