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Mimer SQL Real-Time Edition - White Paper 1(5)

Mimer SQL Real-Time Edition – White Paper
- Dag Nyström, Product Manager Mimer SQL Real-Time Edition

Mimer SQL Real-Time Edition is a predictable, scalable and zero maintenance
database management system for embedded real-time systems, such as automotive,
process-control, and robotic applications. By combining predictable hard real-time and
non-real-time database access, integrated data management solutions impossible to
implement with other DBMS products on the market are made possible.

Mimer SQL Real-Time Edition allows data
management in embedded real-time applications to be
taken to a higher level while still maintaining real-time
predictability and fine-grained control.
The uniqueness of Mimer SQL Real-Time Edition
comes from its real-time access methods featuring fine-
grained in-memory real-time data access with ultra-
short, fully deterministic response-times. These real-time
algorithms stems from well-proven academic research
results gained from years of collaboration with academia
(Mälardalen Real-Time Research Center,
http://www.mrtc.mdh.se).
In Mimer SQL Real-Time Edition, real-time and non-
real-time data can be safely modeled and shared by
both time-critical and administrative processes, such as
Embedded hard real-time
diagnostics, statistics and maintenance. A common
databases are needed in many
solutions for automotive, process approach for sharing data between real-time and non-
industry and various embedded
real-time processes is to manage real-time data
devices.
separately using in-house, specialized data storages.
These storage solutions often result in time-consuming
development and maintenance, poor system scalability
and longer time to market. By using Mimer SQL Real-
Time Edition, all data in the system can be modeled in
one uniform data storage using standard modeling
techniques. Of course, the other strong arguments for
using Mimer SQL, such as a footprint of 300kb or less,
zero maintenance, multi-user data access, and full
support for ISO/ANSI SQL still remains.

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Real-Time Access using Database Pointers
Mimer SQL Real-Time Edition utilizes a unique real-time access concept called database
pointers, which allow predictable, fine-grained access to data within the database. Database
pointers are in-memory application variables that can be initialized to point at individual or sets of
data elements in the database. At run-time, these pointers can be read and updated with
predictable response-times that are 1000 times faster, or more, than traditional database calls.
The API allows database pointers to be dynamically created and deleted during run-time, but
could be customized for static use if necessary. Access to data using database pointers need no
index-lookups or statement compiling, instead pointers locate the data immediately. The integrity
of the database is retained due to that the database pointer API ensures type checking and
concurrency. To put it simple; “Database pointers combine the performance and predictability of
shared variables with the power of an SQL database.”
It is safe to say that Mimer SQL Real-Time Edition once and for all invalidates the
misconception that databases are slow, bulky and unpredictable pieces of software.

Figure 1: Overview of the Mimer SQL Real-Time Edition API's

Safe Sharing of Real-Time Data
The true benefit of Mimer SQL Real-Time Edition is its ability to safely share data between
both real-time and administrative applications. In Mimer SQL Real-Time Edition, all application
data can be stored in one single database, using any relational modeling technique to optimize
performance and memory consumption. After that, data that is needed by (hard) real-time
applications in the system can be elevated to become real-time data. This implies that the
database manager will create an in-memory copy of the data and enable it for real-time access.
This data can then be accessed using database pointers for guaranteed real-time predictability,
but can also be accessed using standard SQL query management just as any data in the
database. A special real-time concurrency-control algorithm ensures that the real-time data
access is never blocked or aborted because of conflicts with other database accesses.
Furthermore, Mimer SQL Real-Time Edition adopts the scheduling and critical section policies
from the underlying real-time operating system, i.e., if your operating system uses the immediate
inheritance protocol, so will the database pointers. By limiting the maximum blocking times of
data access, standard response-time analysis methods can be used.

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Real-Time Data and Event Logging
Since most applications today involve some kind of logging and diagnostics, Mimer SQL
Real-Time Edition directly supports this. By introducing multirow and multicolumn database
pointers it has never been easier to record logs and events, as well as handle producer-
consumer type applications. By using multirow database pointers, all (or some if desired) records
in a table can be circularly accessed. Before each write operation on the database pointer, the
pointer is redirected to the same column in the next record of the table. Combining this with
multicolumn database pointers, several columns can be written in one operation. In Figure 2, a
combination of a multirow and multicolumn database pointer is used to store warnings and errors
in a log-table. When the table is full, the pointer continues to the first record again, overwriting
that log. During run-time, administrative applications can directly access the entire table using
SQL queries under transactional control. Of course, the predictable real-time properties of
database pointers are retained in both multirow and multicolumn database pointers.

Figure 2: A multirow multicolumn database pointer used in a logging table

Retained Real-Time Application Control
Another common misconception about databases is that, apart from databases being bulky,
you give up control of the application to the database. With Mimer SQL Real-Time Edition, all
real-time operations are performed entirely in primary memory using the caller’s thread of
execution instead of using a client/server architecture. Thus, real-time operations will never yield
a context switch for data accesses. If persistency of all or some data is needed, you decide when
or if to flush real-time data to secondary storage such as a hard disk drive or a flash memory.
Flushing data will, of course, never block real-time data access. To be able to select flushing
strategy for individual real-time data elements greatly improves performance, since much real-
time data might never need to be saved to persistent storage.

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Achieve True Application Interoperability
Mimer SQL Real-Time Edition has inherited all the functionality from the other members of
the Mimer SQL product family, which for example include 100% conformance to international
SQL standards. This implies that Mimer SQL Real-Time Edition will work seamlessly with any
standard database tool, as well as making porting of your existing applications easier.
All products in the Mimer SQL family are characterized by zero maintenance, high
performance and full multilingual support. This gives you a very low total cost of ownership (TCO)
for your database solution, disregarding if you distribute a low priced - high volume product or if
you deploy a high priced – low volume product.

Customization to Your Needs
Mimer Information Technology AB has a long experience of customization and porting their
products for various requirements and environments. All Mimer´s products stem from the same
code-base and can be tailored for systems ranging from tiny real-time control-nodes to resource
abundant enterprise servers.
Mimer SQL Real-Time Edition can be made available for a range of operating systems, both
general operating systems and RTOS’s. Evaluation versions for MS Windows, Windows CE,
Linux, and VxWorks are currently available upon request. For other platforms, please contact us.

Mimer SQL Real-Time Performance
Data type Intel Core2Duo 2.33GHz Intel XScale, 533 MHz
Read Write Read Write
Integer (32bit) 0.14µs 0.11µs 1.6µs 1.2µs

Integer (16bit) 0.10µs 0.10µs 1.1µs 1.0µs

String (100bytes) 0.15µs 0.36µs 1.7µs 2.6µs
Timestamp 0.18µs 0.19µs 2.1 µs 2.3 µs

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Facts About Mimer SQL Real-Time Edition
Footprint
Full Real-Time Server (Engine) <20 kb + Ordinary Mimer SQL Engine server (~3.5 Mb)
Embedded Real-Time Server <10 kb + Ordinary Mimer SQL Embedded server (from ~300kb)

Real-Time Client API <35 kb + communication package (configurable 2kb – 160kb)

Datatypes (can be extended on demand)
Integer (32bit), Integer (16bit), String, Timestamp
Persistence
In-Memory with option to flush to persistent storage
Real-time operations
Single value database pointers Read/Write individual database values.

One database pointer per value

Multicolumn database pointers Atomic Read/Write of multiple columns (attributes) of a database
record.

One database pointer per record

Multirow database pointers Read/Write of database value in multiple database records of a
table.

Writes are performed in sequential order

Reads are performed in sequential, backwards or arbitrary order.

Can be combined with multicolumn functionality

One database pointer per table

Database pointer flushing Flushing of any database pointer to persistent storage.

Will not block real-time operations.

For further information, contact the author:

Dag Nyström,
Product Manager, Mimer SQL Real-Time Edition
Mimer Information Technology AB
Uppsala, Sweden
Mail: dag.nystrom@mimer.com

or our sales department:
Mimer Information Technology AB
Uppsala, Sweden
mail: info@mimer.com
Phone: +46 (0)18 780 92 00
Web: http://www.mimer.com

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