Thomas Camlong
fee2e6a6af
Four commits now apply the off-screen row treatment; only the first was A/B'd. Records
which is which, and warns how to read a result for the three widgets that do not overdraw
on the test backup - a measurement there will correctly show no change, because the benefit
only exists once an integration returns more rows than the tile can show.
Also records two things that look like gaps and are not:
- content-visibility was applied to five of the 26 ScrollArea widgets on purpose. It
costs containment work and can be wrong on self-measuring content such as charts and
the notebook, so the rule was: apply where list length is decided by remote data.
- React cache() is server-only. It already wraps getBoardByNameAsync, getHomeBoardAsync,
getRscServerSettingsAsync and getQueryClient; it does nothing for client widget
rendering, where react-query does the caching and its gcTime was already verified at
5 minutes rather than the 24 hours the original fix catalogue assumed.
126 lines
7.0 KiB
Markdown
126 lines
7.0 KiB
Markdown
# Where this left off, and what to do next
|
||
|
||
Written as a handoff. The branch is green and everything below is measured except where explicitly
|
||
marked.
|
||
|
||
## 1. Verify the unmeasured changes
|
||
|
||
Four commits apply the off-screen-row treatment beyond the one widget where it was measured. All are
|
||
typechecked and lint-clean, none are A/B'd — they are the only performance claims on this branch not
|
||
verified before commit.
|
||
|
||
| commit | widget | measured on this board? |
|
||
| --- | --- | --- |
|
||
| `7550766f6` | mediaReleases | **yes** — 135 → 55 image requests, 8346 → 5117 layout objects |
|
||
| `c526dd2b7` | mediaRequests-requestList | no — but overdraw confirmed: 1,512 px of cards in a 405 px tile, 60 images |
|
||
| `040f10594` | rssFeed, notifications, calendar event list | no — these do **not** overdraw on this board |
|
||
|
||
The last row needs care when reading a result. On the test backup rssFeed renders 7 nodes and the
|
||
calendar's 7 rows fit their tile, so a measurement will correctly show **no change**. That is not a
|
||
failure of the change — the benefit only exists for a user whose integrations return more rows than
|
||
the tile can show. To observe it, use a backup with a busier feed, or shrink the tile.
|
||
|
||
For `c526dd2b7`, which does overdraw here, a real effect is expected:
|
||
|
||
```bash
|
||
# restore two containers on identical data, one per image, then:
|
||
STRESS_BASE_URL=http://127.0.0.1:PORT STRESS_BOARD=default \
|
||
node --experimental-strip-types scripts/benchmarks/measure-board-paint.mts
|
||
```
|
||
|
||
Expect **image requests to fall**. Do **not** expect JS heap to move: decoded bitmaps live outside
|
||
`JSHeapUsedSize`. Three repeats per side — a single run wrongly suggested a −16% heap win on the first
|
||
widget. If image requests do not fall, revert it.
|
||
|
||
## 1b. What was deliberately not changed
|
||
|
||
26 widgets use `ScrollArea`; the treatment was applied to five. `content-visibility` is not free — it
|
||
costs containment work, and on content that measures itself (charts, editors, the notebook) skipping
|
||
layout can be actively wrong. The rule used: apply it where list length is decided by remote data,
|
||
leave fixed-size and chart widgets alone.
|
||
|
||
`beszelSystemStats`, `beszelSystemTable` and `beszelSystemGrid` report large row counts in the
|
||
overdraw tool, but that is the tool misreading SVG groups as rows — their content fits their tiles.
|
||
|
||
## React `cache()` and memoisation — already in place
|
||
|
||
Recorded because it looks like a gap and is not.
|
||
|
||
React `cache()` is **server-only**: it dedupes within a single RSC render and does nothing for client
|
||
widget rendering. It is already applied where it belongs — `getBoardByNameAsync`, `getHomeBoardAsync`,
|
||
`getRscServerSettingsAsync` and `getQueryClient` are all wrapped, the last with a comment explaining
|
||
the dedup.
|
||
|
||
Client-side data is cached by tRPC/react-query, whose `gcTime` was already checked and found to be
|
||
5 minutes, not the 24 hours the original fix catalogue assumed. `React.memo` is already used in the
|
||
clock, calendar and releases widgets.
|
||
|
||
## 2. The one lever with real headroom left
|
||
|
||
**The tRPC router imports every integration eagerly.** A single **16.10 MiB subtree of 460 files** is
|
||
reached by every API route, and because Next preloads route bundles it is resident before the first
|
||
request. This pays twice:
|
||
|
||
- ~41 MiB of retained bundle source (28% of the live server heap) — V8 keeps a script's source alive
|
||
while any function in it may still be lazily compiled
|
||
- ~38 MiB of V8 compiler zone memory, which is **proportional to how much JavaScript V8 compiles** and
|
||
is not reachable by any V8 flag (`--max-opt` is a null result; only `--jitless` removes it, and that
|
||
breaks rendering)
|
||
|
||
Nothing else has this profile. Every allocator and V8-level avenue is closed — see
|
||
[REJECTED.md](./REJECTED.md).
|
||
|
||
Start from `analyze-require-graph.mjs`, which found the shared subtree, and
|
||
`[root-of-the-server]__0g06wx7._.js` as the chunk reaching 460 files.
|
||
|
||
## 3. Known-good but deliberately deferred
|
||
|
||
| item | prize | why it was not done |
|
||
| --- | --- | --- |
|
||
| ASCII-escape server bundles | **9.45 MiB** | Proven mechanism — 2.00 vs 1.00 bytes/char; one char above U+00FF doubles a whole source string. Needs a build-time rewrite of minified **vendor** output, so it deserves its own PR and safety argument |
|
||
| Lazy `mysql2` / `pg` | 21.4 MiB | Three implementations, all broken; see REJECTED.md. Structurally blocked because `createDb` must stay synchronous |
|
||
| `beszelSystemStats` at 1,156 nodes | unknown | Second-heaviest widget, but its cost is chart SVG (`<g>×317`), so reducing it changes what is drawn |
|
||
| `documents` reads 18–32 | unknown | Never investigated; each document carries overhead |
|
||
|
||
## 4. For the clean PR
|
||
|
||
The instruction was to close this experimental PR and open one with only the verified fixes, judged on
|
||
lines-of-code to performance ratio. On the evidence, that set is:
|
||
|
||
| change | size | measured effect |
|
||
| --- | --- | --- |
|
||
| `--max-semi-space-size=4` | **1 line** | −19% idle, −21% peak |
|
||
| `preloadEntriesOnStart: false` | **1 line** | −52% anon at idle; 310 fewer files even at full load |
|
||
| Umami: stop fetching 100k raw events per refresh | 1 file | −26% peak, −93% transient buffers, largest allocation 46.4 → 2.4 MiB |
|
||
| `serverExternalPackages` (mysql2/pg + 8 more) | 1 block | −21 MiB idle |
|
||
| `content-visibility` on media-release cards | 4 lines | −59% image requests, −41% layout objects |
|
||
| ssh2 WASM heap (docker-modem patch) | 1 patch | −15 to −18 MiB external at every stage |
|
||
|
||
Together these produce the headline: **−26% peak anon, −52% at idle**, no overlapping ranges at any
|
||
stage, for **+18% CPU**.
|
||
|
||
Two things to leave out or flag:
|
||
|
||
- **The gRPC patch** removes 112 files and 6 MiB from an isolated `require`, but is **not separately
|
||
visible in a full run**. Bundle hygiene, not a measured memory win.
|
||
- **Median board load reads +30%** but is **not established** — individual loads were
|
||
[506, 383, 1233] and [848, 431, 574] before against [780, 808, 515] and [621, 579, 1004] after,
|
||
heavily overlapping with no cold-then-warm pattern. If the latency trade matters, measure it properly
|
||
with many more samples; the suspicion is that it is real and concentrated in
|
||
`preloadEntriesOnStart`.
|
||
|
||
## 5. Read this before measuring anything
|
||
|
||
[METHODOLOGY.md](./METHODOLOGY.md). Every wrong number in this investigation came from an instrument,
|
||
not the application, and several were published before being caught. The short version:
|
||
|
||
- a heap snapshot **cannot** explain a peak — V8 GCs first and reports survivors only
|
||
- V8 truncates snapshot string contents to ~1 KiB
|
||
- snapshot objects are **not** live native handles
|
||
- measuring without a forced GC measures V8's growth, not a module's cost
|
||
- taking a CDP heap snapshot added **134 MiB to the process being measured**
|
||
- React per-component attribution silently returns **nothing** on a production build
|
||
- a fixed port can measure a **leftover container**
|
||
- **when a server-side change moves a client-side metric, the workload changed** — this is how
|
||
`--jitless` was caught faking a 24% win by under-rendering the page
|