MyRocks: LSM-tree database storage engine serving Facebook's social graph

Facebook uses MySQL to manage tens of petabytes of data in its main database named the User Database (UDB). UDB serves social activities such as likes, comments, and shares. In the past, Facebook used InnoDB, a B+Tree based storage engine as the backend. The challenge was to find an index structure using less space and write amplification [1]. LSM-tree [2] has the potential to greatly improve these two bottlenecks. RocksDB, an LSM tree-based key/value store was already widely used in variety of applications but had a very low-level key-value interface. To overcome these limitations, MyRocks, a new MySQL storage engine, was built on top of RocksDB by adding relational capabilities. With MyRocks, using the RocksDB API, significant efficiency gains were achieved while still benefiting from all the MySQL features and tools. The transition was mostly transparent to client applications.

Facebook completed the UDB migration from InnoDB to MyRocks in 2017. Since then, ongoing improvements in production operations, and additional enhancements to MySQL, MyRocks, and RocksDB, provided even greater efficiency wins. MyRocks also reduced the instance size by 62.3% for UDB data sets and performed fewer I/O operations than InnoDB. Finally, MyRocks consumed less CPU time for serving the same production traffic workload. These gains enabled us to reduce the number of database servers in UDB to less than half, saving significant resources. In this paper, we describe our journey to build and run an OLTP LSM-tree SQL database at scale. We also discuss the features we implemented to keep pace with UDB workloads, what made migrations easier, and what operational and software development challenges we faced during the two years of running MyRocks in production.

Among the new features we introduced in RocksDB were transactional support, bulk loading, and prefix bloom filters, all are available for the benefit of all RocksDB users.