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ignore: add existence check for ignore files #1381

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ignore: add existence check for ignore files #1381

wants to merge 1 commit into from

Commits on Sep 17, 2019

  1. ignore: add existence check for ignore files 

    This commit adds a simple `.exists()` check for `.gitignore`,
`.ignore`, and other similar files before actually calling
`File::open(…)` in `GitIgnoreBuilder::add`.

The reason is that a simple existence check via `stat` can be faster
than actually trying to `open` the file, see
https://stackoverflow.com/a/12774387/704831. As we typically expect(?)
the number of directories *without* ignore files to be much larger
than the number of directories *with* ignore files, this leads to an
overall speedup.

The performance gain is not huge for `rg`, but can be quite significant
if more `.gitignore`-like files are added via
`add_custom_ignore_filename`. The speedup is *larger* for folders with
*low* files-per-directory ratios.

Benchmark results
-----------------

`rg --files` in my home folder (200k results, 6.5 files per directory):

| Command | Mean [ms] | Min [ms] | Max [ms] | Relative |
|:---|---:|---:|---:|---:|
| `./rg-master --files` | 396.4 ± 3.2 | 390.9 | 400.0 | 1.05 |
| `./rg-feature --files` | 376.0 ± 3.6 | 369.3 | 383.5 | 1.00 |

`rg --files --hidden` in my home folder (800k results, 5.4
files per directory)

| Command | Mean [s] | Min [s] | Max [s] | Relative |
|:---|---:|---:|---:|---:|
| `./rg-master --files --hidden` | 1.575 ± 0.012 | 1.560 | 1.597 | 1.06 |
| `./rg-feature --files --hidden` | 1.479 ± 0.011 | 1.464 | 1.496 | 1.00 |

`rg --files` in the chromium-79.0.3915.2 source tree (300k results, 12.7 files per
directory)

| Command | Mean [ms] | Min [ms] | Max [ms] | Relative |
|:---|---:|---:|---:|---:|
| `~/rg-master --files` | 445.2 ± 5.3 | 435.6 | 453.0 | 1.04 |
| `~/rg-feature --files` | 428.9 ± 7.0 | 418.2 | 440.0 | 1.00 |

`rg --files` in the linux-5.3 source tree (65k results, 15.1
files per directory)

| Command | Mean [ms] | Min [ms] | Max [ms] | Relative |
|:---|---:|---:|---:|---:|
| `./rg-master --files` | 94.5 ± 1.9 | 89.8 | 98.5 | 1.02 |
| `./rg-feature --files` | 92.6 ± 2.7 | 88.4 | 98.7 | 1.00 |
    @sharkdp
    sharkdp committed Sep 17, 2019
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