1. Misconceptions About Real-Time Databases IEEE Computer Authors: John Stankovic, Sang Hyuk Son, Jorgen Hansson Presented By: Patti Kraker

2. Definitions • Real-time database is a database system • Queries • Schemas • Transactions • Concurrency control support • Storage management

3. Definitions • Timing constraints associated with transactions • Not every transaction, but some • Data valid for specific time intervals

4. Definitions • Time semantics on data • E.g. sensor data, stock market prices • Semantics indicate valid for certain time period • In a real-time database • Validity interval part of database schema

5. Definitions • Transaction Correctness • Absolute time consistency • Individual data is temporally valid to acceptable degree of accuracy • Relative time consistency • Multiple data items updated within specified time interval of each other • E.g. time and pressure

6. Misconceptions • Real-time systems synonymous with speed • Current database technology can be used in real-time database systems

7. Misconceptions/Research • Real-time database properties: temporality, predictability, specialization • Research areas for real-time databases

8. Real-time systems synonymous with speed

9. Hardware advances • Hardware advances will address real-time database requirements • Parallel processing • Does not mean meet timing constraints • Inc. size and complexity • Hardware alone not ensure data accurate

10. Hardware advances • Sum up hardware advances • Transaction that uses obsolete data more quickly is still incorrect

11. Advanced DB technology • Advancing Standard Protocols • Better buffering, faster commit protocols, better query processing • Can not guarantee deadlines or valid data • Required advances include: • time cognizant protocols, commit processing • transaction scheduling, logging, recovery

12. Advanced DB technology • Sum up advanced db technology • These protocols better at supporting real-time transaction and data correctness than standard database protocols that simply go fast.

13. Real-time = Fast • Fast computing: Aim to minimize response time of transactions • Real-time computing: Aim to meet timing constraints and data validity of transactions and keep database current • Need time cognizant protocols

15. Current DB technology can solve real-time problems

16. Traditional databases • Traditional databases can handle real-time • Can define field that contains validity interval • Every transaction must check this field to ensure absolute and relative validity • Can run earliest deadline scheduling through priority of transaction

17. Traditional databases • By adding those features, moving toward real-time db • More efficient to build them into system than force fit traditional db

18. Db in main memory • Placing a conventional database in main memory is sufficient (non-real-time db designers) • Does eliminate disk delays • Still unpredictable: • Delays due to blocking on locks • Transaction scheduling • Stolen processing time to handle external interrupts

19. Db in main memory • Sum up current db technology • Increases in performance can not completely make up for lack of time-cognizant protocols

20. Real-time DB in main memory • A real-time db must reside totally in main memory (real-time db designers) • Reasons: to increase speed, avoid seek and rotational delays of disks • Primary issue I/O • Minimize response time, maximize throughput, maintain fairness • Typical disk scheduling algorithms are First-Come-First-Served (FCFS), Shortest-Seek-Time-First (SSTF), etc.

21. Real-time DB in main memory • Sum up real-time db in main memory • Since deadline and importance of transaction are not considered when disk request are scheduled, timeliness of transaction is jeopardized.

22. Start of real-time databases • Real-time databases emerged from: • Telecommunications, manufacturing, and avionics applications • Conventional databases not adequate

23. Research of real-time db • Increased audio and video applications • More research problems being addressed