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https://issues.apache.org/jira/browse/HADOOP-6834?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12881352#action_12881352
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Hong Tang commented on HADOOP-6834:
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In the first append, lastLen is 0, lastKey refers to a valid byte array whose
bytes are all zero. So the behavior is determined. However, I do agree that it
is possible for a customary comparator, an zero-length byte array may not be a
legal key type. So it would be nice to do a first-key check.
Ahad, would you be interested in providing a patch, or perhaps share with us a
sample program with customized comparator that fails TFile.Writer.append?
> TFile.append compares initial key against null lastKey
> --------------------------------------------------------
>
> Key: HADOOP-6834
> URL: https://issues.apache.org/jira/browse/HADOOP-6834
> Project: Hadoop Common
> Issue Type: Bug
> Components: io
> Affects Versions: 0.20.1, 0.20.2
> 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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