nkeywal created HDFS-3703:
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Summary: Decrease the datanode failure detection time
Key: HDFS-3703
URL: https://issues.apache.org/jira/browse/HDFS-3703
Project: Hadoop HDFS
Issue Type: Improvement
Components: data-node, name-node
Affects Versions: 2.0.0-alpha, 1.0.3
Reporter: nkeywal
By default, if a box dies, the datanode will be marked as dead by the namenode
after 10:30 minutes. In the meantime, this datanode will still be proposed by
the nanenode to write blocks or to read replicas. It happens as well if the
datanode crashes: there is no shutdown hooks to tell the nanemode we're not
there anymore.
It especially an issue with HBase. HBase regionserver timeout for production is
often 30s. So with these configs, when a box dies HBase starts to recover after
30s and, while 10 minutes, the namenode will consider the blocks on the same
box as available. Beyond the write errors, this will trigger a lot of missed
reads:
- during the recovery, HBase needs to read the blocks used on the dead box (the
ones in the 'HBase Write-Ahead-Log')
- after the recovery, reading these data blocks (the 'HBase region') will fail
33% of the time with the default number of replica, slowering the data access,
especially when the errors are socket timeout (i.e. around 60s most of the
time).
Globally, it would be ideal if HDFS settings could be under HBase settings.
As a side note, HBase relies on ZooKeeper to detect regionservers issues.
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