1. Control-based Quality Adaptation in Data Stream Management Systems (DSMS) Yicheng Tu†, Song Liu‡, Sunil Prabhakar†, and Bin Yao‡ † Department of Computer Sciences, Purdue University, USA ‡ School of Mechanical Engineering, Purdue University, USA

2. Data Stream Management Continuous data, discarded after being processed Continuous query Data-active query- passive model Applications –Financial analysis –Mobile services –Sensor networks –Network monitoring –More …

3. DSMS architecture Network of query operators (O1 – O3) Each operator has its own queue (q1 – q4) Scheduler decides which operator to execute Query results (Q1, Q2) pushed to clients Example systems: –Aurora/Borealis –STREAM

4. Quality-of-Service (QoS) in DSM Data processing is QoS-critical in DSMS –Tuple delay is the major concern: results generated from old data are useless! Highly dynamic environment  hard to maintain QoS –Bursty data input –Unpredictable unit processing cost Overloading during spikes  degraded (delay) QoS Solution: adjust data loss  load shedding

5. Load Shedding Eliminating excessive load by dropping data items  less QoS violations Key questions –When? –How much? –Where? –Which tuples? Basic algorithm (Tatbul et al., 2003): periodically

6. What’s wrong? Fail to capture current system status (queue length) and output (delay) –Delay positively related to queue length Examples 1. Unbounded increase of delay Example 2. Unnecessary data loss

7. Our approach View load shedding as a feedback control problem Feedback Control: manipulation of system behavior by adjusting system input based on system output –Cruise control of automobiles, room temperature control, etc. The feedback control loop: –Plant –Monitor –Controller –Actuator How it works –Error = measured output – desirable output –Focal point: controller, which maps error to control signal

8. Why Feedback Control ?

9. The feedback control loop Plant : current DSMS –Input : load admitted –Output : delay QoS –Reference output: specified by DBA Actuator –adaptor: load shedder –admission controller Monitor : new Controller : new System dynamics: disturbances Discrete control: control period T

10. Controller design Performed all three steps in a real DSMS – the Borealis system We set output to average delay System identification gives a first-order model structure Control function Controller analysis gives the following set of parameters:

11. Experiments

12. Experimental results

16. Summary Load shedding is an important quality adaptation method Current solutions focusing on steady-state performance do not work well under bursty inputs We propose an approach to guide load shedding in a highly dynamic environment based on feedback control theory Initial experimental results show promising potential of our approach