Add javadoc notes about ICUCollationKeyFilter's speed advantage over 
CollationKeyFilter
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                 Key: LUCENE-1719
                 URL: https://issues.apache.org/jira/browse/LUCENE-1719
             Project: Lucene - Java
          Issue Type: Improvement
          Components: contrib/*
    Affects Versions: 2.4.1
            Reporter: Steven Rowe
            Priority: Trivial
             Fix For: 2.9


contrib/collation's ICUCollationKeyFilter, which uses ICU4J collation, is 
faster than CollationKeyFilter, the JVM-provided java.text.Collator 
implementation in the same package.  The javadocs of these classes should be 
modified to add a note to this effect.

My curiosity was piqued by [Robert Muir's 
comment|https://issues.apache.org/jira/browse/LUCENE-1581?focusedCommentId=12720300#action_12720300]
 on LUCENE-1581, in which he states that ICUCollationKeyFilter is up to 30x 
faster than CollationKeyFilter.

I timed the operation of these two classes, with Sun JVM versions 1.4.2/32-bit, 
1.5.0/32- and 64-bit, and 1.6.0/64-bit, using 90k word lists of 4 languages 
(taken from the corresponding Debian wordlist packages and truncated to the 
first 90k words after a fixed random shuffling), using Collators at the default 
strength, on a Windows Vista 64-bit machine.  I used an analysis pipeline 
consisting of WhitespaceTokenizer chained to the collation key filter, so to 
isolate the time taken by the collation key filters, I also timed 
WhitespaceTokenizer operating alone for each combination, and then subtracted 
it from both of the collation key analysis chains' times.  The rightmost column 
represents the performance advantage of the ICU4J implemtation (ICU) over the 
java.text.Collator implementation (JVM), after discounting the 
WhitespaceTokenizer time (WST): (ICU-WST) / (JVM-WST). The best times out of 5 
runs for each combination, in milliseconds, are as follows:

||Sun JVM||Language||java.text||ICU4J||WhitespaceTokenizer||ICU4J Improvement||
|1.4.2_17 (32 bit)|English|522|212|13|2.6x|
|1.4.2_17 (32 bit)|French|716|243|14|3.1x|
|1.4.2_17 (32 bit)|German|669|264|16|2.6x|
|1.4.2_17 (32 bit)|Ukranian|931|474|25|2.0x|
|1.5.0_15 (32 bit)|English|604|176|16|3.7x|
|1.5.0_15 (32 bit)|French|817|209|17|4.2x|
|1.5.0_15 (32 bit)|German|799|225|20|3.8x|
|1.5.0_15 (32 bit)|Ukranian|1029|436|26|2.4x|
|1.5.0_15 (64 bit)|English|431|89|10|5.3x|
|1.5.0_15 (64 bit)|French|562|112|11|5.5x|
|1.5.0_15 (64 bit)|German|567|116|13|5.4x|
|1.5.0_15 (64 bit)|Ukranian|734|281|21|2.7x|
|1.6.0_13 (64 bit)|English|162|81|9|2.1x|
|1.6.0_13 (64 bit)|French|192|92|10|2.2x|
|1.6.0_13 (64 bit)|German|204|99|14|2.2x|
|1.6.0_13 (64 bit)|Ukranian|273|202|21|1.4x|


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