Andrew Gallant 46fb77c20c
searcher: bump buffer size
This increases the initial buffer size from 8KB to 64KB. This actually
leads to a reasonably noticeable improvement in at least one work-load,
and is unlikely to regress in any other case. Also, since Rust programs
(at least on Linux) seem to always use a minimum of 6-8MB of memory,
adding an extra 56KB is negligible.

Before:

    $ hyperfine -i "rg 'zqzqzqzq' OpenSubtitles2018.raw.en --no-mmap"
    Benchmark #1: rg 'zqzqzqzq' OpenSubtitles2018.raw.en --no-mmap
      Time (mean ± σ):      2.109 s ±  0.012 s    [User: 565.5 ms, System: 1541.6 ms]
      Range (min … max):    2.094 s …  2.128 s    10 runs

After:

    $ hyperfine -i "rg 'zqzqzqzq' OpenSubtitles2018.raw.en --no-mmap"
    Benchmark #1: rg 'zqzqzqzq' OpenSubtitles2018.raw.en --no-mmap
      Time (mean ± σ):      1.802 s ±  0.006 s    [User: 462.3 ms, System: 1337.9 ms]
      Range (min … max):    1.795 s …  1.814 s    10 runs
2021-03-23 17:45:02 -04:00
..
2021-01-30 18:22:48 -05:00
2021-03-23 17:45:02 -04:00