What is CRDT support in Redis and how does it relate to Active-Active geo-distribution?

CRDTs (Conflict-free Replicated Data Types) are data structures that can be replicated across nodes and updated independently, with a mathematically guaranteed merge algorithm that resolves conflicts without coordination. They are used in Redis Enterprise's Active-Active (formerly CRDT) geo-distribution feature, where multiple Redis databases exist in different geographic regions and all accept writes simultaneously. Each region handles local writes at low latency; changes are asynchronously replicated to other regions. When concurrent writes to the same key happen in two regions, the CRDT algorithm deterministically resolves the conflict — for counters, both increments are summed; for sets, the union is taken; for LWW (Last-Write-Wins) registers, the highest-timestamp value wins. This provides multi-master replication with local read/write latency across datacenters. Open-source Redis does not include CRDT support; it is a Redis Enterprise feature for globally distributed applications.