Performance model

Clank uses compilation and fine-grained subscriptions instead of rerendering component trees. A component function runs once when mounted. Its TSX expressions become independent bindings that subscribe only to the signals they actually read.

#Update guarantees

There is no virtual DOM tree, component rerender, or full-list diff of child VNodes on a normal signal update.

#Compiler-created granularity

<article class={selected.value ? "selected" : ""}>
  <h2>{document.value.title}</h2>
  <p>{document.value.summary}</p>
</article>

This creates three subscriptions: one for class, one for the heading text, and one for the paragraph text. Changing summary does not execute the component, recreate the article, touch its class, or update the heading.

Event callbacks, ref, use, key, bind:*, and literal values are not wrapped in reactive effects.

#Keyed lists

<For each={todos.value} by="id" fallback={<p>No todos</p>}>
  {(todo) => (
    <TodoRow todo={todo} />
  )}
</For>

Keys must be unique within the list. A property key such as by="id" or (item) => item.id is recommended for immutable records. Clank gives every retained object row a stable proxy with lazily created property signals. Replacing { id: "a", done: false } with { id: "a", done: true } preserves the row and notifies todo.done bindings without invalidating bindings that only read todo.id or todo.title.

Without by, object identity is the key. Primitive values use value plus index and are intended for simple display lists.

#Batching

Signal writes are synchronous. A single write invalidates all dependent computed values before running effects, so an effect reached through several computed branches runs once with settled values. Wrap related writes in batch() so each dependent effect executes once after the final write. transaction() provides the same coalescing plus rollback on failure.

#Hosted request routing

Managed ingress reads a fresh routing snapshot for each request. Verified custom domains are loaded in one query for all deployed projects, and installations with only local applications skip provider fleet reads. Domain revocations, reassignments, process replacement, and provider generation checks remain live; routing does not wait for a cache timeout.

The platform regression suite counts domain queries across multiple deployed applications and checks immediate host reassignment and revocation alongside the rollout and provider tests.

#Measuring identity

The renderer regression suite asserts identity, not merely final HTML. It stores references to list elements and text nodes, edits and reorders immutable records, and verifies that the same objects remain mounted. This prevents a visually correct remount from being mistaken for a fine-grained update.

Run the performance invariants with:

npm test -- tests/dom.test.mjs

#CI performance budgets

npm run performance builds the framework and prints a JSON budget report. The same budget checks run in npm test and the complete release gate on both supported Node versions. Budgets fail CI for excess work or bytes, including missing or non-finite measurements:

The byte limits cover each compiled module separately, not its transitive imports or a complete application bundle. Compression uses gzip level 9. Wall-clock timings are reported for local comparison but do not fail CI on shared runners. The existing real ingress test separately enforces one domain query and zero fleet queries for a local-only installation.

Change a budget in scripts/performance-budgets.mjs only with a reviewed explanation of the additional work or payload. To reproduce ingress and HTTP transfer regressions alongside these budgets, run npm test -- tests/platform.test.mjs tests/node.test.mjs.

#Regression evidence

The performance pass covers reactive propagation, keyed DOM updates, SSR lifecycle, HTTP streaming and static transfer, database/query caching, authentication and jobs, and local/provider deployment paths. The fixes below use deterministic work counts and real HTTP/database tests; they are not claims about production throughput or latency under an unmeasured workload.

The regressions live in tests/core.test.mjs, tests/ssr.test.mjs, tests/node.test.mjs, and tests/platform.test.mjs. npm run check also verifies DOM identity, authentication/ownership, live synchronization, durable jobs, provider fencing, rollout health gates, migration failure, and rollback through the packaged-release conformance journey. CI runs the supported Node 22.16 and Node 24 versions. Reproduce timing measurements on the deployment workload before drawing capacity conclusions from these narrower invariants.

#Reproducible load and reliability profiles

The repository's scripts/load/README.md describes disposable HTTP A/B, authentication, managed ingress, live-connection, crash/replay, and large-list browser workloads. The generators create loopback servers and synthetic databases, record failed and dropped requests, and can compare a published package with a locally built revision. They do not target production.

The September 2026 load pass found two regressions: evicted live-query results lost their invalidation dependencies, and platform project visibility queries scanned unrelated tenants. Live subscriptions now retain dependency metadata independently of cached result payloads; project lists and dashboards use indexed ownership and membership lookups. The regression tests are tests/live-cache-eviction.test.mjs and tests/platform-tenant-lookups.test.mjs.

See the methodology and raw results for the tested limits. Request rates, account counts, open streams, and running application processes are different capacity measures. Repeat representative workloads on an isolated staging deployment with production-equivalent resources and external generators before setting launch capacity. Include password-login bursts, populated metric histories, and configured quotas.

Dashboard overviews aggregate only the current 24-hour metric summary in one query per project. They retain the detailed metrics endpoint's interval counts, minute peaks, request counts and latency histograms without building unused chart points or reading a discarded previous period. The detailed metrics view still includes those charts and comparisons.

#Complete application load budgets

clank workbench performance page.har budgets.json --baseline=before.har --json checks an actual browser navigation, including transitive modules, CSS, images, fonts, and other HTTP requests initiated through the page's load event. Export a HAR from a fresh browser context with cache disabled, after load completes. Use the same URL, fixture, viewport, and browser for the baseline and candidate. Disable service workers. HAR files can contain credentials: keep the raw captures private; the report excludes headers, cookies, bodies, URL credentials and queries. Resource paths remain visible, so use synthetic fixture URLs.

The budget file declares four nonnegative integer maxima:

{ "requests": 30, "bodyBytes": 300000, "javascriptBytes": 100000, "cssBytes": 30000 }

Body bytes are the HAR's encoded response body sizes, including compression actually served; they exclude HTTP headers. JavaScript and CSS are classified by response MIME type. Every request counts, including repeats and redirects. Query variants aggregate under the same origin/path. Resources and baseline byte deltas identify new, larger, and removed payloads. A script fetched indirectly counts exactly like a top-level script. This measures observed loading, not unused code or a static dependency graph; exercise lazy routes separately.

The command exits nonzero for exceeded budgets, unknown measurements, detected cache hits, failed responses, or a missing HTML document. Multiple-page captures require --page=<id>; the same ID selects both captures. Requests initiated after load are excluded, while requests started before load count in full. The capture must finish those responses before export. The report cannot detect requests omitted by the capture tool; keep network recording enabled throughout navigation. Add this command to an application's CI after its browser capture step.