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tiennm99 cdf2295ef6 docs(canvas): correct CF DO limits in resize doc and plan

Earlier docs assumed a 1 GB per-DO storage cap. Actual May 2026 free-tier
limits per the CF DO docs:
- 10 GB per Durable Object
- 5 GB per account (the real Free-tier ceiling)
- 2 MB per BLOB row
- 1,000 req/sec soft cap per DO

Practical effect: canvas can grow to ~70,000 × 70,000 on Free (was previously
documented as ~32K × 32K). Existing 64 KB CHUNK_BYTES is well-suited:
clustered writes (single pixels + image patches) minimize read-modify-write
amplification; bigger chunks would only help uniform-random writes which
isn't rplace's workload.

No code change. Just doc accuracy.

2026-05-10 00:07:39 +07:00

3.9 KiB

Raw Blame History

title, status, priority, created, phases, source, brainstorm, researchReports

title

status

priority

created

phases

source

brainstorm

researchReports

Migrate canvas storage from Upstash to Durable Object SQLite

in-progress

2026-05-09

brainstorm

../reports/brainstorm-260509-2309-canvas-on-do-storage.md

../reports/researcher-260509-2255-forever-free-hosting.md

../reports/researcher-260509-2246-vercel-migration-feasibility.md

Plan: Migrate canvas storage from Upstash → Durable Object SQLite

Goal

Eliminate Upstash Redis dependency. Move canvas (16 MB) and per-user cooldown state into the existing CanvasRoom Durable Object via its SQLite-backed storage. Keep $0/month forever, hobby-scale (50 concurrent / <1 placement/sec). Resize must be config-change-only.

Context

Brainstorm: plans/reports/brainstorm-260509-2309-canvas-on-do-storage.md (approved)
Storage research: plans/reports/researcher-260509-2255-forever-free-hosting.md
Migration feasibility: plans/reports/researcher-260509-2246-vercel-migration-feasibility.md

Architecture (locked)

Browser ──HTTP/WS──▶ Worker (Hono, thin proxy)
                          │
                          └─▶ CanvasRoom DO (idFromName('main'))
                                ├── canvas_chunks (SQLite BLOB rows × CHUNK_COUNT)
                                ├── cooldowns      (user_id → expires_at, lazy GC)
                                └── WebSocket hibernation hub (broadcast)

Constants drive resize: CHUNK_COUNT = ceil(CANVAS_WIDTH * CANVAS_HEIGHT / CHUNK_BYTES). Bump width/height → redeploy → DO lazy-inits missing chunks.

Phases

#	Phase	Status	Effort
1	Storage Foundation	completed	~3h
2	DO Integration & Worker Proxy	completed	~4h
3	One-Shot Upstash Migration	code-complete (awaits production run)	~2h
4	Cleanup & Dependency Removal	blocked (waits for Phase 3 prod migration + 7d)	~2h
5	Deploy & Documentation	partial (resize doc done; deploy + README await Phase 4)	~1h

Total estimate: ~12h (1.5 working days) Status: Phases 1, 2, 3 (code) and 5 (resize doc) complete. Phase 3 prod run + Phase 4 cleanup are user-gated.

Dependencies

Phase order is strict: 1 → 2 → 3 → 4 → 5. Each phase blocks the next.

Success Criteria

Zero @upstash/redis references in src/
package.json no longer depends on @upstash/redis or ioredis
wrangler dev runs locally without UPSTASH_REDIS_* env vars
Existing pixels preserved through migration (verify a known coordinate)
WS broadcast still functional end-to-end
All tests pass (npm run test:all)
Resize procedure documented in docs/
Production deploy verified with smoke test
$0 monthly bill confirmed after 7 days

Risk Register

Risk	Severity	Mitigation
Workers req/day at 87% of cap on peak day	Med	Keep `s-maxage=10` cache on `/api/canvas`; monitor via CF dashboard
Test rewrite scope creep	Low	Time-box testcontainers→DO test rewrite to 4h; cut e2e if needed
Migration corrupts canvas	High	Keep Upstash data 7 days post-migration as rollback
DO single-region latency regression	Low	Same as today's Upstash (single region) — no change
Storage exposure if canvas grows	Low	Per-DO 10 GB / per-account 5 GB on Free; current 16 MB has 300× headroom
BLOB row size cap (2 MB)	None	`CHUNK_BYTES = 64 KB` has 32× headroom from this limit
Per-DO 1,000 req/sec soft cap	None	Hobby load is ~1 req/sec; edge cache absorbs `/api/canvas`

Rollback Plan

Phases 1–4 are reversible until Phase 5 deploy. Keep Upstash creds and old code paths in git history for 30 days. If post-deploy issues, git revert + redeploy.

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