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Jittery scrolling through unread posts #228

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opened 2026-10-21 19:04:37 +00:00 by littlefox · 2 comments

littlefox commented

2026-10-21 19:04:37 +00:00

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Reported by the user (D-057): scrolling quickly through unread posts jitters. The user suspects marking posts read makes the UI wait for something.

What the code does today (#180):

SEEN_JS in app/src/main_view/mod.rs runs every 250 ms. It calls getBoundingClientRect on every unread card, which forces layout while you scroll.
Each card seen goes to Rust. Rust awaits kom.mark_read (a server round trip), then bumps tick.
Bumping tick reloads and re-renders the whole thread (see the redraw issue). That probably causes the jitter more than the round trip itself does.
JUST_SEEN is written for every card, which also re-renders the thread.

Directions:

Use an IntersectionObserver instead of polling layout.
Batch the marks, and mark the cards read locally right away, sending to the server in the background.
Let a mark not reload the thread.

Done when: scrolling quickly through a few hundred unread cards has no long tasks (the measuring spec) and looks smooth on desktop and phone.

Reported by the user (D-057): scrolling quickly through unread posts jitters. The user suspects marking posts read makes the UI wait for something. What the code does today (#180): - `SEEN_JS` in `app/src/main_view/mod.rs` runs every 250 ms. It calls `getBoundingClientRect` on every unread card, which forces layout while you scroll. - Each card seen goes to Rust. Rust awaits `kom.mark_read` (a server round trip), then bumps `tick`. - Bumping `tick` reloads and re-renders the whole thread (see the redraw issue). That probably causes the jitter more than the round trip itself does. - `JUST_SEEN` is written for every card, which also re-renders the thread. Directions: - Use an `IntersectionObserver` instead of polling layout. - Batch the marks, and mark the cards read locally right away, sending to the server in the background. - Let a mark not reload the thread. Done when: scrolling quickly through a few hundred unread cards has no long tasks (the measuring spec) and looks smooth on desktop and phone.

littlefox added this to the 0.6: Performance milestone

2026-10-21 19:04:37 +00:00

littlefox added the

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area/reading

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2026-10-21 19:04:37 +00:00

littlefox referenced this issue

2026-10-21 19:08:08 +00:00

Local search index: up to ~80 MB in memory, and rewritten on every post once full #232

littlefox referenced this issue

2026-10-21 19:08:09 +00:00

Idle cost: timers and global signals that redraw while nothing happens #233

littlefox referenced this issue

2026-10-21 19:08:24 +00:00

Fewer server round trips when showing posts and threads #234

littlefox commented

2026-10-21 19:08:41 +00:00

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More from the codebase review (#230):

SEEN_JS runs every 250 ms even when nothing scrolls (#233).
Each mark is its own mark-as-read call; batching them is in #234.
Each mark also writes JUST_SEEN and bumps tick, both of which redraw the thread (#226).

More from the codebase review (#230): - `SEEN_JS` runs every 250 ms even when nothing scrolls (#233). - Each mark is its own `mark-as-read` call; batching them is in #234. - Each mark also writes `JUST_SEEN` and bumps `tick`, both of which redraw the thread (#226).

littlefox referenced this issue

2026-10-21 19:08:42 +00:00

Performance review of the whole codebase #230

littlefox referenced this issue

2026-10-21 19:53:27 +00:00

Reading view redraws everything, and every post read reloads the whole thread #226

littlefox referenced this issue from a commit

2026-10-21 22:59:05 +00:00

Perf: a scenario for reading cards by scrolling past them

littlefox referenced this issue from a pull request that will close it,

2026-10-21 23:11:07 +00:00

Read by being seen without reloading the thread; redraw only what changed #254

littlefox closed this issue

2026-10-22 00:53:34 +00:00

littlefox referenced this issue from a commit

2026-10-22 00:53:34 +00:00

Read by being seen without reloading the thread; redraw only what changed

littlefox commented

2026-10-22 01:50:34 +00:00

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Merged in #254; main run #426 green. Verified: full e2e suite on three profiles (327 passed) and tools/perf.sh against the baseline. Reading 120 cards by scrolling past them: server calls 287 → 99, layouts 119 → 35, style recalcs 126 → 61, main-thread time 1.2 → 0.37 s. Reading 300 posts along the chain: style recalcs −33 %. Idle main-thread time 0.03 → 0.01 s per 20 s.

Merged in #254; main run #426 green. Verified: full e2e suite on three profiles (327 passed) and `tools/perf.sh` against the baseline. Reading 120 cards by scrolling past them: server calls 287 → 99, layouts 119 → 35, style recalcs 126 → 61, main-thread time 1.2 → 0.37 s. Reading 300 posts along the chain: style recalcs −33 %. Idle main-thread time 0.03 → 0.01 s per 20 s.

littlefox referenced this issue

2026-10-22 02:01:20 +00:00

Fewer round trips: light previews, cached names, cards a few at a time #261

littlefox referenced this issue

2026-10-24 01:54:11 +00:00

Flaky: a post's menu loses its buttons now and then (calm-post, aux specs) #324