Slow generation of blockReport at DataNode causes delay of sending heartbeat to
NameNode
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Key: HADOOP-4584
URL: https://issues.apache.org/jira/browse/HADOOP-4584
Project: Hadoop Core
Issue Type: Bug
Reporter: Hairong Kuang
Fix For: 0.20.0
sometimes due to disk or some other problems, datanode takes minutes or tens of
minutes to generate a block report. It causes the datanode not able to send
heartbeat to NameNode every 3 seconds. In the worst case, it makes NameNode to
detect a lost heartbeat and wrongly decide that the datanode is dead.
It would be nice to have two threads instead. One thread is for scanning data
directories and generating block report, and executes the requests sent by
NameNode; Another thread is for sending heartbeats, block reports, and picking
up the requests from NameNode. By having these two threads, the sending of
heartbeats will not get delayed by any slow block report or slow execution of
NameNode requests.
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