Chapter 12 : Panta Rhei ; Flexible Execution Engine for Search Computing Queries

Abstract

The efficient execution of data-intensive computations over services is a challenging task: data are retrieved from remote sources and therefore are not available in the query engine until after the execution of these calls, but the system must be inherently efficient thereafter, by guaranteeing that data is immediately cached and processed efficiently, according to the best query plan. In this chapter, we present a flexible execution model for search computing queries, named Panta Rhei. The proposed execution engine paradigm adopts the producer/consumer model and supports both data-driven and event-driven synchronization, and their interplay. Query plans are modeled as directed graphs, whose nodes are processing units and whose edges are either control or data flows. While control flows synchronize service calls and unit execution, data flows transfer data between units that process data flows to produce query results. We present the specification of Panta Rhei by formally defining the units for data production, consumption, manipulation, and caching, as well as the control and data flows. Finally, we discuss how a query plan is expressed in terms of a query execution plan.