Sharding the Shards: Managing Datastore Locality at Scale with Akkio

USENIX Symposium on Operating Systems Design and Implementation (OSDI)


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 µ-shard. Each µ-shard is designed to contain related data with some degree of access locality. At Facebook, µ-shards have become a first-class abstraction.

Akkio went into production at Facebook in 2014, and it currently manages ∼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 µ-shards and process many 10’s of millions of data access requests per second. And it is portable: it currently supports five datastore systems.

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