HLD-308·Messaging & Fan-out
Hard · 1,500 ptsMultiplayer Document Cursor & Operation Relay
Design a real-time collaborative document backend persisting CRDT/OT edit operations and serving live document snapshots during large company all-hands sessions.
Max p99
≤ 60 ms
Availability
≥ 99.5%
Budget
≤ $6,200
Functional Requirements
- FR-1POST /docs/{doc_id}/ops — Appends ordered edit operation and broadcasts to active collaborators.
- FR-2GET /docs/{doc_id}/state — Loads latest compacted document snapshot + trailing op log.
- FR-3PATCH & DELETE /docs/{doc_id}/ops — Updates, cancels, or deletes doc_id records and immediately invalidates or updates cached state (read-after-write).
- FR-4Reconnecting collaborators must see all acknowledged edits immediately (read-after-write) despite storage brownouts.
Workload Profile
Baseline Editing48,000 Read RPS / 13,000 Op Write RPS
All-Hands Doc Surge135,000 Read RPS / 36,000 Op Write RPS
Active Working Set24 GB active document state & op buffers
Fault Scenario7x storage gray-latency spike in Wave 3
Consistency Model
Read-after-write operation visibility required per doc_id; circuit-breaker / write buffering needed for brownout survival.
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