bug#46859: 28.0.50; [PATCH]: Add option to truncate long lines in xref.el

[Dmitry Gutov <dgutov@yandex.ru>]

On 06.03.2021 14:54, Gregory Heytings wrote:
>> Also: grepping for that kind of regexp is noticeably slower than 
>> grepping for 'file'. Or even '.file'. Like 85ms vs 7ms slower.
>>
> 
> Well, the bug report mentioned delays of 3-4 seconds on files with very 
> long lines, so I'd guess that 85 ms is a pretty reasonable speed...

We do want fast searches to remain fast, too.

I got that 85ms timing when searching just one file. A project can often 
contain thousands of files.

In my further testing, the difference is not as stark because of other 
Elisp overhead on file listing, serialization/deserialization/process 
calls/parsing output, but even with all that in my work project the 
difference between such searches can be 0.27s vs 0.43s.

With further optimizations of project file listing logic, the difference 
can become even more pronounced (project-files in the same project takes 
0.14s).

You can benchmark it yourself with this form:

(benchmark 1 '(project-find-regexp ".\\{0,100\\}file.\\{0,100\\}"))

vs

(benchmark 1 '(project-find-regexp "file"))

(I get 9s vs 7s in the same project for this particular search).