git - 是否有重复的 SHA 提交？

Question

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Answer 1

Is there duplicated hashes taken every repository of the whole world?

可能是，但极不可能。让我引用 Git book关于这个，其中包含一个非常说明性的示例:

A lot of people become concerned at some point that they will, by random happenstance, have two objects in their repository that hash to the same SHA-1 value. What then?

If you do happen to commit an object that hashes to the same SHA-1 value as a previous object in your repository, Git will see the previous object already in your Git database and assume it was already written. If you try to check out that object again at some point, you’ll always get the data of the first object.

[...]

Here’s an example to give you an idea of what it would take to get a SHA-1 collision. If all 6.5 billion humans on Earth were programming, and every second, each one was producing code that was the equivalent of the entire Linux kernel history (3.6 million Git objects) and pushing it into one enormous Git repository, it would take roughly 2 years until that repository contained enough objects to have a 50% probability of a single SHA-1 object collision. A higher probability exists that every member of your programming team will be attacked and killed by wolves in unrelated incidents on the same night.

简而言之:是的，SHA1 冲突在理论上是可能的，但在天文数字上不太可能，以至于 Git 根本不考虑这种情况。