TokuDB

"TokuDB is an open source, high-performance storage engine for MySQL and MariaDB. It achieves this by using a Fractal tree index. It is scalable, ACID and MVCC compliant, provides indexing-based query improvements, offers online schema modifications, and reduces slave lag for both hard disk drives and flash memory.

TokuDB is included in Percona Server, MariaDB and nagius based opmon.

TokuDB uses a Fractal tree index tree data structure that keeps data sorted and allows searches and sequential access in the same time as a B-tree but with insertions and deletions that are asymptotically faster than a B-tree. Fractal Trees also allow for messages to be injected into the tree in such a fashion that schema changes (such as adding or dropping a column, or adding an index) can be done online and in the background.^[3] As a result, more indexes can be maintained without a drop in performance. This is because adding data to indexes tends to stress the performance of B-trees, but performs well in Fractal Tree indexes.

Fractal Tree indexes can be applied to a number of applications characterized by near-real time analysis of streaming data. They can be used as the storage layer of a database or as the storage layer of a file system. When used in a database, they can be used in any setting where a B-tree is used, with improved performance. Examples include: network event management, online advertising networks, clickstream analytics, and air traffic control management.^[5] Other uses include accelerated crawler performance for search engines for social media sites. It can also be used to create indexes and columns online, enabling query flexibility for e-commerce personalization. It is also suited to improving performance and reducing existing loads on transactional websites. In general, it performs well in applications that must simultaneously store log file data and execute ad hoc queries."

https://en.wikipedia.org/wiki/TokuDB

https://github.com/percona/tokudb-engine

https://www.percona.com/software/mysql-database/percona-tokudb

https://archive.fosdem.org/2016/schedule/event/tokudb/