1. Quality-Of-Service (QoS) Panel Mitch Cherniack Brandeis David Maier OGI Rajeev Motwani Stanford Johannes GehrkeCornell Hari BalakrishnanMIT SWiM, Stanford University, January 9, 2003 Scheduled according to their QoS emails…

2. Three Talking Points 1)Why (If) QoS is Appropriate for Streams 2)Expressing QoS for Streams 3)Processing QoS for Streams

3. What is QoS? Resource mgmt driven by  application reqts Each app specifies its own error-tolerance (delay, inaccuracy,…) x U (x) x-axis: Delay (sec), Inaccuracy (% dropped),… y-axis Utility ([0..1]) Utility Functions

4. What is QoS? QoS Specs Used to Drive: Prominent Domain: Networks w/ Real-Time Apps (e.g., multimedia streams) Admission control Resource reservation Load shedding… Resource Management (Bandwidth) Non-Uniform Error-Tolerance (Frame rate, jitter,…)

5. Why QoS is Appropriate for Streams An Example: Battlefield Monitoring Resource Management: numerous data sources (soldiers outfitted with sensors: GPS, vital signs, …) numerous monitoring queries Non-Uniform Error-Tolerance: remote triage (low latency, some inaccuracy ok) remote enemy tracking (some latency ok, accurate) missile detection (low latency, no inaccuracy)

6. Why QoS is Appropriate for Streams Processing QoS Specs for Streams Operator Scheduling Load Shedding Query Optimization Tuple Reordering Load Balancing…

7. QoS-Driven Scheduling Goal: Maximize Overall QoS Choice 1: A: Cost: 1 sec (…, age: 1 sec) B: Cost: 2 sec (…, age: 3 sec) Delay = 2 sec Utility = 0.5 Delay = 5 sec Utility = 0.8 Schedule Box A now rather than later Ideal: Maximize Overall Utility Choice 2:

8. Stream Networks  Packet Networks 1. In-Flight Generation of Tuples 2. Semantic Richness of Tuples Complications in expression of QoS Specs Opportunities in processing QoS Specs

9. Expressing QoS for Streams Packet Networks p p p p p p p p packet lost from result Reasonable measure of inaccuracy: Packets dropped / Total Packets

10. Expressing QoS for Streams Stream Networks pp t Depends on p(t) true  tuple lost from result false  tuple not lost from result tuple lost from result?

11. Expressing QoS for Streams Stream Networks CNT t No, but less accuracy in calculation tuple lost from result?

12. Expressing QoS for Streams Stream Networks t 0 or more tuples lost from result tuple lost from result?

13. Stream Networks  Packet Networks 1. Tuples Generated In-Flight Complications in expression of QoS Specs Multiple Flavors of Inaccuracy (lost tuples, imprecise tuples) Impact of dropped tuples hard to determine (depends on where in network dropped)

14. Stream Networks  Packet Networks 2. Semantic Richness of Tuples Opportunities in processing QoS Specs Aurora example: Value-based QoS Load Shedding: Drop less valuable tuples Scheduling: Process most valuable tuples 1st

15. Conclusions 1)QoS is Appropriate for Streams In-flight tuple generation Complicate Expression/Calculation of QoS Semantic Richness of Tuples Offer Processing Opportunities (Value-Based QoS) Resource management Apps w/ non-uniform toleration of error 2) Streams vs Packets Networks.