Failed block replication leaves an incomplete block in receiver's tmp data
directory
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Key: HADOOP-4702
URL: https://issues.apache.org/jira/browse/HADOOP-4702
Project: Hadoop Core
Issue Type: Bug
Components: dfs
Affects Versions: 0.17.2
Reporter: Hairong Kuang
Fix For: 0.20.0
When a failure occurs while replicating a block from a source DataNode to a
target DataNode, the target node keeps an incomplete on-disk copy of the block
in its temp data directory and an in-memory copy of the block in ongoingCreates
queue. This causes two problems:
1. Since this block is not (should not) be finalized, NameNode is not aware of
the existence of this incomplete block. It may schedule replicating the same
block to this node again, which will fail with a message: "Block XX has already
been started (though not completed), and thus cannot be created."
2. Restarting the datanode moves the blocks under the temp data directory to be
valid blocks, thus introduces corrupted blocks into HDFS. Sometimes those
corrupted blocks stay in the system undetected if it happens that the partial
block and its checksums match.
A failed block replication should clean up both the in-memory & on-disk copies
of the incomplete block.
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