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 among both
real-time and administrative applications. Mimer SQL Real-Time Edition real-time data, accessed using
database pointers, is accessed using standard SQL query management just as any data. Concurrency-control
lgorithms ensure that real-time data access is never starved 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.
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 circular database pointers and multi-column database pointers
it has never been easier to record logs and events, as well as handle producer-consumer type applications.
By using circular 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 multi-column database pointers, several columns can be written
in one operation. In Figure 2, a combination of a circular and multi-column 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 circular and multi-column database pointers.
Figure 2: A circular multi-column database pointer for 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.
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.
