Linked by Thom Holwerda on Sat 19th Sep 2015 14:29 UTC, submitted by Pete

Interestingly, the entirety of Google's codebase - from search and maps to YouTube and Google Docs - resides in a monolithic source code repository available to and used by 95% of Google engineers, or about 25,000 users to be exact.

"Without being able to prove it," a Google engineering manager said, "I'd guess that this is probably the largest single repository in use anywhere in the world."

All told, Google's services comprise 2 billion lines of code which, taken together, weigh in at 86 terabytes.


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There is more detail
by sukru on Mon 21st Sep 2015 05:33 UTC
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There are more details in this presentation:

Google really uses a monolithic code base for most of the stuff. Externally shared ones like Chromium, and Android are separate, but the main code is in one place.

We see a "cloud" based view of the latest version of the repository. While it is possible to have branches, that is rare, any real code change will be to the "head". The presentation goes into more details, but basically we have a system called TAP that makes sure you do not break anybody else's code.

It is really nice, and works well, let me give a concrete example.

Recently I was working on a tool, that uses a library to connect to a service. I would benefit from recent changes to the service, and instead of waiting the library owner, or the service owner to adapt them, I put together a patch, got it reviewed, checked in and got my use case done.

However it inadvertently broke somebody else's code, and we missed that during regular tests. While I was getting together what was wrong, a (fifth?) party came in, and sent the fix.

Everything was better. The new service features were adopted, bugs were fixed (even some older things got optimized), tests were updated, and we went on our ways.

Edited 2015-09-21 05:34 UTC

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