this post was submitted on 18 Jul 2024
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  • Facebook does not use Git due to scale issues with their large monorepo, instead opting for Mercurial.
  • Mercurial may be a better option for large monorepos, but Git has made improvements to support them better.
  • Despite some drawbacks, Git usage remains dominant with 93.87% share, due to familiarity, additional tools, and industry trends.
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[–] [email protected] 91 points 3 months ago* (last edited 3 months ago) (4 children)

Facebook uses Mercurial, but when people praise their developer tooling it's not just that. They're using their CLI which is built on top of Mercurial but cleans up its errors and commands further, it's all running on their own virtual filesystem (EdenFS), their dev testing in a customized version of chromium, and they sync code using their own in-house equivalent of GitHub, and all of it connects super nicely into their own customized version of VS Codium.

[–] [email protected] 26 points 3 months ago (3 children)
[–] [email protected] 48 points 3 months ago

The source control was so smooth and pleasant that it convinced me that git isn't the be all end all, and the general developer focus was super nice, but some of that tooling was pretty janky, poorly documented, and you had no stack overflow to fall back on. And some of it (like EdenFS), really felt like it was the duct tape holding that overloaded monorepo together (complete with all the jankiness of a duct tape solution).

[–] [email protected] 42 points 3 months ago (1 children)

What you can do with 84000 employees

[–] [email protected] 19 points 3 months ago

And some good management. Probably not a common opinion around here, but my company is not a tenth of that size, with a hundredth the number of devs, yet different teams still end up copy pasting libraries. Because it's faster than convincing management DevOps is important.

[–] [email protected] 14 points 3 months ago (1 children)

And kinda horrifying. If something goes wrong, no Google, it's straight to IT

[–] [email protected] 3 points 3 months ago (1 children)

There's probably specific ticket queues and wiki/doc spaces for each support team.

Problem with an app? Send it to the internal dev/support team. Then if needed it gets routed.

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[–] [email protected] 23 points 3 months ago (4 children)

The inhouse tooling from the massive tech companies is very cool but I always wonder how that impacts transferrable skills. I work in a much smaller shop but intentionally make tech decisions that will give our engineers a highly transferrable skill set. If someone wants to leave it should be easy to bring their knowledge to bear elsewhere.

[–] [email protected] 12 points 3 months ago (1 children)

Speaking from my own experience and a few other seniors I work with, you try to recreate solutions you like at those smaller shops. It may not be identical, but you know what's possible.

I came into a company that didn't have a system to manage errors. At my old job, errors would get grouped automatically and work can be prioritized through the groupings. The new company only handled errors when they saw it, by word of mouth.

Immediately went to work setting up a similar system.

[–] [email protected] 8 points 3 months ago

There’s also a whole industry of ex-Googlers reimplementing Google tooling as SaaS services to sell to other ex-Googlers at other companies.

There’s even a lookup table: https://github.com/jhuangtw/xg2xg

(some of those are open source projects, some are SaaS services)

[–] UFODivebomb 6 points 3 months ago

Absolutely does. Source: worked for Amazon.

[–] [email protected] 3 points 3 months ago (4 children)

The inhouse tooling from the massive tech companies is very cool

I agree. I personally know nothing about tooling like this but I went through the tooling used at rockstar for example GTA V and it was very cool to how much they have automated and made tools easier to use.

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[–] sukhmel 2 points 3 months ago

Oh, it impacts indeed. And I would expect that to be partially to keep the devs from hopping away, as they will have a hard time transferring

On the other hand, onboarding is longer and wastes more time and money of the company ¯\_(ツ)_/¯

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[–] MajorHavoc 37 points 3 months ago

I'm pleased to report that git has made significant strides, and git submodule can now be easily used to achieve a mono-repo-like level of painful jankiness.

[–] [email protected] 14 points 3 months ago (2 children)

And they're delivering a terrible product.

[–] 0x0 25 points 3 months ago

That's hardly the VCS's fault.

[–] [email protected] 19 points 3 months ago

That depends on who you believe their customer to be.

[–] Mikina 13 points 3 months ago (1 children)

My best VCS experience so far was when working with Plastic SCM. I like how it can track merges, the code review workflow is also nice, and in general it was pretty nice to work with.

Fuck Unity, who paywalled it into unusability, though. Another amazing project that was bought and killed by absurd monetization by Unity, same as Parsec.

[–] [email protected] 3 points 3 months ago (1 children)

How was Parsec before the acquisition?

I only really have experience after, and it's the only Unity product I've actually found that I like. My only major complaint is that it's not compatible with the base configuration of Palo Alto, but that's really more of a Palo Alto problem than a Parsec problem.

[–] Mikina 9 points 3 months ago* (last edited 3 months ago) (1 children)

I still use Parsec for remote, and I don't have any issue with it, it works great and I like it. However, they also did offer a free SDK (Unity plugin) to integrate remote play into your game natively (just like you can have "Invite to Steam Remote Play" button from Steam SDK), which was exactly what we needed - and Steam Remote was never working without issues for us, in comparison to Parsec which worked amazingly well every time we tried it.

I found numerous mentions of Parsec SDK and how easy it is to integrate, but after Unity bought it, I couldn't find it anywhere. Only mention was that if you need it, you should contact them.

So I did that, mentioning that we are a small team of students working on a offline co-op only 2 player game in our free time, and that since Steam Remote wasn't working for us and I have great experience with Parsec, I asked what we have to do to get access to the SDK/Unity plugin.

Unity's answer? Sure, no problem, they will be happy to give us access, with first step being that we pay them 1 000 000$ for it.

Like, wtf? Did they even read the email? How out of touch you have to be, to casually ask a small student team to pay 1 000 000$?

[–] [email protected] 3 points 3 months ago

Okay that's fair. Their pricing is awful in general, and that's especially egregious for something that used to be free

[–] [email protected] 12 points 3 months ago (1 children)

I use git daily and still wonder why I had fewer merge issues on a larger team in the 1990s with command line rcs on Solaris. Maybe we were just more disciplined then. I know we were less likely to work on the same file concurrently. I feel like I spend more time fighting the tools than I ever used to. Some of that is because of the dumb decisions that were made on our project a decade or more ago.

[–] [email protected] 10 points 3 months ago (1 children)

I know we were less likely to work on the same file concurrently.

I mean, isn't that when merge conflicts happen? Isn't that your answer?

[–] [email protected] 3 points 3 months ago (1 children)

I was trying to say that tools were better about letting us know that another developer was modifying the same file as us, so we would collaborate in advance of creating the conflict.

[–] [email protected] 3 points 3 months ago

I gotcha, I misunderstood

[–] [email protected] 11 points 3 months ago (1 children)

Mercurial does have a few things going for it, though for most use-cases it's behind Git in almost all metrics.

I really do like the fact that it keeps a commit number counter, it's a lot easier to know if "commit 405572" is newer than "commit 405488" after all, instead of Git's "commit ea43f56" vs "commit ab446f1". (Though Git does have the describe format, which helps somewhat in this regard. E.g. "0.95b-4204-g1e97859fb" being the 4204th commit after tag 0.95b)

[–] [email protected] 15 points 3 months ago (1 children)

I suspect rebasing makes sequential commit IDs not really work in practice.

[–] [email protected] 8 points 3 months ago (2 children)

Rebasing updates the commit ids. It's fine. Commit IDs are only local anyway.

One thing that makes mercurial better for rebase based flows is obsolescence markers. The old version of the commits still exist after a rebases and are marked as being made obsolete by the new commits. This means somebody you've shared those old commits with isn't left in hyperspace when they fetch your new commits. There's history about what happened being shared.

[–] AnActOfCreation 4 points 3 months ago (1 children)

Commit IDs are only local anyway.

Whay do you mean by that?

[–] [email protected] 3 points 3 months ago (2 children)

You and I both clone a repo with ten changes in it. We each make a new commit. Both systems will call it commit 11. If I pull your change into my repo your 11 becomes my 12.

The sequential change IDs are only consistent locally.

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[–] FizzyOrange 2 points 3 months ago (5 children)

That's exactly the same in git. The old commits are still there, they just don't show up in git log because nothing points to them.

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[–] [email protected] 10 points 3 months ago* (last edited 3 months ago)

As far as performance goes, Microsoft did manage to make git work for them later on (...with many contributions upstreamed and homegrown solutions developed—but then, Facebook is the same, isn't it?).

[–] [email protected] 6 points 3 months ago (1 children)

jujutsu is a fresh take on git-- you describe the work you're about to do with jj new -m 'message'. Do the work. Anything not previously ignored in .gitignore is ready to commit with jj ci. You don't have to git add anything. No futzing with stashes to switch or refocus work. Need that file back? jj restore FILENAME.

[–] AnActOfCreation 9 points 3 months ago (1 children)

It's very optimistic to think people will be able to describe what they're going to do before they do it. I find things rarely go exactly as planned and my commit messages usually include some nuance about my changes that I didn't anticipate.

[–] [email protected] 2 points 3 months ago

This is true. But at jj ci you're plonked into an editor and can change the description.

[–] [email protected] 4 points 3 months ago (1 children)
[–] FizzyOrange 13 points 3 months ago (1 children)

That brings more problems. Despite the scaling challenges monorepos are clearly the way to go for company code in most cases.

Unfortunately my company heavily uses submodules and it is a complete mess. People duplicating work all over the place, updates in submodules breaking their super-modules because testing becomes intractable. Tons of duplicate submodules because of transitive dependencies. Making cross-repo changes becomes extremely difficult.

[–] [email protected] 3 points 3 months ago (1 children)

But if not for using submodules, how can one share code between (mono-)repos, which rely on the same common "module" / library / etc.? Is it a matter of "not letting submodules usage get out of hand", sticking to an "upper limit of submodules", or are submodules to be avoided entirely for monorepos of a certain scale and there's a better option?

[–] nous 4 points 3 months ago (1 children)

You don't share code between monorepos, the whole point of a monorepo is you only have one repo where all code goes. Want to share a library, just start using it as it is just in a different directory.

Submodules are a poor way to share code between lots of small separate repos. IMO they should never be used as I have never seen them work well.

If you don't want a mono repo then have your repos publish code to artifact stores/registries that can be reused by other projects. But IMO that just adds more complexities and problems then having everything in a single repo does.

[–] [email protected] 2 points 3 months ago (1 children)

So AFAIU, if a company had:

  • frontend
  • backend
  • desktop apps
  • mobile apps

... and all those apps would share some smaller, self developed libraries / components with the frontend and/or backend, then the "no submodules, but one big monorepo" approach would be to just put all those apps into that monorepo as well and simply reference whatever shared code there might be via relative paths, effectively tracking "latest", or maybe some distinct "stable version folders" (not sure if that's a thing).

Anyway, certainly never thought to go that far, because having an app that's "mostly independant" from a codebase perspective be in it's own repo seemed beneficial. But yeah, it seems to me this is a matter of scale and at some point the cost of not having everything in a monorepo would become too great.

Thanks!

[–] FizzyOrange 2 points 3 months ago (1 children)

Yeah exactly that. Conceptually it's far superior to manyrepos. But it does have downsides:

  • git will be slower, and it doesn't really have great support for this way of working. I mean it provides raw commands for partial checkouts... but you're kind of on your own.
  • You can't realistically view a git log --graph any more since there will be just way too many commits. Though tbf you can get to that state without a monorepo if you have a big project and work with numskulls who make 50 commits for a small MR and don't squash.

Also it's not really a downside since you should be doing this anyway, but you need to use a build tool that sandboxes dependencies so it can guarantee there are no missing edges in your dependency graph (Bazel, Buck, Pants, Please, Landlock Make, etc.). Otherwise you will be constantly breaking master when things aren't checked in CI that should be.

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[–] [email protected] 3 points 3 months ago

And google uses Piper to do the same thing

https://dl.acm.org/doi/10.1145/2854146

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