misconceptions about real- time databases ieee computer authors: john stankovic, sang hyuk son,...
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Definitions Timing constraints associated with transactions Not every transaction, but some Data valid for specific time intervalsTRANSCRIPT
Misconceptions About Real-Time Databases
IEEE Computer Authors: John Stankovic, Sang Hyuk
Son, Jorgen HanssonPresented 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