Misconceptions About Real-Time Databases

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Misconceptions About Real-Time Databases

• IEEE Computer
• Authors John Stankovic, Sang Hyuk Son, Jorgen
  Hansson
• Presented By Patti Kraker

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Definitions

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

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Definitions

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

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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

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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

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Misconceptions

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

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Misconceptions/Research

• Real-time database properties temporality,
  predictability, specialization
• Research areas for real-time databases

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Real-time systems synonymous with speed
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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

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Hardware advances

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

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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

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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.

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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

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Current DB technology can solve real-time problems
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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

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Traditional databases

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

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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

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Db in main memory

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

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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.

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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.

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Start of real-time databases

• Real-time databases emerged from
• Telecommunications, manufacturing, and avionics
  applications
• Conventional databases not adequate

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Research of real-time db

• Increased audio and video applications
• More research problems being addressed