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Comment by sa46 | Hacker News Reader

I don't understand how avoiding bitrot is better in a multi-repo setup. With a multi-repo, if you're changing a core-library you can make the change quickly but you can't upgrade clients until they upgrade on their own. You still have bitrot. The difference is that the bitrot isn't visible because it's compartmentalized into separate repos.

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So, to me, different things using different versions of the same library isn't inherently bitrot. For one, if you're actively maintaining your code, then everything's going to eventually end up upgraded. It's just a question of whether you want to boil the ocean all at once, in one big pot, or do it in a series of smaller batches.

There are legitimate arguments for both options. The thing I'm trying to say is, you should beware the idea that going monorepo means the ocean's going to just boil itself somehow.

The reason that a monorepo facilitates this kind of bit-rot is because of one of the advantages of the monorepo setup: that it also facilitates easily making connections between different parts of the codebase. In a multi-repo setup, you need to be intentional about when and how you pull in another repo, because the bar to doing so is so high. In a monorepo, every piece of every part of the code is available to you and no extra action is required to "pull in" that other repo, which means in practice that without tooling or discipline you end up with a codebase with lots of tight interconnections.

So the reason it happens in a monorepo more is that those connections are easier to make and therefore a lot more common, not because those connections are impossible in a multi-repo setup.

I see, the argument is that monorepo facilitates tight-coupling because it's easy to add dependencies. The multi-repo doesn't have the same problem because it's more difficult to have cross module dependencies.

There's a number of solutions to prevent tight-coupling.

1. Language-level visibility modifiers. 2. Build system visibility. Bazel offers fine-grained visibility. I'm not sure about others. 3. Using RPCs as the primary interconnect between services.

My view is that disadvantages of tight-coupling in a mono-repo is a much better problem to have than the disadvantages of having logic spread across different repos.

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