FAQ
BlockMissingException upon concurrent read and write: reader was doing file position read while writer is doing write without hflush
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Key: HDFS-1907
URL: https://issues.apache.org/jira/browse/HDFS-1907
Project: Hadoop HDFS
Issue Type: Bug
Components: hdfs client
Affects Versions: 0.23.0
Environment: Run on a real cluster

$ hadoop version
Hadoop 0.22.0.1105090202
Subversion git://hadoopre5.corp.sk1.yahoo.com/home/y/var/builds/thread2/workspace/Cloud-HadoopCommon-0.22-Secondary -r 3c23e43f9e262e7843e4287436429fad3224b0f7
Compiled by hadoopqa on Mon May 9 02:13:09 PDT 2011
From source with checksum 90b5fc469fd7a1fa0ba22db893423fed
Reporter: CW Chung


BlockMissingException is thrown under this test scenario:
- two different processes doing concurrent file r/w: one read and the other write on the same file
- writer keep doing file write
- reader doing position file read from beginning of the file to the visible end of file, repeatedly

The call is basically:
byteRead = in.read(currentPosition, buffer, 0, byteToReadThisRound);
where CurrentPostion=0, buffer is a byte array buffer, byteToReadThisRound = 1024*10000;
Usually it does not fail right away. I have to read, close file, re-open the same file a few times to create the problem. I'll pose a test program to repro this problem after I've cleaned up a bit my current test program.


Error msg:
=========================
11/05/08 19:05:48 WARN hdfs.DFSClient: Failed to connect to /98.137.98.116:1004 for file /tmp/N/909NF for block
BP-1632719171-98.137.98.114-1303748685682:blk_-8940328094159486414_3653:java.io.IOException: Got error for
OP_READ_BLOCK, self=/98.137.98.125:36405, remote=/98.137.98.116:1004, for file /tmp/N/909NF, for pool
BP-1632719171-98.137.98.114-1303748685682 block -8940328094159486414_3653
at org.apache.hadoop.hdfs.BlockReader.newBlockReader(BlockReader.java:398)
at org.apache.hadoop.hdfs.DFSInputStream.fetchBlockByteRange(DFSInputStream.java:631)
at org.apache.hadoop.hdfs.DFSInputStream.read(DFSInputStream.java:704)
at org.apache.hadoop.fs.FSDataInputStream.read(FSDataInputStream.java:51)
at TAppend.readUntilVisibleEnd(TAppend.java:441)
at TAppend.readUntilEnd(TAppend.java:474)
at TAppend.testReadOnly(TAppend.java:956)
at TAppend.main(TAppend.java:1215)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.util.RunJar.main(RunJar.java:192)
....
##### Caught Exception in testReadOnly while reading.
java.io.IOException: Exception caught in readUntilVisibleEnd: Reader currentOffset = 0 ; totalByteRead =0 ; latest byteRead = 0 ; visibleLen= 67824640 ; byteLeftToRead = 67824640 ; bufferLen = 10240000 ; chunkNumber= 0 ; input pos = 0 ; byteToReadThisRound = 10240000 ; Filename = /tmp/N/909NF, ReadParam - CurrentPostion=0, offset=0, size=10240000


at TAppend.readUntilVisibleEnd(TAppend.java:457)
at TAppend.readUntilEnd(TAppend.java:474)
at TAppend.testReadOnly(TAppend.java:956)
at TAppend.main(TAppend.java:1215)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.util.RunJar.main(RunJar.java:192)

Caused by: org.apache.hadoop.hdfs.BlockMissingException: Could not obtain block:
BP-1632719171-98.137.98.114-1303748685682:blk_-8940328094159486414_3653 file=/tmp/N/909NF
at org.apache.hadoop.hdfs.DFSInputStream.chooseDataNode(DFSInputStream.java:570)
at org.apache.hadoop.hdfs.DFSInputStream.fetchBlockByteRange(DFSInputStream.java:618)
at org.apache.hadoop.hdfs.DFSInputStream.read(DFSInputStream.java:704)
at org.apache.hadoop.fs.FSDataInputStream.read(FSDataInputStream.java:51)
at TAppend.readUntilVisibleEnd(TAppend.java:441)
... 8 more


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