[query-core] [performances] `setQueryData` dispatches a `success` event (and triggers broadcast/persist) even when the new data is structurally identical to the cached data

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@praveen-kumary 已经在做这个了。

开始于 2026年10月30日。

  • #12462 来自 @praveen-kumary —— 未关闭

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调研方向

Start by reading setData and replaceData in the query core, then trace how setQueryData and setQueriesData call them. Check the tests covering manual cache writes, cache events, and explicit updatedAt values. Done means structurally identical manual writes can skip success events while explicit timestamp updates and fetch writes retain their intended behavior.

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描述

Describe the bug

queryClient.setQueryData always writes the new data through Query#setData, which dispatches a success cache event, increments state.dataUpdateCount and refreshes timestamps — even when the new data is structurally identical to what is already cached.

Since v5, setData already runs a deep comparison on every write for structural sharing (replaceData), so the equality is already computed — but it is only used to preserve references, not to skip the write.

Minimal repro (no framework needed, @tanstack/query-core 5.105.0):

import { QueryClient } from '@tanstack/query-core';

const client = new QueryClient();

let events = 0;
client.getQueryCache().subscribe((cacheEvent) => {
  if (cacheEvent.type === 'event' && cacheEvent.event.type === 'success') events++;
});

const base = { id: '1', name: 'item', meta: { tag: 'a', n: 1 } };

client.setQueryData(['item', '1'], base);

// Same content, new reference — the typical upsert pattern used by cache-sync helpers:
for (let i = 0; i < 10; i++) {
  client.setQueryData(['item', '1'], (old) => ({ ...old, ...JSON.parse(JSON.stringify(base)) }));
}

console.log(events);                            // 11 — ten extra 'success' events for data that never changed
console.log(client.getQueryCache().find({ queryKey: ['item', '1'] })!.state.dataUpdateCount); // 11

Expected: a manual write whose result is structurally identical to the current data should not dispatch a cache event (or at least should be able to).

Why it matters

The no-op write is invisible to components — because the structural-sharing result is referentially identical to the old data, observers do not re-render — so the cost never shows up as a visible bug. But every dispatched success event is still fully processed by:

  • @tanstack/query-broadcast-client-experimental — on every success event it structured-clones the query's full state and posts it on the channel.
  • @tanstack/query-persist-client-core with manual persistQueryByKey (the pattern recommended for manual cache updates, see #6310) — every call writes the full state to storage, and an IndexedDB put structured-clones its value synchronously on the main thread.

So an application that upserts a parent entity plus its N children into the cache per page transition (a common normalized-cache pattern) pays N state clones + N cross-tab posts per transition even when nothing changed.

Measured in an application with that pattern (one page transition entering an edit form that upserts ~10 cached entities, warm cache):

no guard no-op skip
success events dispatched 609 193
full-state writes to IndexedDB 218 16

The 416 / 202 eliminated operations were all structurally no-op writes. (We currently work around this at the application level with a deep-equality pre-check in a setQueryData wrapper plus a persistQueryByKey dedup keyed on dataUpdateCount; an in-library fix would cover all call sites at once.)

Suggested fix

setData already computes the shared result, and when the whole tree is structurally identical, replaceData returns the previous reference itself — so the short-circuit is a zero-cost reference comparison:

setData(newData, options) {
    const data = replaceData(this.state.data, newData, this.options);
    if (options?.manual && data === this.state.data) return data; // no-op manual write: skip the dispatch
    this.#dispatch({ data, type: 'success', dataUpdatedAt: options?.updatedAt, manual: options?.manual });
    return data;
}

Scoping to manual: true (writes from setQueryData / setQueriesData) leaves the fetch path untouched.

Behavior change to flag

  • dataUpdatedAt / dataUpdateCount would not bump on a skipped no-op write. For manual writes this seems correct (nothing was updated), but it is an observable change.
  • A call that passes an explicit updatedAt option should probably still dispatch, since the caller explicitly asked for a timestamp change.

Versions

"@tanstack/eslint-plugin-query": "5.105.0",
"@tanstack/query-broadcast-client-experimental": "5.105.0",
"@tanstack/query-persist-client-core": "5.105.0",
"@tanstack/svelte-query": "6.3.6",
"@tanstack/svelte-query-devtools": "6.3.6",
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  4. 提交 Pull Request，并在描述里引用这个 Issue 编号。

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