He Tianyi created HDFS-10490:
--------------------------------
Summary: Client may never recovery replica after a timeout during
sending packet
Key: HDFS-10490
URL: https://issues.apache.org/jira/browse/HDFS-10490
Project: Hadoop HDFS
Issue Type: Bug
Components: datanode
Affects Versions: 2.6.0
Reporter: He Tianyi
For newly created replica, a meta file is created in constructor of
{{BlockReceiver}} (for {{WRITE_BLOCK}} op). Its header will be written lazily
(buffered in memory first by {{BufferedOutputStream}}).
If following packets fail to deliver (e.g. in extreme network condition), the
header may never get flush until closed.
However, {{BlockReceiver}} will not call close until block receiving is
finished or exception(s) encountered. Also in extreme network condition, both
RST & FIN may not deliver in time.
In this case, if client tries to initiates a {{transferBlock}} to a new
datanode (in {{addDatanode2ExistingPipeline}}), existing datanode will see an
empty meta if its {{BlockReceiver}} did not close in time.
Then, after HDFS-3429, a default {{DataChecksum}} (NULL, 512) will be used
during transfer. So when client then tries to recover pipeline after completely
transferred, it may encounter the following exception:
{noformat}
java.io.IOException: Client requested checksum DataChecksum(type=CRC32C,
chunkSize=4096) when appending to an existing block with different chunk size:
DataChecksum(type=NULL, chunkSize=512)
at
org.apache.hadoop.hdfs.server.datanode.ReplicaInPipeline.createStreams(ReplicaInPipeline.java:230)
at
org.apache.hadoop.hdfs.server.datanode.BlockReceiver.<init>(BlockReceiver.java:226)
at
org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:798)
at
org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(Receiver.java:166)
at
org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:76)
at
org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:243)
at java.lang.Thread.run(Thread.java:745)
{noformat}
This will repeat, until exhausted by datanode replacement policy.
Also to note that, with bad luck (like I), 20k clients are all doing this. It's
to some extend a DDoS attack to NameNode (because of getAdditionalDataNode
calls).
I suggest we flush immediately after header is written, preventing anybody from
seeing empty meta file for avoiding the issue.
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