Challenges of reconfiguration ??? Vasiliki Kalavri | Boston University 2020 12 • Detect environment changes: external workload and system performance • Identify bottleneck operators, straggler workers Kalavri | Boston University 2020 Control: When and how much to adapt? 12 • Detect environment changes: external workload and system performance • Identify bottleneck operators, straggler workers and how much to adapt? Mechanism: How to apply the re-configuration? 12 • Detect environment changes: external workload and system performance • Identify bottleneck operators, straggler workers

When and how much to adapt? Mechanism: How to apply the re-configuration? 3 • Detect environment changes: external workload and system performance • Identify bottleneck operators, straggler workers utilization > 70% => scale out • Analytical dataflow-based models Action • Speculative: small changes at one operator at a time • Predictive: at-once for all operators 8 ??? Vasiliki Kalavri | Boston

Vasiliki Kalavri | Boston University 2020 15 The standard error of the LogLog algorithm is inversely related to the number of counters m: Standard error δ ≈ 1.3 m For m = 256, the error is about University 2020 27 For a standard error of , we need at least hash functions. δ ≈ 1 % p = ⌈ln 1 δ ⌉ = 5 Space requirements ??? Vasiliki Kalavri | Boston University 2020 27 For a standard error of , we need ϵ = 10 107 = 10−6 Space requirements ??? Vasiliki Kalavri | Boston University 2020 27 For a standard error of , we need at least hash functions. δ ≈ 1 % p = ⌈ln 1 δ ⌉ = 5 Consider a stream of

• DB query results depend on a snapshot and clients are not notified if their query result changes later. 13 Message delivery and ordering Acknowledgements are messages from the client to the broker

your dashboards and alerts over time and, more importantly, observe the performance impact of the changes to your application throughout the development phase. By doing so, you can ask the right questions

Kalavri | Boston University 2020 Three classes of operators: • relation-to-relation: similar to standard SQL and define queries over tables. • stream-to-relation: define tables by selecting portions subset of SQL that excludes non- monotonic constructs: • EXCEPT, NOT EXIST, NOT IN and ALL • all standard blocking aggregates Can we express all streaming (monotonic queries) with NB-SQL? 30 Vasiliki