[
https://issues.apache.org/jira/browse/HADOOP-1489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12504553
]
dhruba borthakur commented on HADOOP-1489:
------------------------------------------
Does this problem exist in previous release, e.g. 0.12.3? It will be good to
know whether this was introduced in 0.13 release. Thanks.
> 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
> Attachments: MRIdentity.java, slashr33.txt
>
>
> 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
> {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));
> }
> {code}
> 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 (see the callee one starts with
> "Caused by")
> -------------------------------------
> {code}
> 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
> {code}
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
