In-memory database
An in-memory database (IMDB; also main memory database system or MMDB) is a database management system that primarily relies on main memory for computer data storage. It is contrasted with database management systems which employ a disk storage mechanism. Main memory databases are faster than disk-optimized databases since the internal optimization algorithms are simpler and execute fewer CPU instructions. Accessing data in memory provides faster and more predictable performance than disk. In applications where response time is critical, such as telecommunications network equipment, main memory databases are often used.[1]
ACID support
In their simplest form, main memory databases store data on volatile memory devices. These devices lose all stored information when the device loses power or is reset. In this case, MMDBs can be said to lack support for the durability portion of the ACID (atomicity, consistency, isolation, durability) properties. Volatile memory-based MMDBs can, and often do, support the other three ACID properties of atomicity, consistency and isolation.
Many MMDBs add durability via the following mechanisms:
- Snapshot files, which record the state of the database at a given moment in time. These are normally generated when the MMDB does a controlled shut-down, or on request, and thus while they give a measure of persistence to the data (in that not everything is lost in the case of a system crash) they only offer partial durability (as 'recent' changes will be lost). For full durability, they will need to be supplemented by one of the following:
- Transaction Logging, which records changes to the database in a journal file and facilitates automatic recovery of an in-memory database.
- Non-volatile RAM, usually in the form of static RAM backed up with battery power (battery RAM), or an electrically erasable programmable ROM (EEPROM). With this storage, the MMDB system can recover the data store from its last consistent state upon reboot.
- High Availability implementations that rely on database replication, with automatic failover to an identical standby database in the event of primary database failure. To protect against loss of data in the case of a complete system crash, replication of a MMDB is normally used in conjunction with one or more of the mechanisms listed above.
Some MMDBs allow the database schema to specify different durability requirements for selected areas of the database - thus, faster-changing data that can easily be regenerated or that has no meaning after a system shut-down would not need to be journalled for durability (though it would have to be replicated for high availability), whereas configuration information would be flagged as needing preservation.
"Hybrid" in-memory/on-disk databases
The first database engine to support both in-memory and on-disk tables in a single database was released in 2003.[2] The advantage to this approach is flexibility: the developer can strike a balance between performance (which is enhanced by sorting, storing and retrieving specified data entirely in memory, rather than going to disk); cost, because a less expensive hard disk can be substituted for more memory; persistence; and form factor, because RAM chips cannot approach the density of a small hard drive.
Manufacturing efficiency is another reason a combined in-memory/on-disk database system may be chosen. Some device product lines, especially in consumer electronics, include some units with permanent storage, and others that rely on memory for storage (set-top boxes, for example). If such devices require a database system, a manufacturer can adopt a hybrid database system at lower cost, and with less code customization, than using separate in-memory and on-disk databases, respectively, for its disk-less and disk-based products.
Commercial products
In recent years, main memory databases have attracted the interest of larger database vendors. TimesTen, a start-up company founded by Marie-Anne Neimat in 1996 as a spin-off from Hewlett-Packard, was acquired by Oracle Corporation in 2005. Oracle now markets this product as both a standalone database and an in-memory database cache to the Oracle database. IBM acquired SolidDB in 2008, and Microsoft is widely rumored to be launching an in-memory solution in 2009.[3]
Products
| Product name | License | Description |
|---|---|---|
| Adaptive Server Enterprise (ASE) 15.5 | commercial/enterprise database from Sybase)[4] | |
| Apache Derby | ||
| Altibase | commercial product, has in-memory and disk table; HYBRID DBMS | |
| BlackRay | open source | |
| CSQL | dual licensing | |
| Datablitz | DBMS | |
| H2 | open source | has a memory-only mode |
| HSQLDB | open source | has a memory-only mode |
| InfoZoom | in-memory BI and data analysis | |
| membase | open source | NoSQL, hybrid |
| MicroStrategy | in-memory BI for MicroStrategy 9 | |
| MonetDB | open source | |
| MySQL | has a cluster server which uses a main-memory storage engine | |
| Oracle Berkeley DB | can be configured to run in memory only | |
| Panorama | for Windows and Macintosh, both single user and server versions | |
| Polyhedra IMDB | relational, supports High-Availability; acquired in 2001 by ENEA | |
| QlikView | BI-tool developed by QlikTech | |
| RDM Embedded | including hybrid | |
| RDM Server | including hybrid | |
| Redis | open source | NoSQL |
| solidDB by IBM | including hybrid, HSB-based HA, Shared memory, embedded, XA, etc. | |
| SQLite | open source | hybrid, RAM and disk dbs can be used together |
| Starcounter | in-memory object relational dbms | |
| TimesTen by Oracle | ||
| VoltDB | in-memory | |
| TREX | search engine in the SAP NetWeaver integrated technology platform produced by SAP AG | |
| Xcelerix by Frontex | commercial product |
References
- ^ "TeleCommunication Systems Signs up as a Reseller of TimesTen; Mobile Operators and Carriers Gain Real-Time Platform for Location-Based Services". Business Wire. 2002-06-24.
- ^ "Solid Announces General Availability of BoostEngine 4.0, the First On-Disk/In-Memory Hybrid Database Manager" (Press release). PR Newswire. 2003-04-28.
- ^ http://www.intelligententerprise.com/channels/business_intelligence/showArticle.jhtml?articleID=210700171
- ^ http://www.sybase.com/products/databasemanagement/adaptiveserverenterprise
- Jack Belzer. Encyclopedia of Computer Science and Technology - Volume 14: Very Large Data Base Systems to Zero-Memory and Markov Information Source. Marcel Dekker Inc. ISBN 0-8247-2214-0.
See also
- In Memory Data Grid - In Memory Distributed Data management
- NoSQL - Alternative Scale-out Databases