Package org.eclipse.rdf4j.repository.sail

Class SailQuery

    • Method Detail

      • explain

        public Explanation explain​(Explanation.Level level)
        Description copied from interface: Query

        Explain how the query will be (or has been) executed/evaluated by returning an explanation of the query plan.

        This method is useful for understanding why a particular query is slow. The most useful level is Executed, but this takes as long as it takes to execute/evaluate the query.

        When timing a query you should keep in mind that the query performance will vary based on how much the JIT compiler has compiled the code (C1 vs C2) and based on what is or isn't cached in memory. If Timed explanations are considerably slower than Executed explanations the overhead with timing the query may be large on your system and should not be trusted.

        WARNING: This method is experimental and is subject to change or removal without warning. Same goes for the returned explanation. There is currently only partial support for this method in RDF4J and and UnsupportedOperationException where support is lacking.

        Parameters:
        level - The explanation level that should be used to create the explanation. Choose between: Unoptimized (as parsed without optimizations) , Optimized (as is actually going to be used), Executed (as was executed/evaluated, including some real performance metrics), Timed (as was executed/evaluated including all real performance metrics). Executed and Timed level can potentially be slow.
        Returns:
        The explanation that we generated, which can be viewed in a human readable format with toString(), as JSON or as a simplified query plan object structure.