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Why Facebook does not use Git – and why most other devs do • DEVCLASS (devclass.com)

submitted 4 months ago by AnActOfCreation to c/programming

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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] 8 points 4 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 4 months ago (1 children)

Commit IDs are only local anyway.

Whay do you mean by that?

[–] [email protected] 3 points 4 months ago (1 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.

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

Got it! Are they renumbered chronologically? Like if my 11 was created before your 11, would yours be the one that's renumbered?

[–] [email protected] 2 points 4 months ago

No. They are not renumbered. Your 11 is always the same commit. It's consistent locally (which is what I mean by "local only") otherwise they'd change under your feet. You just can't share them with others and expect the same results. You have to use the hash for that.

[–] FizzyOrange 2 points 4 months ago (1 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.

[–] aport 1 points 4 months ago (1 children)

Old, unreachable commits will be garbage collected.

[–] FizzyOrange 2 points 4 months ago (1 children)

Does that not happen with Mercurial? If not that seems like a point against it.

[–] aport 1 points 4 months ago (1 children)

I'm confused, the behavior you just said was "exactly the same in git" is now a problem for Mercurial?

[–] FizzyOrange 1 points 4 months ago (1 children)

I thought it was exactly the same based on the description.

[–] [email protected] 1 points 4 months ago* (last edited 4 months ago)

No the old commit is always there, marked as obsolete with the information of what it became. No holes in history. (Assuming you use the obsolecense markers)