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Posted to common-dev@hadoop.apache.org by "Michel Tourn (JIRA)" <ji...@apache.org> on 2006/05/16 22:51:06 UTC

[jira] Updated: (HADOOP-136) Overlong UTF8's not handled well

     [ http://issues.apache.org/jira/browse/HADOOP-136?page=all ]

Michel Tourn updated HADOOP-136:
--------------------------------

    Attachment: largeutf8.patch

Here is the patch, two new files:

org.apache.hadoop.io.TestLargeUTF8
org.apache.hadoop.io.LargeUTF8

The only difference with the UTF8 string format is that 
the length is stored on 4 bytes rather than 2 bytes.

TestLargeUTF8 tests serialization of larger strings up to 1MB




> Overlong UTF8's not handled well
> --------------------------------
>
>          Key: HADOOP-136
>          URL: http://issues.apache.org/jira/browse/HADOOP-136
>      Project: Hadoop
>         Type: Bug

>   Components: io
>     Reporter: Dick King
>     Priority: Minor
>  Attachments: largeutf8.patch
>
> When we feed an overlong string to the UTF8 constructor, two suboptimal things happen.
> First, we truncate to 0xffff/3 characters on the assumption that every character takes three bytes in UTF8.  This can truncate strings that don't need it, and it can be overoptimistic since there are characters that render as four bytes in UTF8.
> Second, the code doesn't actually handle four-byte characters.
> Third, there's a behavioral discontinuity.  If the string is "discovered" to be overlong by the arbitrary limit described above, we truncate with a log message, otherwise we signal a RuntimeException.  One feels that both forms of truncation should be treated alike.  However, this issue is concealed by the second issue; the exception will never be thrown because UTF8.utf8Length can't return more than three times the length of its input.
> I would recommend changing UTF8.utf8Length to let its caller know how many characters of the input string will actually fit if there's an overflow [perhaps by returning the negative of that number] and doing the truncation accurately as needed.
> -dk

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