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https://issues.apache.org/jira/browse/DERBY-2698?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13542885#comment-13542885
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Knut Anders Hatlen commented on DERBY-2698:
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After DERBY-3136 and DERBY-2699 we no longer calculate the array of ints.
There may still be some potential for caching. For example, a query such as
SELECT * FROM t WHERE x LIKE pattern ESCAPE '#'
will call WorkHorseForCollatorDatatypes.hasSingleCollationElement() on the
escape string '#' once for each row in the table T, and each call will allocate
a CollationElementIterator and redo the check.
But it's more of a corner case now than when the issue was filed, so maybe we
can just close it as Won't Fix.
> caching collation elements in WorkHorseForCollatorDatatypes may improve
> performance.
> ------------------------------------------------------------------------------------
>
> Key: DERBY-2698
> URL: https://issues.apache.org/jira/browse/DERBY-2698
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 10.3.1.4
> Reporter: Mike Matrigali
> Priority: Minor
> Labels: derby_triage10_10
>
> In
> java/engine/org/apache/derby/iapi/types/WorkHorseForCollatorDatatypes.getCollationElementsForString()
> an array
> of int's is calculated given the string and the collator in place. If like
> is ever called on the same DataValueDescriptor, caching
> this calculation will be faster than redoing the calculation. To make this
> change one needs to properly invalidate the cached
> information when the base type value is changed. For instance in the case of
> SQLChar() the following routines all result
> in a change in the value of the datatype and thus need to invalidate any
> cached collation element structure:
> readExternalFromArray()
> readExternal()
> setValue()
> there may be others.
> DERBY-2670 is an example of what can go wrong if you get the caching wrong.
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