Daryn Sharp created HDFS-7967:
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Summary: Reduce the performance impact of the balancer
Key: HDFS-7967
URL: https://issues.apache.org/jira/browse/HDFS-7967
Project: Hadoop HDFS
Issue Type: Sub-task
Affects Versions: 2.0.0-alpha
Reporter: Daryn Sharp
Assignee: Daryn Sharp
The balancer needs to query for blocks to move from overly full DNs. The block
lookup is extremely inefficient. An iterator of the node's blocks is created
from the iterators of its storages' blocks. A random number is chosen
corresponding to how many blocks will be skipped via the iterator. Each skip
requires costly scanning of triplets.
The current design also only considers node imbalances while ignoring
imbalances within the nodes's storages. A more efficient and intelligent
design may eliminate the costly skipping of blocks via round-robin selection of
blocks from the storages based on remaining capacity.
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