I was a witness to a decision on whether to migrate an old Java project to Go. A proof of concept (a Go rewrite of a core part of the engine) convincingly showe

I was a witness to a decision on whether to migrate an old Java project to Go. A proof of concept (a Go rewrite of a core part of the engine) convincingly showed that the Go version would be somewhat more performant, would have vastly better startup time, and would have a smaller and simpler codebase, since the Java version's caches and latency-hiding complexity would not be needed. The decision made was to stick with Java. Why? Because rewriting the long feature tail of the Java version in Go and ensuring bug-for-bug compatibility with the Java version would have taken multiple engineer-years. During the rewrite, from the perspective of the project's users, development would have stalled. It made more business sense to instead use those engineer-years to implement some new features that users were demanding. And after all, while the Java version's performance wasn't amazing, it was acceptable.