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From "Bwolen Yang (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-1489) Input file get truncated for text files with \r\n
Date Wed, 13 Jun 2007 18:24:25 GMT
Input file get truncated for text files with \r\n
-------------------------------------------------

                 Key: HADOOP-1489
                 URL: https://issues.apache.org/jira/browse/HADOOP-1489
             Project: Hadoop
          Issue Type: Bug
          Components: io
    Affects Versions: 0.13.0
            Reporter: Bwolen Yang



When input file has \r\n, LineRecordReader uses mark()/reset() to read one byte ahead to check
if \r is followed by \n.   This probably caused the BufferedInputStream to issue a small read
request (e.g., 127 bytes).   The  ChecksumFileSystem.FSInputChecker.read()
code 
   public int read(byte b[], int off, int len) throws IOException {
     // make sure that it ends at a checksum boundary
     long curPos = getPos();
     long endPos = len+curPos/bytesPerSum*bytesPerSum;
     return readBuffer(b, off, (int)(endPos-curPos));
   }

tries to truncate "len" to checksum boundary.  For DFS, bytesPerSum is 512.  So for small
reads, the truncated length become negative (i.e., endPos - curPos is < 0).   The underlying
DFS read returns 0 when length is negative.  However, readBuffer changes it to -1 assuming
end-of-file has been reached.   This means effectively, the rest of the input file did not
get read.  In my case, only 8MB of a 52MB file is actually read.   Two sample stacks are appended.

One related issue, if there are assumptions (such as len >= bytesPerSum) in FSInputChecker's
read(), would it be ok to add a check that throws an exception when the assumption is violated?
  This assumption is a bit unusal and as code changes (both Hadoop and Java's implementation
of BufferedInputStream), the assumption may get violated.  This silently dropping large part
of input seems really difficult for people to notice (and debug) when people start to deal
with terabytes of data.   Also, I suspect the performance impact for such a check would not
be noticed.

bwolen

Here are two sample stacks.  (i have readbuffer throw when it gets 0 bytes, and have inputchecker
catches the
exception and rethrow both.  This way, I catch the values from both caller and callee.

-------------------------------------

java.lang.RuntimeException: end of read()
in=org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker len=127
pos=45223932 res=-999999
       at org.apache.hadoop.fs.FSDataInputStream$PositionCache.read(FSDataInputStream.java:50)
       at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
       at java.io.BufferedInputStream.read(BufferedInputStream.java:237)
       at org.apache.hadoop.fs.FSDataInputStream$Buffer.read(FSDataInputStream.java:116)
       at java.io.FilterInputStream.read(FilterInputStream.java:66)
       at org.apache.hadoop.mapred.LineRecordReader.readLine(LineRecordReader.java:132)
       at org.apache.hadoop.mapred.LineRecordReader.readLine(LineRecordReader.java:124)
       at org.apache.hadoop.mapred.LineRecordReader.next(LineRecordReader.java:108)
       at org.apache.hadoop.mapred.MapTask$1.next(MapTask.java:168)
       at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:44)
       at org.apache.hadoop.mapred.MapTask.run(MapTask.java:186)
       at org.apache.hadoop.mapred.TaskTracker$Child.main(TaskTracker.java:1720)
Caused by: java.lang.RuntimeException: end of read()
datas=org.apache.hadoop.dfs.DFSClient$DFSDataInputStream pos=45223932
len=-381 bytesPerSum=512 eof=false read=0
       at org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker.readBuffer(ChecksumFileSystem.java:200)
       at org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker.read(ChecksumFileSystem.java:175)
       at org.apache.hadoop.fs.FSDataInputStream$PositionCache.read(FSDataInputStream.java:47)
       ... 11 more
---------------

java.lang.RuntimeException: end of read()  in=org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker
len=400 pos=4503 res=-999999
	at org.apache.hadoop.fs.FSDataInputStream$PositionCache.read(FSDataInputStream.java:50)
	at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
	at java.io.BufferedInputStream.read(BufferedInputStream.java:237)
	at org.apache.hadoop.fs.FSDataInputStream$Buffer.read(FSDataInputStream.java:116)
	at java.io.FilterInputStream.read(FilterInputStream.java:66)
	at org.apache.hadoop.mapred.LineRecordReader.readLine(LineRecordReader.java:132)
	at org.apache.hadoop.mapred.LineRecordReader.readLine(LineRecordReader.java:124)
	at org.apache.hadoop.mapred.LineRecordReader.next(LineRecordReader.java:108)
	at org.apache.hadoop.mapred.MapTask$1.next(MapTask.java:168)
	at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:44)
	at org.apache.hadoop.mapred.MapTask.run(MapTask.java:186)
	at org.apache.hadoop.mapred.TaskTracker$Child.main(TaskTracker.java:1720)
Caused by: java.lang.RuntimeException: end of read()  datas=org.apache.hadoop.dfs.DFSClient$DFSDataInputStream
pos=4503 len=-7 bytesPerSum=512 eof=false read=0
	at org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker.readBuffer(ChecksumFileSystem.java:200)
	at org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker.read(ChecksumFileSystem.java:175)
	at org.apache.hadoop.fs.FSDataInputStream$PositionCache.read(FSDataInputStream.java:47)
	... 11 more



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