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

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

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

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

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

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

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

Real-time systems synonymous with speed

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

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

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

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.

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

Current DB technology can solve real-time problems

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

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

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

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

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.

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.

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

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