Last-write-wins can erase another user's edit#
Two concurrent inserts
Initial: cat
User A inserts "s" at start → scat
User B inserts "!" at end → cat!When both edit from the same version, applying raw character positions in different orders can diverge or misplace intent. The system needs operation identity, version context, reconnect behavior, and a chosen convergence model.
Presence is ephemeral, while document operations and snapshots need durable recovery. OT and CRDTs are solution families; knowing why concurrency is hard matters more for a general interview than implementing either algorithm.
Related practice problems
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