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A mutant query plan (MQP) is an XML serialization of a query plan graph, consisting of regular query operators, plus verbatim pieces of XML data and references to resources. A mutant query plan can reference a resource using an abstract, location independent resource name (URN), or a concrete resource location (URL). Every mutant query plan is tagged with a target, the network address of the client interested in the query results. We can use mutant query plans to represent a distributed query at every stage of its processing: from regular query plans, containing just query operators and resource references, to query results, containing just data, and everything in between. When a server receives an MQP it partially evaluates as much of the plan as it can (or is willing to), producing a new, mutated, plan and routes it to some other server that can continue processing. The server that eventually evaluates the whole query routes it back to the target. Server can mutate a plan in two ways: resolution, and reduction. In resolution, the server resolves a URN into a URL, or a URL to its data. In reduction, the server evaluates a subplan of the query, and inserts the results in its place.We believe that MQPs offer a more viable solution for large, heterogeneous, and autonomous distributed systems, than the traditional, coordinator-based approach.Since mutant query plans are alternatively optimized and executed on one server at a time, we lose the benefits of pipelined execution, but gain in flexibility and autonomy. Mutant query plans allow each server to optimize the parts of a query it will run independently, and minimize coordination overhead.
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| Papers and presentations |
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For more information on mutant query plans:
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| A mutant query plan |
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| Resolution |
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| Reduction |