Sharding the Shards: Managing Datastore Locality at Scale with Akkio

Akkio is a locality management service layered between client applications and distributed datastore systems. It determines how and when to migrate data to reduce response times and resource usage. Akkio primarily targets multi-datacenter geo-distributed datastore systems. Its design was motivated by the observation that many of Facebook's frequently accessed datasets have low R/W ratios that are not well served by distributed caches or full replication. Akkio's unit of migration is called a u-shard. Each u-shard is designed to contain related data with some degree of access locality. At Facebook u-shards have become a first-class abstraction.

Akkio went into production at Facebook in 2014, and it currently manages over 100PB of data. Measurements from our production environment show that Akkio reduces access latencies by up to 50%, cross-datacenter traffic by up to 50%, and storage footprint by up to 40% compared to reasonable alternatives. Akkio is scalable: it can support trillions of u-shards and process many 10's of millions of data access requests per second. And it is portable: it currently supports five datastore systems.