An in-memory database stores its data inside main memory instead in a persistent source. In memory databases are significantly faster than conventional database management systems because they reduce the bottleneck of transferring data from disk into memory by storing the data directly in memory.
In-memory databases store data on volatile storage media. When the power to the device is interrupted or reset, these memories lose all stored information. Therefore, in-memory databases are by default not ACID compliant.
The database developers created mechanisms to guarantee the durability of in-memory database systems. They are using snapshots and logs that are periodically written to the persistence layer (disk).
Use Cases for In-Memory databases
In critical applications where real-time data is required, the use of in-memory databases is absolutely necessary.