rust hg status

Augie Fackler raf at
Tue Feb 19 10:46:46 EST 2019

On Fri, Feb 15, 2019 at 02:39:44PM -0500, Valentin Gatien-Baron wrote:
> Hello,
> I wrote a fraction of hg status in rust, just the minimum needed to
> compare current revision and working copy with few of the flags and
> config settings supported. As you can imagine, the goal was better
> performance.  Before trying to upstream bits of this, I figured I'd
> check there's interest for this change in particular, or this kind
> of changes in general (I suspect rust would bring significant
> improvements to hg cat or hg files). The rest of this mail is more
> details.

This sounds _very_ promising and I'd love to see what you've got!

> While the implementation doesn't handle every uncommon situation right
> and could use some serious cleanup, it's an interesting performance
> improvement. In a repository with 100k tracked files and 500k ignored
> files, in the best case and measuring on a good machine:
> - hg-rs st takes ~50ms
> - hg-rs st -mard takes ~14ms
> - hg-rs st -u takes ~39ms
> By contrast, hg+chg+fsmonitor's best case is 110ms regardless of
> flags. Without fsmonitor, we're talking about 2.4s for hg st or hg st
> -u, and 400ms for hg st -mard. As a baseline, hg st --syntax-error
> takes 12ms.

Fascinating! Are you using re2 or Python's built-in re?

> A ratio of x2 compared with fsmonitor+chg is nice, but while neither
> best case is what you get all the time, fsmonitor degrades pretty
> badly, oftentimes in hard to understand ways, making for an
> unpredictable experience that is frequently bad.
> Say you change the hgignore, the rust version will take 300ms, the
> fsmonitor version will take 4.4s (I think 2s timeout + 2.4s regular
> status).
> Say you remove a directory at the root of the repository, 50ms rust
> vs 4.4s fsmonitor.
> Say you haven't used a particular share in some time, you may well see
> 1s rust vs 4.4s fsmonitor.
> So I think there's a lot of value in having status without fsmonitor
> going much faster:
> - increase significantly the scale at which fsmonitor is needed
> - improve the bad cases of fsmonitor (or even the fast path depending
> on how things are made to work together)
> Regards,
> Valentin Gatien-Baron

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