When I work on
HDFS-624, I saw TestFileAppend3#TC7 occasionally fails. After lots of debug, I saw that the client unexpected received a response of "-2 SUCCESS SUCCESS" in which -2 is the packet sequence number. This happened in a pipeline of 2 datanodes and one of them failed. It turned out when block receiver fails, it shuts down itself and interrupts the packet responder but responder tries to handle interruption with the condition "Thread.isInterrupted()" but unfortunately a thread's interrupt status is not set in some cases as explained in the Thread#interrupt javadoc:
If this thread is blocked in an invocation of the wait(), wait(long), or wait(long, int) methods of the Object class, or of the join(), join(long), join(long, int), sleep(long), or sleep(long, int), methods of this class, then its interrupt status will be cleared and it will receive an InterruptedException.
So datanode does not detect the interruption and continues as if no error occurs.