Re: vc-dir operation is very slow on large git repositories in Emacs 26.1

[Alex Harsanyi <alexharsanyi@gmail.com>]

On Wed, Jun 20, 2018 at 11:51 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>> From: Alex Harsanyi <alexharsanyi@gmail.com>
>> Date: Wed, 20 Jun 2018 18:50:12 +0800
>>
>> I have a somewhat large git repository at work (51556 files) and
>> Emacs 26.1 is very slow when updating the *vc-dir* buffer: I
>> start emacs with the "-Q -no-site-file" and it takes
>> approximately 2 minutes to update the vc-dir buffer. Emacs 25.2,
>> on the same machine and repository, will complete this operation
>> in a few seconds.  This is on a Windows machine and I use the
>> prebuilt binaries downloaded from the gnu.org website for both
>> versions.
>>
>> The operation that takes a long time is the ls-files
>> operation, "git --no-pager ls-files -z -c -s --", but running
>> that command in a terminal completes in less than a second.
>
> So you are saying that in Emacs 25.2 this slow Git command was not
> invoked in your scenario?
>

I do not say that.  Emacs 25.2 completes too fast to be able to
figure what is going on.  I suspect 25.2 uses the same git
command though, as the command itself completes quickly.

>> I cloned the Emacs git repository (which has 3683 files) and a
>> vc-dir operation in Emacs 26.1 takes 7 seconds on my machine,
>> compared to less than 1 second in Emacs 25.2.  I noticed this
>> speed difference on my home computer as well.
>
> FWIW, I get about 2 sec for this in the Emacs repository, and I see no
> perceptible difference between Emacs 25.2 and Emacs 26.1.
>

I suspect this might be a problem with my environment, but I do
not know what.  It also happens on two machines: my work one and
my home one.  I would appreciate any hints on how to diagnose
this.

>> If not, I would appreciate some suggestions on how to further
>> diagnose the cause of this issue, as it seems it is related to my
>> computer.
>
> Where did you get the Emacs binaries for the 2 above-mentioned
> versions?

Both versions were downloaded as compiled binaries from the
gnu.org website and not modified in any way -- this happens when
I start Emacs with "-Q -no-site-file".

Alex.