FlockDB

FlockDB is used on Twitter to store social graphs, meaning the relations between various users.

FlockDB was meant to hold little depth levels, but to be able to scale horizontally. This means it can store a small number of relations and relation types between users, but it can work with a huge amount of users (nodes).

It's considered a best practice to use the Gizzard framework, another tool developed by Twitter, to query for data stored on a FlockDB database.

Comparing FlockDB to other graph database engines like Neo4J or OrientDB, FlockDB is much simpler in structure, works faster than all of them, but can't handle a high level of data depth.

Features:

• Built for speed
• Supports arithmetic queries
• Can work with millions of entries
• Archive and restore edges
• Support for database replication
• Online data migration

Requirements:

• Java 1.6 or higher
• sbt 0.7.4 or higher
• Apache Thrift 0.2.0 or higher