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S2 Geometry Library (Google)

S2 (s2geometry.io) is Google's open-source spatial indexing library that divides the surface of a sphere (Earth) into hierarchical cells via a space-filling Hilbert curve. Each cell has a unique 64-bit S2 Cell ID that can be used as a shard key for geospatial systems. (Source: sources/2024-03-14-highscalability-brief-history-of-scaling-uber)

Used by Uber as the original shard-key substrate for the 2014 dispatch rewrite — S2 cell IDs partitioned cities into areas of consideration, letting the matching state be distributed across Ringpop-gossiping dispatch nodes. Later superseded at Uber by the open-sourced hexagonal H3 successor.

Seen in

• sources/2024-03-14-highscalability-brief-history-of-scaling-uber — cited as the original Uber dispatch shard key, later replaced by H3.

Related

• systems/h3-geo — Uber's hexagonal successor.
• systems/uber-dispatch — primary Uber consumer.
• concepts/geospatial-sharding — the sharding pattern S2 cell IDs implement.