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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