Coalesce position rendering without dropping dispatch events
A replay of 500 vans updating twice a second freezes the browser. Dropping every other message improved drawing but also lost assignment changes.
- Focused work estimate
- 3h 30m + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Backpressure · Rendering performance · Event classification
Estimated field mix
- Performance engineering50%
- Real-time systems30%
- Frontend20%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
The fictional Cedar delivery depot dispatches vans through a browser map and accessible list. Synthetic telemetry arrives through a gateway with device sequence numbers. This is operational fleet software practice; no real driver tracking, employee scoring, or routing safety guarantee is part of the project.
Setup prerequisites
- Synthetic vehicle telemetry with device sessions and sequence numbers
- Dispatch assignment and authorized region API contracts
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
- FLEET-101 · Keep invalid coordinates from appearing as real vans
- FLEET-102 · Show dispatchers how old each vehicle position is
- FLEET-104 · Prevent delayed telemetry from moving a van backwards
- FLEET-103 · Fit selected vehicles without zooming out across the entire planet
- FLEET-105 · Reconnect the map without losing updates between snapshot and stream
- FLEET-106 · Resolve competing dispatch assignments explicitly
- FLEET-107 · Keep map, list, and counts on the same filtered vehicle set
- FLEET-108 · Remove out-of-region location data when dispatch scope changes
Acceptance criteria
- Position drawing may coalesce to the newest accepted fix per vehicle within a bounded frame window.
- Assignment, authorization, and removal events follow their full ordered state path and are never discarded as visual updates.
- A reproducible load profile records input rate, render frequency, memory bound, and keyboard interaction latency.
Implementation constraints
- Separate authoritative state reduction from rendering cadence; use synthetic bounded traces.
Verification to include
- Replay the agreed 500-vehicle trace and measure the documented interaction budget.
- Interleave assignment, region removal, and position bursts; all nonvisual state transitions apply and removed vehicles do not reappear.
Deliverables
- Render coalescing scheduler and mixed-event load report
Rollout and recovery
Canary with conservative draw limits; reduce displayed live density or use the list if interaction budgets fail, preserving command state.
Value of the work
For the engineer: Practice geospatial boundaries, stream ordering, snapshot recovery, and concurrent operational commands.
For the team: Inspect whether a developer keeps dispatch decisions grounded in current authorized data and exposes uncertainty during outages.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.