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From "Konstantin Boudnik (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1459) NullPointerException in DataInputStream.readInt
Date Wed, 20 Oct 2010 18:22:26 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1459?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12923075#action_12923075
] 

Konstantin Boudnik commented on HDFS-1459:
------------------------------------------

Thanks for opening new JIRA, Hajo. One thing: in the future, please try to limit 'Description'
field to a self-explanatory short diagnosis of a problem and post any error messages, code
snippets, etc. as 'Comment' messages.

> NullPointerException in DataInputStream.readInt
> -----------------------------------------------
>
>                 Key: HDFS-1459
>                 URL: https://issues.apache.org/jira/browse/HDFS-1459
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 0.20.1
>         Environment: Debian 64 bit
> Cloudera Hadoop
>            Reporter: Hajo Nils Krabbenhöft
>
> First, here's my source code accessing the HDFS:
> final FSDataInputStream indexFile = getFile(bucketPathStr, Integer.toString(hashTableId)
+ ".index");
> indexFile.seek(bucketId * 4);
> int bucketStart = ByteSwapper.swap(indexFile.readInt());
> int bucketEnd = ByteSwapper.swap(indexFile.readInt());
> final FSDataInputStream dataFile = getFile(bucketPathStr, Integer.toString(hashTableId)
+ ".data");
> dataFile.seek(bucketStart * (2 + Hasher.getConfigHashLength()) * 4);
> for (int hash = bucketStart; hash < bucketEnd; hash++) {
> 	int RimageIdA = ByteSwapper.swap(dataFile.readInt());
> 	int RimageIdB = ByteSwapper.swap(dataFile.readInt());
> 	....... read hash of length Hasher.getConfigHashLength() and work with it ....
> }
> As you can see, i am reading the range to be read from an X.index file and then read
these rows from X.data. The index file is always exactly 6.710.888 bytes in length.
> As for the data file, everything works fine with 50 different 1.35 GB (22 blocks) data
files and it fails every time i tried with 50 different 2.42 GB (39 blocks) data files. So
the cause of the bug is clearly dependent on the file size.
> I checked for ulimit and for the number of network connections and they are both not
maxed out when the error occurs. The stack trace i get is:
> java.lang.NullPointerException
> 	at org.apache.hadoop.hdfs.DFSClient$DFSInputStream.readBuffer(DFSClient.java:1703)
> 	at org.apache.hadoop.hdfs.DFSClient$DFSInputStream.read(DFSClient.java:1755)
> 	at org.apache.hadoop.hdfs.DFSClient$DFSInputStream.read(DFSClient.java:1680)
> 	at java.io.DataInputStream.readInt(DataInputStream.java:370)
> ...
> 	at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:50)
> 	at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:358)
> 	at org.apache.hadoop.mapred.MapTask.run(MapTask.java:307)
> 	at org.apache.hadoop.mapred.Child.main(Child.java:170)
> which leads me to believe that DFSClient.blockSeekTo returns with a non-null chosenNode
but with blockReader = null.
> Since the exact same jar works flawlessly with small data files and fails reliably with
big data files, i'm wondering how this could possibly dependent on the file's size or block
count (DFSClient.java line 1628+):
> s = socketFactory.createSocket();
> NetUtils.connect(s, targetAddr, socketTimeout);
> s.setSoTimeout(socketTimeout);
> Block blk = targetBlock.getBlock();
> blockReader = BlockReader.newBlockReader(s, src, blk.getBlockId(), 
>     blk.getGenerationStamp(),
>     offsetIntoBlock, blk.getNumBytes() - offsetIntoBlock,
>     buffersize, verifyChecksum, clientName);
> return chosenNode;

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