Subject: bug#66117: 30.0.50; `find-buffer-visiting' is slow when opening large number of buffers

From: Dmitry Gutov <[email-masked]>
Date: Wed, 4 Oct 2023 14:46:23 +0300

On 04/10/2023 13:58, Ihor Radchenko wrote:
> Dmitry Gutov<[email-masked]>  writes:
> 
>>> Would it be possible to implement some kind of caching mechanism to be
>>> used by `find-buffer-visiting'?
>> I'm guessing you Cc'd me because of an existing comment inside xref.el?
>> As you can see I decided not to use this function there, but even
>> get-file-buffer wasn't as fast as I would've wanted, so there's a
>> quick-and-dirty caching solution for sequential lookups (which assumes
>> that the same file would be looked up multiple times in a row).
> It looks like my example is quite different from yours.
> Do you have a reproducer demonstrating `get-file-buffer' being slow?

I retested, and it seems most people here won't be impressed by my 
example. Anyway:

1. Call (benchmark-run 1 (project-find-regexp "emacs") in an Emacs repo 
checkout.
2. Change xref--collect-matches to call get-file-buffer instead of 
xref--find-file-buffer (which does some caching). 'M-x 
byte-compile-file', (load "xref.elc"), and run the benchmark again.

What I get here, is 3.60s vs 5.03.

It's a 1.40s difference over ~95000 calls, though (this is how many 
matches are produced). Which is meaningful for my case, but probably not 
for yours.