Characteristics of real-time database system

What are the characteristics of real-time database system? List the characteristics that define real-time database system clearly, Define the characteristics that differentiate real-time database from conventional database

Characteristics of Real-time databases

• Data 
• Temporal data – Type of data whose validity is lost after a specified time. 
• Dynamic data – data from sensors, archival data, input data to actuators etc. 
• Static data – as in conventional system

• Data with time semantics 
• Data have explicit validity intervals

• Timing constraints 
• Response requirements from external world, data are valid for specific time intervals, timing constraints can be on start timings, deadlines or periodic starting etc.

• Real-time database has to maintain logical consistency and temporal consistency of the data.

• Predictable response time 
• If a real-time database transaction misses its deadline it would cause serious implications. Hence to avoid it the response time should be predictable in most of the cases.

• Real-time transactions 
• Transactions with ACID properties supported. 
• In few cases 
• atomicity can be relaxed, 
• isolation may not be needed always, 
• serializability can be relaxed, and 
• not all data are durable.

• Correctness of the data 
• Integrity of the data is required. In few cases correctness can be traded for timeliness.

• Efficient access to the data

• Performance metric 
• Real-time database is evaluated based on calculating the number of transactions missing their deadlines.

• Priority scheduling 
• Transaction processing in a real-time database should be based on priority and criticalness of transactions.

An effective real-time database system needs to be able to handle time-sensitive queries, return only temporally valid data, and support priority scheduling.

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Misconceptions about real time databases

Misconceptions about real-time databases, What cannot be considered as the real-time databases? Some false information that would lead people to have a wrong understanding on what is real-time database.

Misconceptions about real-time databases

Real-time database is sometimes understood mistakenly by many people as follows; actually real-time does not mean fast, or main memory etc.

• Advancement in the hardware technologies will address the requirements of real-time database 
• The improvement in hardware technologies alone cannot make a difference. Hardware improvement has nothing to do with timing constraints of real-time transactions.

• Advancement in database technology can address all the real-time database requirements 
• Improved buffering mechanism, faster commit protocols and state-of-the-art query processing techniques cannot guarantee the deadlines to be met by a transaction or temporal validity of data in a real time database.

• Real-time computing is fast computing 
• Real-time databases aim to meet the timing constraints and data-validity requirements of individual transactions and also keep the database current via proper update rates. This just cannot be achieved with fast computing property.

• All the real-time database requirements can be handled by traditional databases 
• Traditional databases cannot be as efficient as the one real-time database built from scratch for the real-time applications.

• Placing the conventional database in main memory is equivalent to real-time database 
• Placing database in main memory cannot solve this real-time issue. Conventional databases still have many additional sources of unpredictability such as delays due to blocking on locks, transaction scheduling, stolen processing time to handle external interrupts, and so on.

• A real-time database is one which resides totally in main memory only 
• Need not be. Placing the real-time database in main memory will definitely increase the speed of the system. But, we may need to deal with some non-critical disk-resident data as well.

• A temporal database is a real-time database 
• Temporal database deals with the time associated with information whereas real-time database deals with satisfaction of timing constraints with respect to operational aspects. Temporal database may store time based durable data, but real-time database stores time based data with timing constraints like when the data is valid.

• Real-time database cannot achieve predictability 
• This may not be completely true, because in cases like specialized real-time transactions (for example, updating periodic sensor data) or fixed real-time transactions (for example, using the same type of data or amount of data each time) they are predictable.

 

Reference: John A. Stankovic, Sang Hyuk Son, Jorgen Hansson, “Misconceptions about Real-Time Databases,” IEEE Computer, 2009

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Characteristics of real time systems

Characteristics of a real-time system, List the characteristics of a real-time system, What are the important characteristics of a real-time system, List the factors that define a real-time system

Characteristics of Real-time systems

• Timeliness and predictability 
• A system should perform correct operations within the specified time.

• Typically embedded in a large complex system 
• A system which is embedded in a larger system to monitor and control the larger system.

• Dependability (reliability) and fault tolerance 
• Reliability is about how often a system may fail. In other words, how efficiently a system can work over a period of time. 
• Fault tolerance is about the ability to recognize and handle failures.

• Concurrency 
• A system that is capable of handling the input from the environment simultaneously.

• Explicit timing constraints (soft, firm, and hard) 
• A soft system is a system that meets its deadline but may not within time. 
• A hard system has to meet its deadline within the specified time. 
• A firm system has to meet its deadline within the time specified failing which the result may not be accepted.

• Failure will normally involve cost 
• Cost would mean the financial cost or impact on human or other lives.

• Testing of a real-time system 
• Mostly a real-time system can be tested with simulations because of the cost involved in testing with actual environments.

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Types of real time databases

Types of real time databases - What are the types of real-time databases? - Various types of real time databases with respect to transaction deadline - Hard real-time database - Soft real-time database

Types of Real-Time Databases (with respect to transaction deadline)

The type of a real-time database is determined by its transaction characteristics. Especially the deadline of a transaction determines the type. Based on the transaction deadline or when a transaction has to meet its deadline, we can categorize the real-time databases as follows;

• Hard real-time database

• Soft real-time database

 

Hard real-time database

A real-time database with a hard deadline on its transaction is called as hard real-time database. Hard deadline transactions have few or all of the following characteristics;

• Timely and logically correct execution is considered to be critical.

• Missing hard deadline cannot be accepted, because, that lead to catastrophic consequences (serious implications on lives or big financial damage).

• Also called as safety critical deadlines

Hard Deadline

Example:

All safety critical systems are in this category – anti-missile system, patient monitoring system etc.

Soft real-time database

A real-time database with soft deadline transactions is called as soft real-time database. Soft deadline transactions have few or all of the following characteristics;

• Desirable but not critical deadlines

• Missing a deadline will not cause a failure or failure of system’s integrity.

• Result quality degrades after deadline, and may affect quality of service of the system.

Soft Deadline

Example:

Banking system, reservation systems, etc.

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