LevelDB

LevelDB is a storage engine developed by Google in 2011, which Bitcoin uses to store and manage essential data and transactions. Before LevelDB, Bitcoin used Berkeley DB, but it switched to LevelDB in 2011 to enhance its technical performance and increase its scalability.

LevelDB stores data as key-value pairs, which means each piece of data is stored with a unique key that can be quickly found when needed. This method allows for very fast data operations, making LevelDB capable of handling many transactions at once. The data is written to an in-memory structure first and then saved to physical disks in a way that optimizes reading and writing speeds.