Kihwal Lee created HDFS-9178:
--------------------------------
Summary: Slow datanode I/O can cause a wrong node to be marked bad
Key: HDFS-9178
URL: https://issues.apache.org/jira/browse/HDFS-9178
Project: Hadoop HDFS
Issue Type: Bug
Reporter: Kihwal Lee
Priority: Critical
When non-leaf datanode in a pipeline is slow on or stuck at disk I/O, the
downstream node can timeout on reading packet since even the heartbeat packets
will not be relayed down.
The packet read timeout is set in {{DataXceiver#run()}}:
{code}
peer.setReadTimeout(dnConf.socketTimeout);
{code}
When the downstream node times out and closes the connection to the upstream,
the upstream node's {{PacketResponder}} gets {{EOFException}} and it sends an
ack upstream with the downstream node status set to {{ERROR}}. This caused the
client to exclude the downstream node, even thought the upstream node was the
one got stuck.
The connection to downstream has longer timeout, so the downstream will always
timeout first. The downstream timeout is set in {{writeBlock()}}
{code}
int timeoutValue = dnConf.socketTimeout +
(HdfsConstants.READ_TIMEOUT_EXTENSION * targets.length);
int writeTimeout = dnConf.socketWriteTimeout +
(HdfsConstants.WRITE_TIMEOUT_EXTENSION * targets.length);
NetUtils.connect(mirrorSock, mirrorTarget, timeoutValue);
OutputStream unbufMirrorOut = NetUtils.getOutputStream(mirrorSock,
writeTimeout);
{code}
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