[llvm-dev] GitHub Hooks

Mehdi Amini via llvm-dev llvm-dev at lists.llvm.org
Tue Jul 19 15:16:38 PDT 2016

> On Jul 19, 2016, at 2:59 PM, Renato Golin <renato.golin at linaro.org> wrote:
> On 19 July 2016 at 22:35, Mehdi Amini <mehdi.amini at apple.com> wrote:
>> Claiming that it "will be *a lot* less” burden that now is easy, but I don’t see any obvious fact to back this up.
>> What is the current maintenance requirement of SVN/Git? Can someone who knows provides some fact?
> I'll let Anton tell his side, and Tanya talk about the real costs, but
> here are some facts I know:
> Our ARM/AArch64 buildbots fail around 2~3 times a month with SVN
> errors. Sometimes it's only the fast ones, sometimes all of them
> (depends on how long it takes to fix).

That’s relevant data.

> Sometimes the fix is just
> "wait", sometimes Anton has to actively fix it. (he also has to work,
> sleep, eat, etc).
> In the past, we were hit by web spiders that ignored completely the
> robots.txt file. Anton has made that better, but it can escalate if
> the spider realise we blocked them. There are ways to work around, but
> not without accidentally blocking innocent people (mostly in China).

That’s not relevant: this is about the WWW server, it does not have to be related to the hosting the repos.

> The cost of the AWS servers is ~$5k / year. It's not *only* for SVN,
> but also for web servers and hosting packages. Recently we turned off
> the deb hosting because of budget (our server and bandwidth couldn't
> cope with it).


> So, while $5k/year might not look like much, it's enough to pay a lot
> of students to go to the LLVM events, that couldn't otherwise go.

Moving the SVN repo does not solve hosting videos, Debian packages, etc.
I suspect most of the bandwidth does not come from `svn up` or `git pull`.

> It's
> also nowhere near what we would like if we were to host a robust
> repository with the features that GitHub can provide.

Like… proper hooks?

> Mainly
> bandwidth, storage, stability and support.
> Given the AWS costs that I've seen at Linaro, we'd have to *at least*
> double that money to host a dedicated machine with enough bandwidth to
> have repositories, binaries, videos etc. not counting paying someone
> to actively maintain it, if we want to compare one to one with what
> GitHub provides for free.

You’re again conflating svn/git and hosting “binaries and videos”. I don’t think we ever planned to host these on github?

> I will make no attempt at estimating Anton's time, or Tanya's or
> anyone else's, but I believe they (and their companies/universities)
> would very much rather they work on actual compiler stuff. I'm sure
> that, if we join the human cost, it'll far outweigh the infrastructure
> costs, even if we double/triple our current spending.

Possibly, I don’t know, but that’s exactly why I asked for first hand data on the subject (i.e. Anton and/or Tanya) about hosting the git/SVN repos themselves, instead of hand-wavy “I believe” discussions.

> On the other hand, as Tim has shown, a web-service with a JSON file
> will be running some web server which is light and cheaper than a
> normal web-page to deliver (less content, less bandwidth, less
> storage, less I/O), and could serve hundreds, if not thousands of
> queries per second with a small AWS image.
> The web-hooks would be setup once and hosted by GitHub, so zero
> additional work from our side, as well as all the forking, branching,
> merging, SVN interface (which we can't easily get if we move to local
> Git).
> The level of failure in the web-services will be lower (lower load,
> less probability of barfing) and even if it does, it will only affect
> the services that use it (buildbots, LNT, bisect), not any other
> developer.
> Moreover, our side of the web-service can fail catastrophically and
> need a wipe and restart, and *none* of our commit history would be
> affected. On the other hand, if the SVN fails catastrophically today,
> I don't know if we have a good backup policy that will mean commits
> could be lost. GitHub may not provide guarantees, but they do have
> proper backup policies.
> All in all, may not look much, but running a decent and stable web
> service with so much at stake is *not* a simple task, and we shouldn't
> take it for granted.

Sure, "running a decent and stable web service is not a simple task”, that’s what I’m saying.


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