# Switcher performance — measured bottlenecks

Benchmark harness: `src/project/bench_switcher.cpp` (manual target `bench_switcher`,
not a ctest). Run:

```sh
cmake -S . -B build-rel -DCMAKE_BUILD_TYPE=Release
cmake --build build-rel --target bench_switcher
./build-rel/bin/bench_switcher <project-root> /tmp/switcher_metrics.txt
```

Reference project: `~/prj/r7.20/mobydick` — **12,234 files**, **17,184 ctags
symbols**, 6.3 GB tree.

## One-time cost when the switcher opens (UI thread, synchronous)

| Stage                      | Release | Debug (shipped) |
|----------------------------|--------:|----------------:|
| `ProjectIndex::listFiles`  |  ~84 ms |          ~78 ms |
| `SymbolIndex::listSymbols` | ~974 ms |         ~499 ms |
| build items + `setItems`   |   ~5 ms |        ~45-70 ms |

- `listFiles` is a `git ls-files` subprocess — acceptable but blocks the UI.
- `listSymbols` is a **ctags subprocess (~0.5-1 s)** — the dominant open-cost,
  and it blocks the UI thread. (Cost is in the external binary, not our parse.)

## Per-keystroke cost — the interactive bottleneck

`PaletteModel::setQuery` → re-rank. Originally O(N) every keystroke; the cost
*grew* with query length even as the result set shrank.

Full-scan (every keystroke re-scores all N), Release:

| Query            | files    | symbols  |
|------------------|---------:|---------:|
| `server`         |  ~14 ms  |  ~30 ms  |
| `src server go`  |  ~17 ms  |  ~36 ms  |

Debug (what ships): **270-342 ms (files)**, **459-598 ms (symbols)** per
keystroke — unusable.

## Fix 1 — incremental narrowing (done)

When a query only **appends** to the previous one, re-score only the currently
visible subset (the match set is monotonic under lengthening/adding a needle),
turning later keystrokes from O(N) into O(previous matches). Exactness is
guarded by `test_palettemodel::incrementalMatchesFullScan` (incremental ==
full-scan, incl. the typo tier).

Effect once the set narrows (Release, type-forward):

| Query    | full-scan | incremental |
|----------|----------:|------------:|
| files `server`   | ~14 ms | **~6.6 ms** |
| symbols `server` | ~30 ms | **~9.0 ms** |

Early keystrokes (`s`, `se`) remain full-N because almost everything matches —
correct and unavoidable without a prefix index.

## Fix 2 — build the installed plugin optimized (recommended)

The shipped `olliepalette.so` is a **Debug** build (`-g`, no `-O`). Release is
~5-8× faster on every hot path above. Install a `Release` or `RelWithDebInfo`
build.

## Follow-up — move indexing off the UI thread (done)

`ProjectIndexer` (`src/project/projectindexer.{h,cpp}`, in `project_lib`, 6
tests) runs `listFiles` / `listSymbols` on the thread pool (`QtConcurrent` +
`QFutureWatcher`) and delivers results on the UI thread via `filesReady` /
`symbolsReady`, caching per project root. The switchers now:

- open the palette **immediately** (cache hit → instant; miss → a transient
  "Indexing…" / "Indexing symbols…" placeholder), and
- repopulate via the ready signal when the background job finishes.

A per-root generation counter drops superseded/invalidated results. The cache
is dropped on `KateProjectBridge::projectChanged` so a project switch re-indexes.
Net effect: the UI thread never blocks on git/ctags; the ~1 s Alt+G stall is
gone (first open shows a placeholder and fills in; subsequent opens are instant
from cache).