1. Control-based Quality Adaptation in Data Stream Management Systems (DSMS)

2. Data Stream Management System (DSMS)
Continuous data, discarded after being processed
Continuously answers queries
Applications
Financial analysis
Mobile services
Sensor networks
Network monitoring
More …

3. DSMS architecture Network of query operators (1 – 12)
Each operator has its own queue
Scheduler decides which operator to execute
Query results pushed to clients
For our purposes, DSMS can be viewed as a blackbox

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

5. What’s missing? Current solutions focus on steady-state performance
Open-loop control ?
Assuming there inputs reach steady states
However, arrivals are bursty in practice – always in transient state
The solution: closed-loop control

6. Why Closed-Loop Control
Reduce the effects of modeling error, input and output disturbances
Improve dynamic response
Stabilize unstable systems

7. Identification of Database System

8. Control of Database System
Output is delay time
Incoming flow rate fluctuates and unknown
Uncertainties in cost factor

9. Experiments Implemented a controller in a real DSMS – Borealis
With bursty synthetic and real data