This fixes both of this and all the test are actually green. However I'm not convinced this is the right fix because it's a bit greedy: the problem is the following.

a derived of a derived returns a component
that component is read by the component function (and is marked as CLEAN)
mounting that component update a value of that triggers the original derived
this triggers the derived of derived which is marked asMAYBE_DIRTY
since that derived was already read it's not read again so it staysMAYBE_DIRTY
when the value changes the original derived is updated but since the derived of derived isMAYBE_DIRTY his reactions are not marked/scheduled

Now includingMAYBE_DIRTY in the flags to mark/schedule fixes it but i think it will schedule more than necessary and i don't know if this could have performance issues. The best action would be to mark the derived as clean if we can somehow detect that it was marked after being read but it's a bit of a weird situation (becuase if you, for example, read it again in an effect the bug it's not present)

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fix: mark reactions ofMAYBE_DIRTY reactions too

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changeset-botbot commentedJun 8, 2025•
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github-actionsbot commentedJun 8, 2025

Playground

pnpm add https://pkg.pr.new/svelte@16110

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dummdidumm commentedJun 8, 2025

Looking at the benchmark the overall time spent with GC has more than doubled, so as you say this is likely not the right fix (also because what would even be the difference between maybe dirty and dirty now?)

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paoloricciuti commentedJun 8, 2025•
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Yeah to be fair I was even surprised no test failed but I guess it's just removing an optimization.

I guess the right fix would be to find a way to set back this kind ofMAYBE_DIRTY toCLEAN even if it's not executed again.

Mmm...I guess technically the derived should be executed again since the value might change 🤔

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paoloricciuti commentedJun 8, 2025

Ok i tried a bit more, it's getting late: so I think the actual problem is that when we mark the reactions of the derived of derived the first time it's reactions are not yet populated because we are within the function call inupdate_reaction...so basically we update the block effect in thecomponent function, that invalidate the derived through the$effect.pre which should mark theblock for a rerun but it doesn't becauseblock is not going to be added as a reaction until the function finishes to run.

Still need to find a proper solution.

fix:set_untracked_writes forBLOCK_EFFECT's too

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paoloricciuti commentedJun 9, 2025

Ok this is a different fix: it's basically extending the logic for untracked writes toBLOCK_EFFECT's too (since theget_component function runs there...not sure of the performance implication, let's see what the benchmark say.

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paoloricciuti commentedJun 9, 2025

@dummdidumm looking at the benchmarks on main i seegc_time fluctuate a bit (i've seen times up to 400)...this branch currently shows 487 which is worse but not terribly worse maybe?

I wonder if this could be the fix.

paoloricciuti changed the title~~fix: mark reactions ofMAYBE_DIRTY reactions too~~fix: update untracked writes forBLOCK_EFFECTs too

Jun 9, 2025

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Jun 9, 2025

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chore: changeset

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paoloricciuti commentedJun 9, 2025•
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Tbf they seems pretty similar runningcompare

sbench_create_signals  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   403.54ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 438.36ms  gc_time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼    178.47ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 206.05mssbench_create_0to1  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  4.50ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 4.74mssbench_create_1to1  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  20.19ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 20.77ms  gc_time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   2.29ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.48mssbench_create_2to1  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  17.34ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 18.36ms  gc_time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   2.18ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.40mssbench_create_4to1  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  16.63ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 17.17ms  gc_time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼    2.12ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.46mssbench_create_1000to1  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 15.27ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 15.23ms  gc_time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.34ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   2.15mssbench_create_1to2  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  9.51ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 10.05ms  gc_time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  0.50ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.54mssbench_create_1to4  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   7.69ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 8.48ms  gc_time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼    0.43ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.50mssbench_create_1to8  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   6.35ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 6.96mssbench_create_1to1000  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  5.02ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 5.28mskairo_avoidable_owned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 273.14ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 271.49ms  gc_time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 5.73ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  5.39mskairo_avoidable_unowned  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 364.04ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 367.89ms  gc_time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 5.67ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 5.66mskairo_broad_owned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 407.80ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 405.03mskairo_broad_unowned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 407.99ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 407.22mskairo_deep_owned  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 180.61ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 182.64mskairo_deep_unowned  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 888.63ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 891.04mskairo_diamond_owned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 302.86ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   274.38ms  gc_time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 3.44ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   3.15mskairo_diamond_unowned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 384.47ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 383.55ms  gc_time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 3.65ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   3.21mskairo_triangle_owned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 101.15ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   89.68ms  gc_time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.51ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼    0.44mskairo_triangle_unowned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 209.01ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 207.17ms  gc_time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼    0.52ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.60mskairo_mux_owned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 307.59ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 306.99ms  gc_time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  1.85ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 1.96mskairo_mux_unowned  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 460.08ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 462.24ms  gc_time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  2.03ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 2.19mskairo_repeated_owned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 44.79ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 44.09ms  gc_time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.19ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   0.17mskairo_repeated_unowned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 45.48ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 44.72ms  gc_time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.18ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  0.17mskairo_unstable_owned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 76.36ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  74.33ms  gc_time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.64ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼     0.52mskairo_unstable_unowned  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 92.72ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 92.87ms  gc_time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼      0.61ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.82msmol_bench_owned  time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 232.39ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 230.48ms  gc_time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼  0.22ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.23msmol_bench_unowned  time: fastest is a (derived-reactions-maybe-dirty-marked)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 246.80ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 247.90ms  gc_time: fastest is b (main)    a: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼ 0.25ms    b: ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼   0.22ms