NameNode should send both both replication and deletion requests to DataNode in
one reply to a heartbeat
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Key: HADOOP-5034
URL: https://issues.apache.org/jira/browse/HADOOP-5034
Project: Hadoop Core
Issue Type: New Feature
Components: dfs
Reporter: Hairong Kuang
Fix For: 0.21.0
Currently NameNode favors block replication requests over deletion requests. On
reply to a heartbeat, NameNode does not send a block deletion request unless
there is no block replication request.
This brings a problem when a near-full cluster loses a bunch of DataNodes. In
react to the DataNode loss, NameNode starts to replicate blocks. However,
replication takes a lot of cpu and a lot of replications fail because of the
lack of disk space. So the administrator tries to delete some DFS files to free
up space. However, block deletion requests get delayed for very long time
because it takes a long time to drain the block replication requests for most
DataNodes.
I'd like to propose to let NameNode to send both replication requests and
deletion requests to DataNodes in one reply to a heartbeat. This also implies
that the replication monitor should schedule both replication and deletion work
in one iteration.
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