From Chaos to Control: Addressing Shard Distribution Challenges in M3DB with Subclusters

2026-09-09

Uber redesigned M3DB's shard placement for large clusters by partitioning nodes into self-contained subclusters that own non-overlapping portions of the shard space. The approach reduces failure and maintenance blast radius, allows operations on separate subclusters to run in parallel, and uses a greedy migration algorithm to keep shard distribution balanced during scaling.