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Paper review. Sharding the Shards: Managing Datastore Locality at Scale with Akkio

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This paper by Facebook, which appeared in OSDI'18, describes the data locality management service, Akkio. Akkio has been in production use at Facebook since 2014. It manages over 100PB of data, and processes over 10 million data accesses per second.

Why do we need to manage locality?  Replicating all data to all datacenters is difficult to justify economically (due to the extra storage and WAN networking costs) when acceptable durability and request serving latency could be achieved with 3 replicas. It looks like Facebook had been doing full replication (at least for ViewState and AccessState applications discussed in the evaluation) to all the 6 datacenters back-in-the-day, but as the operation and the number of datacenters grew, this became untenable.

So, let's find suitable home-bases for data, instead of fully replicating it to all datacenters. But the problem is access locality is not static. What was a good location/configuration for the data ceases to become suitable wh…

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