[Python-Dev] How to watch buildbots?

Ivan Pozdeev vano at mail.mipt.ru
Fri Jun 1 02:13:56 EDT 2018

On 30.05.2018 16:36, Nick Coghlan wrote:
> On 30 May 2018 at 22:30, Ivan Pozdeev via Python-Dev 
> <python-dev at python.org <mailto:python-dev at python.org>> wrote:
>     What's the big idea of separate buildbots anyway? I thought the
>     purpose of CI is to test everything _before_
>     it breaks the main codebase. Then it's the job of the contributor
>     rather than maintainer to fix any breakages.
>     So, maybe making them be driven by Github checks would be a better
>     time investment.
>     Especially since we've got VSTS checks just recently, so whoever
>     was doing that still knows how to interface with this Github
>     machinery.
>     If the bots cancel a previous build if a new one for the same PR
>     arrives, this will not lead to a significant load difference 'cuz
>     the number of
>     actively developed PRs is stable and roughly equal to the number
>     of merges according to the open/closed tickets dynamics.
> There are a few key details here:
> 1. We currently need to run post-merge CI anyway, as we're not doing 
> linearised commits (where core devs just approve a change without 
> merging it, and then a gating system like Zuul ensures that the tests 
> are run against the latest combination of the target branch and the PR 
> before merging the change)

This is the only point here that looks valid (others can be refuted). 
This technique limits the achievable commit rate by 1/testing_time . Our 
average rate probably fits into this, though it still means delays.

> 2. Since the buildbots are running on donated dedicated machines 
> (rather than throwaway instances from a dynamic CI provider), we need 
> to review the code before we let it run on the contributed systems
> 3. The buildbot instances run *1* build at a time, which would lead to 
> major PR merging bottlenecks during sprints if we made them a gating 
> requirement
> 4. For the vast majority of PRs, the post-merge cross-platform testing 
> is a formality, since the code being modified is using lower level 
> cross-platform APIs elsewhere in the standard library, so if it works 
> on Windows, Linux, and Mac OS X, it will work everywhere Python runs
> 5. We generally don't *want* to burden new contributors with the task 
> of dealing with the less common (or harder to target) platforms 
> outside the big 3 - when they do break, it often takes a non-trivial 
> amount of platform knowledge to understand what's different about the 
> platform in question
> Cheers,
> Nick.
> P.S. That said, if VSTS or Travis were to offer FreeBSD as an option 
> for pre-merge CI, I'd suggest we enable it, at least in an advisory 
> capacity - it's a better check against Linux-specific assumptions 
> creeping into the code base than Mac OS X, since the latter is 
> regularly different enough from other *nix systems that we need to 
> give it dedicated code paths.
> -- 
> Nick Coghlan   | ncoghlan at gmail.com <mailto:ncoghlan at gmail.com> |   
> Brisbane, Australia


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