[jira] Created: (HADOOP-6834) TFile.append compares initial key against null lastKey

["Ahad Rana (JIRA)" <ji...@apache.org>]

TFile.append compares initial key against null lastKey  
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                 Key: HADOOP-6834
                 URL: https://issues.apache.org/jira/browse/HADOOP-6834
             Project: Hadoop Common
          Issue Type: Bug
          Components: io
    Affects Versions: 0.20.2, 0.20.1
            Reporter: Ahad Rana


The following code in TFile.KeyReigster.close: 


            byte[] lastKey = lastKeyBufferOS.getBuffer();
            int lastLen = lastKeyBufferOS.size();
            if (tfileMeta.getComparator().compare(key, 0, len, lastKey, 0,
                lastLen) < 0) {
              throw new IOException("Keys are not added in sorted order");
            }

compares the initial  key (passed in via  TFile.Writer.append) against a technically NULL lastKey. lastKey is not initialized until after the first call to TFile.Writer.append. The underlying RawComparator interface used for comparisons does not stipulate the proper behavior when either length 1  or length 2 is zero. In the case of LongWritable, its WritableComparator implementation does an unsafe read on the passed in byte arrays b1 and b2. Since TFile pre-allocates the buffer used for storing lastKey, this passes a valid buffer with zero count to LongWritable's comparator, which ignores length and thus produces incorrect results. 


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