board

board (stress) — tanstack-do-db-collection example

A high-volume "task board" on one Durable Object — the at-scale stress test for on-demand windowed pagination. One board holds 5,000 tasks, but a client loads only a bounded window (top 50 by updated_at) and pages older ones in on demand via the cursor fetch.

Tasks are ordered by a mutable key: voting (▲) or starring (★) sets updated_at = now, which bumps a task to the top. That exercises move-in / move-out — a bump to a task a client never loaded arrives as an update delta for an absent key and upserts into the window (the always-emit rule, ADR-0002 C4). Uses useLiveInfiniteQuery, whose setWindow drives the real cursor loadSubset.

Run

npm install
npm run dev            # builds the client, then `wrangler dev`

Open http://localhost:8787 — the first load auto-seeds 5,000 tasks. Then:

• Bounded load. On join, loaded ≈ 51 (one peek-ahead row) even though total is 5,000 — the whole board is not synced.
• Scroll-back. Scroll the list (or "load older") to page older tasks via the cursor; window and loaded grow a page at a time.
• Bump / move-in. ▲ or ★ a task — it jumps to the top. Open a second tab and start the firehose: it bumps random (mostly cold) tasks server-side, and the other tab sees them move into its window.

Watch the deferred limitation, made visible

Under the firehose, loaded climbs past window: every cold task that gets bumped upserts into the collection and is never evicted, while the visible window stays 50. That growing gap is the deferred "bounded-window maintenance under churn" limitation (ADR-0001) — the example surfaces it as a number rather than hiding it. The window stays correct throughout; only the loaded set grows.

Shape

• src/worker.ts — BoardDO (one tasks collection; insert/update/delete mutations) + endpoints: GET /seed?n= (tie-bursts: every 25 tasks share an updated_at, so scroll-back crosses real tie boundaries), GET /bump?n= (the server-side firehose — mutates random tasks and broadcasts), GET /count.
• src/client.tsx — an on-demand collection with a range index (BTreeIndex) on the order column so the window pages lazily; a useLiveInfiniteQuery window; vote / star / delete; firehose toggle; the window / loaded / total metrics.