Performance notes: measurements on Earth before and after the render and history caches 8d194f035eb6

# Performance notes

## 2026-09-28: render and history caches (hub spec §16.3)

Earth, OxygenHub on its own disk, median of seven requests per page with

`curl`, the `oxygen` repository (about 900 changes). File pages were the

slow ones; the raw bytes of the same files took 5 ms, so the time was in

rendering and in history, not in reading the state.

| Page | Before | Render caches | + last change and blame | 

|---|---:|---:|---:|

| `oxygen/file/main/docs/spec.md` (129 KB of Markdown) | 196 ms | 192 ms | 8 ms |

| `oxygen/file/main/crates/oxy-core/src/repo/mod.rs` | 400 ms | 205 ms | 18 ms |

| `oxygen/file/main/crates/oxy-core/src/state.rs` (962 lines) | 317 ms | 196 ms | 14 ms |

| `…/state.rs?blame=1` | 428 ms | 303 ms | 23 ms |

| `oxygen` overview | 8 ms | 7 ms | 7 ms |

| `oxygen/changes/main` | 26 ms | 27 ms | 27 ms |

What was cached, all in memory, bounded, least recently used first:

- Rendered Markdown by the text and its two link bases (32 MiB).

- Highlighted files by file name and text (64 MiB).

- A file's last change by state and path (4 MiB): it was found with

  `log_for_path_in`, which rebuilt the whole state and read every change on

  each view. It is the biggest single win.

- Blame by state and path (64 MiB).

A state is content addressed, so none of these can go stale; what can

change (bookmark and tag labels on a change) is still worked out on every

view. The first view of a file still pays the full cost once.

`?plain=1` downloads no longer compute the last change or the sidebar.