What is FlockDB?
FlockDB is an open source, fault-tolerant, and distributed graph database licensed under the Apache license for managing data at webscale. Twitter used it to build user database and manage relationships. It can be efficiently used in high throughput and low latency environments. FlockDB was created by Twitter for relationship related analytics. FlockDB is a database that stores graph data which is optimized for very large adjacency lists, and quick reads and writes but not optimized for graph traversal operations.
In FlockDB, graphs are stored as sets of edges between nodes which are identified by 64 bit integers. Each edge between nodes is also marked with a 64 bit position. Edge can be used for sorting. For social graphs, integer node IDs will be user IDs while in a graph containing favorite tweets, the destination will be a tweet ID.