A high-speed relational database system designed for embedded use
Polyhedra IMDB is a high-speed, in-memory, relational database system. It takes responsibility for preserving and making accessible the data needed by the component parts of an embedded system, freeing up developers to concentrate on the features that distinguish their products with capabilities like:
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In-memory for high performance
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Standards-based to ease adoption costs
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ACID-compliant transactions
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Standalone or fault-tolerant configurations
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Triggers and active queries for enhanced responsiveness
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Client-server for protection and to allow remote access
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Polyhedra IMDB is an in-memory, relational database system, designed for use in embedded systems.
Polyhedra IMDB is a database system (DBMS). It stores information with a well-defined interface for retrieving and updating it. It isolates the application writers from the details of data storage: they do not need to know how it is preserved, or the format of data on the storage media.
Polyhedra is a relational DBMS. This is the most widely-known, and widely-adopted database model. Basically, data is stored in named tables; each table has a number of named columns (‘attributes’), each with an associated data type, and each row in the table corresponds to a data record. Polyhedra is SQL based - again, the most widely-used language for setting up, querying and manipulating databases.
In common with other relational database systems Polyhedra is ‘transactional’. This means that operations are grouped together and applied atomically: the mid-transaction state is invisible to other applications, and if a transaction fails, the database ‘rolls back’ to the state it was in before. As the database system enforces these properties, even over system failure, applications do not have to worry about data consistency.
Like other relational database systems, databases in Polyhedra are flexible. Not only can tables be added or dropped on the fly, but it is also possible to add and drop individual columns, without affecting running applications (if they are not using these columns). As Polyhedra uses a familiar, transactional data model, with familiar interfaces (SQL, ODBC and JDBC), is it easy for people to adopt it.
Polyhedra IMDB is an in-memory DBMS. Keeping all data in store means that queries and updates are very fast! Polyhedra IMDB uses a system of snapshots and journal logs to ensure that data is preserved, without excessive ‘disk-rattle’.
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Lockheed Martin UK
Enea’s Polyhedra Accelerates Development and Deployment for Lockheed Martin Helicopter Project. Read More.
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For even faster performance, it is possible to designate individual tables - and even individual columns in a table - as ‘transient’; if a transaction only affects transient data, the journal log is not written to file.
Polyhedra IMDB is fully-client server, and the communication protocols are platform-independent. In addition, the database files are fully portable, so a file generated on a host platform can be used as the seed for a database running on a different target platform regardless of issues such as endian mismatch. Polyhedra is standards-based, and the main client libraries are ODBC (for C/C++ programmers) and JDBC (for Java).
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- Standards-based: use of SQL, ODBC and JDBC eases adoption costs
- Polyhedra software runs in ‘user space’ and does not need any kernel modifications, special privileges or special installation.
- High-speed queries and updates, with durability achieved via a low-overhead transaction journal
- Simplified transactional model which is tuned for performance
- Active queries keep clients up to date without the need for polling; active trigger code enforces integrity and performs ‘knock-on’ changes
- Hot-standby configurations supported, for use in high-availability systems
- Allows trigger code to be attached to a database, which runs as part of the transaction that triggered it
- There is even a “don’t tell me too often” feature, allowing the client to specify a minimal interval between updates: for a graphical display, the client might set this to 1/10th of a second to reduce flicker
- Uses a client-server model that protects the data and allows for remote access via TCP
- Supports attaching business logic directly to the database thus reducing the work that needs to be done by the client applications (and the amount of code that needs to be written by the developers, and thus the number of bugs!), and improves overall performance and data integrity
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Polyhedra IMDB and Polyhedra FlashLite
Polyhedra is a family of DBMS products, sharing very similar functionality. The two main products are Polyhedra IMDB and Polyhedra FlashLite. Both are relational database systems, sharing the same SQL engine, the same client server architecture and protocols, and both support the hot-standby model for use in high-availability systems. The primary difference between the two is in how they hold and preserve data:
- Polyhedra IMDB holds the working copy of a database in memory. Data is preserved by means of on-demand snapshots, supplemented by a journal-logging mechanism: at the end of each successful transaction that altered persistent data, a journal record is appended to the snapshot file, recording what was changed in the transaction. When the system starts up, the shapshot is read, and then all appended journal records are applied (up to, but not including, the first incomplete or corrupted record).
- Polyhedra FlashLite holds the data in a file (assumed to be on a flash filing system) with a configurable-sized RAM cache. A technique known as ‘shadow paging’ is used to ensure transactions are atomic and durable: the database file is treated as a series of pages, with a page map allowing logical pages to be relocated within a file. When a transaction alters a logical page, the updated version is written to a spare page; at the end of the transaction, the modified page maps are written out, and the pages that hold the old versions of data are marked as spare. If the system fails before the updated maps are written out, the database can use the old version of the maps to recover the previous state.
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As Polyhedra FlashLite and Polyhedra IMDB are essentially identical from the application writers’ point of view - and even use exactly the same client libraries, the decision as to whether to use one or the other boils down to the issues of footprint and performance:
- Polyhedra IMDB needs more RAM, but offers greater performance when updating the database
- Polyhedra FlashLite can run in as little as 1MB or RAM (for code and cache), though it can be configured with a larger cache to speed up the performance, particularly for queries and large transactions.
The compatibility between the two products is so high that it is even possible to start up a FlashLite database using a saved Polyhedra IMDB database as a seed, or to run a Polyhedra FlashLite server as a standby to a Polyhedra IMDB server - making it possible to migrate a fault-tolerant system using Polyhedra IMDB to one using Polyhedra FlashLite technology with zero downtime.
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Green Hills Software, Inc., is a technology leader in high performance compilers, software development tools and real-time operating systems (RTOS) for developers of embedded systems.
Wind River is the global leader in device software optimization (DSO). We enable companies to develop, run, and manage device software better, faster, at lower cost, and more reliably.
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