# language: Cache buffer syntax highlighting per row chunk \(\#63145\) · gitcafe/zed

[View on GitCafe](https://git.cafe/gitcafe/zed/commit/d7f28899166cead457a2239ad23056d0a980bd7c)

Repository: [gitcafe/zed](https://git.cafe/gitcafe/zed)

Visibility: public

Requested revision: d7f28899166cead457a2239ad23056d0a980bd7c

Requested commit: d7f28899166cead457a2239ad23056d0a980bd7c

Commit: d7f28899166cead457a2239ad23056d0a980bd7c

Tree: d84538c17942be0c958de4053dda37e7435bfdc3

Author: Kirill Bulatov

Committer: GitHub

## Message

````
language: Cache buffer syntax highlighting per row chunk (#63145)

Closes https://github.com/zed-industries/zed/issues/63730
Related to #52340 and #43460
Based on https://github.com/zed-industries/zed/pull/63138 and needs it
to be merged first.

`BufferSnapshot::chunks` re-ran the tree-sitter highlight query over the
requested range on every call, so scrolling and cursor movement paid the
full query cost per frame.

Highlight runs are now computed once per 50-row chunk (the same
`RowChunks` that back bracket colorization), resolved against the
current `HighlightMap` at compute time, merged into `(Range<usize>,
HighlightId)` runs, and kept in a cost-budgeted per-buffer LRU (10MB).
Entries reuse the `ResolvedHighlights` representation from #63138: each
stores the grammars and maps it was resolved against and is served only
while every map is pointer-identical (`is_current`), so theme changes
and grammar reloads invalidate structurally, with no invalidation hooks
and no global state.
Edits and reparses drop the cache through the existing `TreeSitterData`
swap.
Chunks spanning more than 64KB bypass the cache and fall back to direct
querying, so files with giant lines behave as before.

## Benchmarks

`editor_render_highlighted` and `editor_render_highlighted_minimap`
benches (`cargo bench -p benchmarks --bench editor_render`) move the
cursor through a generated 10K-line Rust file with real tree-sitter
highlighting, with and without the minimap.
The benches are new in this PR, so the baseline is the same binary with
`ZED_DISABLE_HIGHLIGHT_CACHE=1`, which routes rendering through the
pre-existing direct-query path.

Run 1 — baseline, cache disabled:

```
editor_render_highlighted          time: [1.7164 ms 1.7377 ms 1.7604 ms]
editor_render_highlighted_minimap  time: [12.273 ms 12.407 ms 12.549 ms]
```

Run 2 — cache enabled:

```
editor_render_highlighted          time: [1.4572 ms 1.4597 ms 1.4627 ms]
                                   change: [-16.378% -14.944% -13.526%] (p = 0.00 < 0.05)
editor_render_highlighted_minimap  time: [9.2750 ms 9.3213 ms 9.3744 ms]
                                   change: [-25.800% -24.872% -23.930%] (p = 0.00 < 0.05)
```

Over the same runs, GPUI reports window draw mean 0.81 ms → 0.68 ms and
p99 1.06 ms → 0.76 ms without the minimap, and mean 5.14 ms → 4.12 ms,
p99 6.12 ms → 4.75 ms with it.
The relative deltas held across two independent sessions (-14.1…-14.9%
and -20.7…-24.9%), while absolute times drift a few percent with machine
state.

Release Notes:

- Improved editor rendering performance in syntax-highlighted files,
especially with the minimap enabled
````

## Parents

- [318c664ec3e0d516760366c9a4cb26e38c08da36](https://git.cafe/gitcafe/zed/commit/318c664ec3e0d516760366c9a4cb26e38c08da36?format=markdown)

[Source at this commit](https://git.cafe/gitcafe/zed/tree/d7f28899166cead457a2239ad23056d0a980bd7c?format=markdown)