Select Page

Real-time vs. Non-real-time Database Systems

Like conventional database systems, real-time database systems are data repositories and provide services for storage, retrieval and manipulation of data. The differences between conventional and real-time database systems lie in the temporal requirements of the managed data, timing constraints on transactions, and performance goals. The following aspects are often considered:

a) internal versus external consistency constraints and,
b) transaction schedules and performance metrics.

The design principles of conventional (i.e., non-real-time) database systems always guarantee strong internal data consistency — a consistent view from all components of the database, avoiding contradictory data in the same database. To guarantee internal consistency, database systems ensure transactions’ ACIDAtomicity, Consistency, Isolation and Durability properties.  Real-time database system designers sometimes argue that, for real-time databases, external consistency (the requirement for a transaction to reflect the current physical environment), is preferable. Indeed, external consistency may be more important than internal consistency for certain applications. However, as a practical matter, most applications require preserving their databases’ internal consistency.

Performance metrics

The common performance metric for all database systems is response time. For conventional database systems, the metric comes down to a number of transactions per time unit; this measurement – the average number of transactions per second (TPS) –  is used heavily in optimizing the responsiveness of traditional database applications. In contrast, real-time database systems often use firm deadline semantics for transactions — transactions can “meet” (successfully commit) or “miss” (successfully abort) their deadlines, but cannot be “late” (go over their allotted time slot) to commit or abort their execution. A late commit of a real-time transaction can lead to a system’s state being incoherent. Thus, a typical performance metric for real-time databases is the number of transactions that miss their deadline.

eXtremeDB/rt implementation of deterministic ACID real-time transactions

eXtremeDB/rt provides semantics for passing a transaction’s deadline and priority to the database scheduler. Transactions are then scheduled either through the Earliest Deadline First (EDF) or Priority Inheritance (PI) algorithms (the schedule is serializable — “read-write” transactions are executed sequentially, “read-only” in parallel). Once scheduled, the eXtremeDB/rt transaction manager implementation enforces firm deadlines through utilizing a deterministic rollback policy. Data modifications or retrieval are allowed only if they are able to finish the within the transaction’s set deadline. “Late” transactions are identified, interrupted and forced to initiate rollback in time to satisfy set deadlines. The key is to ensure that all database runtime internals are in a “recoverable” condition. The database kernel reserves enough time out of the given transaction deadline to rollback modifications made to the point of interruption. We can prove that, at the control point, a transaction’s rollback time is less than the time the transaction has spent modifying the database, or searching through the database.

The eXtremeDB/rt transaction manager

The database transaction manager has a number of verification checkpoints in the code at which the transaction elapsed time is tested against the deadline. The frequency of the verifications eliminates the possibility of executing the database code long enough to miss the set deadline. If the control point is reached (the transaction ran out of the allotted time slice), the transaction is assigned a special “transaction interrupted” status and the control is returned back to the application. The application is then expected to rollback (abort) the transaction. The transaction manager ensures that all database runtime internals are in a “recoverable” condition. The subsequent transaction rollback will restore the database to the consistent state that existed prior to the start of the transaction. Crucially, the transaction manager guarantees that the rollback will be completed within the deadline, provided that the application initiates the rollback when signaled to do so by the database runtime. Thus, the transaction would miss the deadline, but not be “late” and the internal consistency of the database is preserved.

Chart of the eXtremeDB/rt database transaction scheduler

Related Resources

Documentation & Collateral

b

Review the eXtremeDB/rt data sheet

U

Learn more about eXtremeDB/rt in our on-line documentation

To Err is Human. The Case for Buy Over Build in Hard Real-time Database Management Systems

t

eXtremeDB/rt Q & A: what distinguishes a true real-time database?

eXtremeDB/rt offers deterministic ACID-compliant transactions
Real-time transaction timeline

Chart from the white paper, “Real-time Deterministic Database Management” about the objectives of deterministic, predictable database management in the context of real-time application design.

In the News

Tailored to your needs


The nature of eXtremeDB/rt’s tight integration with the RTOS and target hardware requires that each evaluation package be assembled uniquely for your needs.  Please contact us so that we can gather information on your RTOS vendor, version, target hardware, tool chain, and so on.

View the ever-expanding list of supported real-time operating systems.

Send us an email

Give us a call

+1-425-888-8505

Desktop distributions

Free desktop evaluation packages of eXtremeDB/rt for Linux, MacOS, QNX and Windows platforms are available for immediate no-hassle download. Learn more about the programming interface and various real-time and non-real-time features of eXtremeDB/rt. After you have tried the desktop version, we hope you’ll contact us for a free trial of eXtremeDB/rt tailored to the needs of your RTOS.

You are also welcome to contact us, and we will send you a download of eXtremeDB/rt running in the FreeRTOS simulator.

News and articles about real-time database management.

COTS Cover photo July 2022

"Soft v Hard Real-time Systems" Embedded Computing, November 4, 2022

Real-time transaction timeline

"Embedded Databases in Real-Time Systems" CircuitCellar.com, March 14, 2022

Steve Graves, President and CEO, McObject

"Embedded Executive: Steve Graves, President and CEO, McObject" EmbeddedComputing.com, January, 2022 An interview reviewing key concepts in real-time computing.

COTS article about eXtremeDB/rt

"Databases in Hard Real Time" McObject Launches True Real-Time Deterministic Database for embOS Real-time Operating System Applications, Wilmott.com, October 15, 2021

COTS article about eXtremeDB/rt

"Keeping A Mission-Critical Deterministic DBMS On Time" by McObject CTO Andrei Gorine EmbeddedComputing.com, September 20, 2021

COTS article about eXtremeDB/rt

"Real time tasks need real time data" Read the Wind River blog, September 7, 2021

We’re grateful for the partnerships we have with industry leaders, and invite you to read what they say about eXtremeDB/rt in our joint press releases.

Azure RTOS ThreadX

“Managing data with a hard real-time requirement is a challenge for developers,” comments Tony Shakib, Partner General Manager, Microsoft Azure IoT. “Developers have had to use current solutions that may not meet time constraints or write their own database system. eXtremeDB/rt brings a solution to Microsoft Azure developers that eliminates this trade off.”

Read the joint press release.

DDC-I’s Deos

eXtremeDB/rt provides an excellent option for developers of resource-constrained, mission-critical embedded systems who require a compact, real-time embedded database,” said Greg Rose, vice president of marketing and product management at DDC-I. “We look forward to working with McObject to offer eXtremeDB/rt to embedded developers utilizing our Deos real-time operating system.”

Read the joint press release.

embOS from SEGGER

SEGGER’s CEO, Ivo Geilenbruegge, had this to say: “We are excited that McObject has created a first-of-its-kind real-time database system to complement our embOS RTOS and extend support for hard real-time systems to include database operations. Real-time systems are following the trend of embedded systems in that they are being called upon to manage more (and more complex) data.”

Read the joint press release.

FreeRTOS

Richard Barry, FreeRTOS founder, said “It is good to have another high-quality option for FreeRTOS users, this time providing a real-time deterministic database which can, as just one example, fulfill a crucial role in the Industrial Internet of Things (IIoT): data collection, aggregation, and distribution in oil rig blow-out prevention (BOP) systems. A BOP is a specialized device equipped with sensors to detect a “kick” and actuate valves to prevent a catastrophic blowout.” Richard continued, “The need to detect and respond within deadlines is emblematic of real-time industrial systems.”

Read the press release.

INTEGRITY from Green Hills Software

Joe Fabbre, Global Technology Director for Green Hills had this to say: “McObject has created a unique real-time database that complements our INTEGRITY RTOS and extends hard real-time support to database operations. Advanced applications in real-time systems are being called upon to manage more (and more complex) data. eXtremeDB/rt gives developers of these systems an off the shelf solution for real-time data management.”

Read the joint press release.

LynxOS

“We were delighted to work with McObject to bring eXtremeDB/rt to the LynxOS partner ecosystem. Our companies share the vision that real-time systems are becoming more sophisticated and consequently have to manage more complex data. eXtremeDB/rt fills a critical gap in the technology stack,” said Pavan Singh, VP of product management, Lynx Software Technologies.

Read the joint press release.

QNX Neutrino RTOS

“Real-time performance can benefit embedded software developers in many market segments including autonomous systems, industrial control, robotics and medical devices,” said Romain Saha, Strategic Alliances Director at BlackBerry QNX: “McObject builds upon many years of QNX support by bringing eXtremeDB/rt to the latest version of the QNX Software Development Platform.”

Read the joint press release.

SIEMENS Nucleus RTOS

“McObject’s eXtremeDB/rt allows Nucleus customers to have a truly embedded database solution that allows them to meet the determinism they require in a commercial-off-the-shelf solution.” said Jeff Hancock, Siemens Embedded Senior Product Manager. “eXtremeDB/rt helps Nucleus customers manage ever-growing data requirements.”

Read the joint press release.

WindRiver VxWorks

“Through our work with McObject, we’re helping customers modernize and accelerate the delivery of reliable intelligent systems that demand real-time requirements,” said Michel Chabroux, Senior Director, Product Management, Wind River. “We look forward to building on our proven track record of success with McObject to help advance the next generation of cloud-connected intelligent systems with increasingly challenging edge compute needs.”

Read the joint press release.