bug#64735: 29.0.92; find invocations are ~15x slower because of ignores

[Ihor Radchenko]

Eli Zaretskii <eliz@gnu.org> writes:

>> > (length (directory-files-recursively "~/Git" ""))
>> > ;; => 113628
>> > (benchmark-run-compiled 1 (directory-files-recursively "~/Git" ""))
>> > ;; => (1.597328425 1 0.47237324699997885)
>> > (benchmark-run-compiled 1 (let (file-name-handler-alist) 
>> > (directory-files-recursively "~/Git" "")))
>> > ;; => (1.0012111910000001 1 0.4860752540000135)
> ...
> The figures provided in this thread indicate speedups that are modest
> at best, so I'm not sure they justify measures which could cause
> problems (if that indeed could happen).

Not that modest. Basically, it all depends on how frequently Emacs file API is
being used. If we take `find-lisp-find-files', which triggers more file
handler lookup, the difference becomes more significant:

(benchmark-run-compiled 1 (find-lisp-find-files "/home/yantar92/.data" ""))
;; (3.853305824 4 0.9142656910000007)
(let (file-name-handler-alist) (benchmark-run-compiled 1 (find-lisp-find-files 
"/home/yantar92/.data" "")))
;; (1.545292093 4 0.9098995830000014)

In particular, `expand-file-name' is commonly used in the wild to ensure
that a given path is full. For a single file, it may not add much
overheads, but it is so common that I believe that it would be worth it
to make even relatively small improvements in performance.

I am pretty sure that file name handlers are checked behind the scenes
by many other common operations.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
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