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From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] Created: (DERBY-2699) performance of like in territory based collation databases may be improved by changing way collation elements are calculated.
Date Sat, 26 May 2007 00:22:17 GMT
performance of like in territory based collation databases may be improved by changing way
collation elements are calculated.
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                 Key: DERBY-2699
                 URL: https://issues.apache.org/jira/browse/DERBY-2699
             Project: Derby
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 10.3.0.0
            Reporter: Mike Matrigali


WorkHorseForCollatorDatatypes.java has a method getCollationElementsForString() which currently
gets
called when processing like clauses in databases that have been created with territory based
collation, this is
not an issue in pre-10.3 databases or post 10.3 default databases.
getCollationElementsForString gets the collation elements for the entire  value of the String
held by
the datatype using the class.

If you take the case of pattern 'A%' and the value of datatype is 'BXXXXXXXXXXXXXXXXXXXXXXX',

then it would have been better to  better to get collation elements one character of the String
value at a time
to avoid the  process of getting collation elements for the entire string when we don't really
need it 
One could imagine this might have a huge performance impact on running like against a long
clob where
the like pattern has leading fixed-length pattern to match.

Comments on this from Dan and Dag can be found in DERBY-2416.

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