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SourceFS: A 2h+ Android build becomes a 15m task with a virtual filesystem

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137 points cdesai | 1 comments | 22 Oct 25 12:39 UTC | HN request time: 0s | source
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Ericson2314 ◴[22 Oct 25 15:46 UTC] No.45670912[source]▶
The headline times are a bit ridiculous. Are they trying to turn https://github.com/facebook/sapling/blob/main/eden/fs/docs/O... or some git fuse thing into a product?
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zokier ◴[22 Oct 25 15:55 UTC] No.45671060[source]▶
Well they also claim to be able to cache build steps somehow build-system independently.

> As the build runs, any step that exactly matches a prior record is skipped and the results are automatically reused

> SourceFS delivers the performance gains of modern build systems like Bazel or Buck2 – while also accelerating checkouts – all without requiring any migration.

Which sounds way too good to be true.

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vlovich123 ◴[22 Oct 25 16:57 UTC] No.45671987[source]▶
Yeah, I agree. This part is hand waved away without any technical description of how they manage to pull this off since knowing what is even a build step and what dependencies and outputs are are only possible at the process level (to disambiguate multi threaded builds). And then there’s build steps that have side effects which come up a lot with CMake+ninja.
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rcxdude ◴[22 Oct 25 18:14 UTC] No.45673038{3}[source]▶
A fuse filesystem can get information about the thread performing the file access: https://man.openbsd.org/fuse_get_context.3

So they could in principle get a full list of dependencies of each build step. Though I'm not sure how they would skip those steps without having an interposer in the build system to shortcut it.

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1. vlovich123 ◴[22 Oct 25 19:45 UTC] No.45674200{4}[source]▶
Yeah that’s what I meant. I bet you the build must be invoked through a wrapper script that interposes all executables launched within the product tree. Complicated but I think it could work. Skipping steps correctly is the hard part but maybe you do that in terms of knowing somehow the files that will be accessed ahead of time by that processes and then skipping the launch and materializing the output (they also mention they have to run it once in a sandbox to detect the dependencies). But still, side effects in build systems seem difficult to account for correctly; I bet you that’s why it’s a “contact us” kind of product - there’s work needed to make sure it actually works on your project.