Build Woes

I thought I'd back up after the /posts/delegated-builds post and expand on the nature of the build engineering problem that I've been dealing with (at my day job) on a documentation related problem.

  • we do roughly continuous deployment. All active development and editing happens in topic branches, and there's no really good reason to leave typos and what not on the site any longer than we need to.
  • we publish and maintain multiple versions of the same resource in parallel, and often backport basic changes to maintenance branches. This is great for users, and great for clarity, but is awful practically, because to deploy continuously, you have to be rebuilding.
  • all build is self-contained. This isn't strictly a requirement, and we do use some internal continuous integration tools for internal development, but at the core, for a number of reasons I think it's important that all writers be able to build the project locally:
  • as an open source project, it's important that users can easily contribute at any level. We do lots of things to make it easy for people to submit patches, but if the build isn't portable (within reason,) then it's difficult for developers to work as peers.
  • if it's difficult to view rendered content while developing, it's hard to develop well or efficiently. While I think the what-you-see-is-what-you-get model (WYSIWYG) is the wrong answer, good feedback loops are important and being able to build locally, after you make changes, whenever you want, regardless of the availability of a network connection, is terribly important.
  • the tool we use, Sphinx, in combination with the size of our resource is a bottleneck. A single publication run takes anywhere from 4:30-6 depending on the hardware, and has grows on average 30 seconds every six months. I could rant about parallelism in documentation, but basically, if you want a system that handles cross referencing and internal links, and you want to generate static content, long compile times are mostly unavoidable.

Now there are a number of tricks that we've established to fight this underlying truth: Sphinx does some dependency checking to avoid "overbuilding," which helps some, and I've done a lot of mangling in the Makefiles to make the build process more efficient for most common cases, but even so, long growing build times are inevitable.

The Sphinx part of the build has two qualities that are frustrating:

  • each build is single threaded, so it has to read all the files one by one, and then write each file one by one. You can build other output formats in parallel (with a small hack from the default makefile,) but you can't get around the speed of a single build. There is a patch in consideration for the next version that would allow the write-stage of the build to run concurrently, but that's not live yet.
  • during the read stage of the build, you can't touch the source files, and extra files in the source tree can affect or break the build, which means that for the most part you can't build and work at the same time, until now.

The solutions are often not much better than the problem:

  • use a different build tool, that was built to do incremental builds. The problem is that there aren't a lot of good options in this area, and the build is really the primary objectionable feature of the build.

  • improve the build tool, or wait for it to improve. The aforementioned patch to let the write phase run concurrently will help a lot. Having said that, it's important to keep the project on a standard public release of Sphinx and it's difficult to modify core Sphinx behavior from the extension system.

    Perhaps I have Stockholm Syndrome with the build, but I tend to thing that on some level this is a pretty difficult problem, and building a safe concurrent build system is hard there aren't a lot of extant solutions. At the same time, this blog is about 2.5 times as large as the documentation project and can do a complete rebuild in 20% of the time or less as much time. While the blog is probably a little less complex, they're largely similar and it's not 5-6 times less complex.

    I think the problem is that people writing new documentation systems have to target and support new users and smaller test projects, that by the time people have serious problems with the road blocks, the faulty designs are too baked in.

  • brute force the problem by making use non-local build infrastructure that has faster less contentious processor and disk resources. This sounds good, except our test machines are pretty fast, and the gains made by better hardware don't keep up with continued growth. While we might gain some speed by moving builds off of our local machines, the experience is quite worse. Furthermore, we do build-non locally, and that's great, but it's not a replacement.

There aren't a lot of solutions and most of them seem to come down to "deal with it and build less," which is hardly a solution.

This is the foundation of the /posts/delegated-builds script that I wrote, which addresses the problem by making it less intrusive. I'm also working on a brief FAQ, which might help address some of the big questions about this project.

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