Memory leak after upgrading from 1.9.5 to 2.4.0

[noveogroup-amorgunov]

Hey. We encountered a memory leak problem on server (nextjs page router) after update redux-toolkit from 1.9.5 to 2.4.0. After investigating the heap snapshot, we found that the problem was in the reselect (describe in reduxjs/reselect#635).

A temporary fix is ​​to use this lruMemoize for createSelector instead of weakMapMemoize. But anyway I think this information should be described in the documentation (may be in migration guide) because this is clearly not expected behavior (I mean memory leak).

diagram after fallback to lruMemoize in 02/20:

[markerikson]

Can you give an example of the overall usage patterns that you have in the app? Store creation, frequency of actions, what you're selecting?

[phryneas]

We would still very much like a reproduction of the situation you are seeing, but specific to a combination of SSR, default states, and selectors with primitive arguments, this repro might help to investigate:
https://codesandbox.io/p/devbox/selectors-default-value-leak-c7g9rr

Core of that reproduction is:

  const slice = createSlice({
    name: "slice",
    initialState: {
      items: [],
    },
    reducers: {},
  });

  const selector1 = createSelector(
    [(fullState) => fullState.slice, (_, userId) => userId],
    (userState, userId) => ({ userId }),
    {
      memoize: weakMapMemoize,
      argsMemoize: weakMapMemoize,
    }
  );

  for (let i = 1; i <= 500; i++) {
    const store = configureStore({ reducer: { slice: slice.reducer } });
    selector1(store.getState(), i);
  }

The problem here being that the initial state of slice, { items: [] } never leaves memory and will be returned for every store created, even if then different primitive selector arguments are used beyond that.

For debugging, I ran this locally and added this line to reselect.mjs

function weakMapMemoize(func, options = {}) {
  let fnNode = createCacheNode();
+  (globalThis.rootNodes ??= []).push(fnNode)
  const { resultEqualityCheck } = options;

Then at the end of the IIFE

  console.log('finished', globalThis.rootNodes)
  debugger;