For those short on time: "It doesn't go as planned" is explained in the middle of the article:
> When everything compiled, I shipped it. And to everyone's surprise, apart from a few bugs I had created while rewriting thousands of lines of code... it worked. It just did. No explosions, no obscure bugs, no memory leak, no performance degradation. That was rather unexpected.
...followed by
> Then we saw the JVM CPU usage rise to alarming heights, with unusual patterns. And no obvious culprit in the thread dumps...
> When everything compiled, I shipped it. And to everyone's surprise, apart from a few bugs I had created while rewriting thousands of lines of code... it worked. It just did. No explosions, no obscure bugs, no memory leak, no performance degradation. That was rather unexpected.
...followed by
> Then we saw the JVM CPU usage rise to alarming heights, with unusual patterns. And no obvious culprit in the thread dumps...
> it was just the JVM that needed some tuning.
Details: https://lichess.org/@/thibault/blog/lichess-on-scala3-help-n...