Re: Watchman/inotify support and other ways to speed up git status

On Wed, Oct 28, 2015 at 12:54 AM, David Turner [off-list ref] wrote:

On Thu, 2015-10-22 at 07:59 +0200, Christian Couder wrote:

quoted

Hi everyone,

I am starting to investigate ways to speed up git status and other git
commands for Booking.com (thanks to AEvar) and I'd be happy to discuss
the current status or be pointed to relevant documentation or mailing
list threads.

From the threads below ([0], [1], [2], [3], [4], [5], [6], [7], [8]) I
understand that the status is roughly the following:

- instead of working on inotify support it's better to work on using a
cross platform tool like Watchman

- instead of working on Watchman support it is better to work first on
caching information in the index

- git update-index --untracked-cache has been developed by Duy and
others and merged to master in May 2015 to cache untracked status in
the index; it is still considered experimental

- git index-helper has been worked on by Duy but its status is not
clear (at least to me)

Is that correct?
What are the possible/planned next steps in this area? improving

We're using Watchman at Twitter.  A week or two ago posted a dump of our
code to github, but I would advise waiting a day or two to use it, as
I'm about to pull a large number of bugfixes into it (I'll update this
thread and provide a link once I do so).

Great, I will have a look at it then!

It's good, but it's not great.  One major problem is a bug on OS X[1]
that causes missed updates.  Another is that wide changes end up being
quite inefficient when querying watchman.  This means that we do some
hackery to manually update the fs_cache during various large git
operations.

I agree that in general it would be better to store or all some of this
information in the index, and the untracked-cache is a good step on
that. But with it enabled and watchman disabled, there still appears to
be 1 lstat per file (plus one stat per dir).  The stats per-directory
alone are a large issue for Twitter because we have a relatively deep
and bushy directory structure (an average dir has about 3 or 4 entries
in it).  As a result, git status with watchman is almost twice as fast
as with the untracked cache (on my particular machine).

Thanks for this detailled description.

[1] https://github.com/facebook/watchman/issues/172