[nicktelford]

I find it a bit bizarre that this JEP doesn't enable Compact Object Headers by default. Most users will not know to specifically enable it, so if they're that confident in its stability and performance, why not enable it for everyone?

The JVM used to have a reputation for requiring byzantine flags to properly optimise its performance (mostly GC configuration). We've mostly left that behind these days, but it feels like JEP 519 takes a step backwards here.

[jeroenhd]

The JVM world is slow and extremely careful. If there's a chance something that once works breaks, it'll take many years before the change is applied by default.

Many JVM users can make huge performance gains by switching the GC to a better once and by toggling all kinds of options.

[zaphirplane]

That would be the LTS track. A change has no effect on the LTS version which is supported for a long time

[pron]

These things tend to be done gradually out of an abundance of caution. Assuming the experience remains positive, it will be made the default in some future release.