translation alternatives • Runtime optimizations • load management, scheduling, state management • Optimization semantics, correctness, profitability Topics covered in this lecture ??? Vasiliki Kalavri | different strategies? • before execution or during runtime Query optimization (I) ??? Vasiliki Kalavri | Boston University 2020 10 Optimization strategies • enumerate equivalent execution plans • minimize minimize monetary costs (if running in the cloud) Query optimization (II) ??? Vasiliki Kalavri | Boston University 2020 Cost-based optimization 11 Parsed program representation Optimizer statistics

seddon_2011_07_28.png 5 ??? Vasiliki Kalavri | Boston University 2020 Load shedding as an optimization problem N: query network I: set of input streams with known arrival rates C: system processing probability to discard a tuple and is computed based on statistics and operator selectivity • The optimization objective is to achieve the highest possible accuracy given the constraint that system throughput