[jira] Commented: (LUCENE-1799) Unicode compression

["Robert Muir (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-1799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12779442#action_12779442 ] 

Robert Muir commented on LUCENE-1799:
-------------------------------------

Earwin, if implemented as a directory, we lose many of the advantages.

For example, if you are using BOCU-1, lets say with Hindi language, then according to the stats here: http://unicode.org/notes/tn6/#Performance
* you can encode/decode BOCU-1 to/from UTF-16 more than twice as fast as you can UTF-8 to/from UTF-16 (for this language)
* also, resulting bytes are less than half the size of UTF-8 (for this language), yet sort order is still preserved, so it should work for term dictionary, etc.

Note: I have never measured bocu performance in practice.

I took a look at the flex indexing branch and this appears like this might be possible in the future thru a codec... 


> Unicode compression
> -------------------
>
>                 Key: LUCENE-1799
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1799
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: Store
>    Affects Versions: 2.4.1
>            Reporter: DM Smith
>            Priority: Minor
>
> In lucene-1793, there is the off-topic suggestion to provide compression of Unicode data. The motivation was a custom encoding in a Russian analyzer. The original supposition was that it provided a more compact index.
> This led to the comment that a different or compressed encoding would be a generally useful feature. 
> BOCU-1 was suggested as a possibility. This is a patented algorithm by IBM with an implementation in ICU. If Lucene provide it's own implementation a freely avIlable, royalty-free license would need to be obtained.
> SCSU is another Unicode compression algorithm that could be used. 
> An advantage of these methods is that they work on the whole of Unicode. If that is not needed an encoding such as iso8859-1 (or whatever covers the input) could be used.    

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