An in-memory database (IMDB) is a computer system that stores and retrieves data records that reside in a computer’s main memory, e.g., random-access memory (RAM). With data in RAM, IMDBs have a speed advantage over traditional disk-based databases that incur access delays since storage media like hard disk drives and solid-state drives (SSD) have significantly slower access times than RAM. This means that IMDBs are useful for when fast reads and writes of data are crucial.
IMDBs work by keeping all data in RAM. That is the medium in which data is stored in RAM versus disks or SSDs. IMDBs essentially replace the disk-accessing component of disk-based databases with RAM accesses. In some IMDBs, a disk-based component remains intact, but RAM is the primary storage medium. Since RAM is volatile (e.g., data is lost if the computer loses power), some IMDBs also store data on disk as a preventative measure to minimize the risk of data loss.
Most IMDBs also guard against data loss in a single data center (a capability known as “high availability”) by keeping copies (“replicas”) of all data records in multiple computers in a cluster. This data redundancy ensures that any data record will not be lost upon failure of any given computer.
An example use case would be a high traffic eCommerce site that needs to store shopping cart contents for hundreds of thousands of customers at any given time. Response times at that scale would be too slow for many disk-based databases, so IMDBs are used to keep up with the load and ensure a positive customer experience.
Another use case entails business intelligence (BI) analytics, in which data is retrieved and presented in a visual way (i.e., in dashboards). Many types of business users want to see data presented in multiple ways, as well as to drill down into greater data detail. To do so efficiently, they leverage an in-memory database that can quickly deliver data so users spend more time analyzing and making decisions, and less time waiting for the system to respond.
