[jira] [Created] (JENA-1862) Query.cloneQuery is slow

["Claus Stadler (Jira)" <ji...@apache.org>]

Claus Stadler created JENA-1862:
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             Summary: Query.cloneQuery is slow
                 Key: JENA-1862
                 URL: https://issues.apache.org/jira/browse/JENA-1862
             Project: Apache Jena
          Issue Type: Improvement
          Components: ARQ
    Affects Versions: Jena 3.14.0
            Reporter: Claus Stadler


This is a follow up to JENA-1861 which is about the thread safety of Query objects. As sharing a Query object across threads may introduce race condition, the obvious workaround would be to just clone it. However, the current implementation serializes the query to string and then re-parses it which causes a very high overhead (for my use case it became the top entry in the VisualVM profiler).

Proposal:
* Extend ElementTransformCopyBase with a 'alwaysCopy' flag analogous to ExprTransformCopy
* Add a new constructor to ExprTransformApplyElementTransform(ElementTransform transform, boolean alwaysCopy) so that the alwayCopy flag of the underlying ExprTransformCopy can be set to true
* Implement clone using syntatic transforms as below

{code}
public static Query fastClone(Query query) {
    ElementTransform eltXform = new ElementTransformCopyBase2(true);
    ExprTransform exprXform = new ExprTransformApplyElementTransform2(eltXform, true);
    Query result = QueryTransformOps.transform(query, eltXform, exprXform);
    return result;
}
{code}

This approach 'work-for-me' and I can create a pull request for this, but maybe there are more subtleties to the outlined approach that need to be considered?




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