hgwatchman: inotify that works

Martin Geisler martin at geisler.net
Tue Sep 3 01:57:43 CDT 2013

Siddharth Agarwal <sid0 at fb.com> writes:

> On 09/02/2013 01:09 PM, Martin Geisler wrote:
>> Siddharth Agarwal <sid0 at fb.com> writes:
>> Hey!
>> That's really cool! Thanks for the hard work you guys are putting into
>> Mercurial.
>> I tried it (after fixing some small 32-bit build errors in watchman)
> If you have time, patches for them would be appreciated. We don't have
> CI set up for 32-bit builds on any OS, so they invariably break.

My patches have already been sent and applied!

>> with the OpenOffice repo where there are 69k files in the working
>> copy. The repo is on a SSD and the time went from 0.5 sec to 0.17
>> sec.
> That sounds about right. I'd suspect the benefits of such an extension
> show up only once you hit 100-150k files or so.

Even with a "smal" repo like that, it's good to see the overhead of
querying the daemon is smaller than the speedup given.

>> For fun, I tried with the statdaemon extension I wrote a long time
>> ago. There I didn't see any performance improvement when I turned it
>> on.
>> I haven't looked at watchman in detail, but do they do something like
>> I had to do here to make sure I get a consistent view of the
>> filesystem:
>>    https://bitbucket.org/aragost/statdaemon/src/tip/shared.py#cl-60
>> That is, touch a well-known file and wait until the event thus
>> generated is seen. Assuming that FS events are delivered in FIFO
>> order, the daemon knows that it has seen all events up to the time it
>> was called when it sees the touched file.
> Yes, that's basically what we do, though we use temporary files
> instead. See
> https://github.com/facebook/watchman/blob/master/docs/cookies.markdown.

Cool, that's basically the same idea, but without having a timestamp
file lying around. Do you know if this was discussed elsewhere than on
our mailinglist:


Have you looked into porting watchman to the Windows FS monitoring API?

Martin Geisler

More information about the Mercurial-devel mailing list