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https://issues.apache.org/jira/browse/CAY-1667?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13208508#comment-13208508
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Andrus Adamchik commented on CAY-1667:
--------------------------------------
Talking of orderings, since expression is always a property path, do we even
care to do a full parse? We can probably just check whether this is DB or Obj
path, and instantiate an approprate ASTXyzPath.
> Expression parser performance optimization
> ------------------------------------------
>
> Key: CAY-1667
> URL: https://issues.apache.org/jira/browse/CAY-1667
> Project: Cayenne
> Issue Type: Improvement
> Components: Core Library
> Affects Versions: 3.1M3
> Reporter: Andrus Adamchik
> Assignee: Andrus Adamchik
>
> Inspecting some profiling data from a customer I see an inefficiency inside
> Expression.fromString. It was actually discovered inside Ordering class, that
> compiles path string on demand, so it affects even the queries that do not
> use 'fromString', as well Orderings created for in-memory sorting. There are
> 2 culprits in JavaCharStream that is generated by javaCC (although
> JavaCharStream is not a part of the parser, so we can probaby change the code
> on top of the generated class) :
> 1. JavaCharStream.fillBuff() has throw new java.io.IOException(); that is
> caught right in that same method (!!!) Throwable.fillStackTrace() shows as a
> "hot spot" in the profile. There should be a better way to handle if/else
> condition :)
> 2. Expression.fromString -> new ExpressionParser(Reader) -> new
> JavaCharStream(Reader, int startline, int startcolumn)
> JavaCharStream constructor is heavy and shows as a hotspot. For one thing it
> creates 4 int/char buffers with size of 4096 each. I don't think we have such
> long expressions ever, and don't need all this memory. Moreover we can
> probably guess the max needed buffer size from the original String length. My
> guess is that most expressions are under 100-300 chars. Certainly true for
> the orderings.
>
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