@gopivalleru I'll put it this way: I want it to be safe to use all of the time, but it's a bit of an open question.

Class reification is pretty aggressive about generating JVM classes for all normal Object descendants (not for singleton classes or descendants of other core Ruby types). These classes are generated into their own classloaders, so that if the Ruby class goes away, the JVM class goes away... but that sometimes takes a few GC cycles to flush out.

I do not know of a reason why it could not work fine in production but as it has not typically been run that way, I don't have a lot of hard data. The most likely concerns for you would be:

• Old JRuby version: There's been several fixes to class reification since 9.2.8.0. I would be fairly comfortable recommending you try enabling reification in production on JRuby 10 or 9.4, but earlier versions will carry more risk.
• Your own coding patterns: Since reification will try to generate a new JVM class for every nominal (not anonymous) Object descendant, libraries that continually generate new classes will see perf impact (at best) and potentially memory leaks or GC pressure (at worst).
• Increased memory use: Regardless of what version of JRuby you use, there will be an associated increase in memory use, especially involving "off heap" JVM memory used to manager things like class and method data. It may be a small increase (just one JVM class per Ruby class, not increased memory for the objects themselves) but it's something to keep in mind.

I suspect you are interested in this to diagnose some other problem... am I right? There's little value in enabling reification globally for most apps unless you need to use JVM tooling to inspect the heap and want to see real JVM classes rather than lots of RubyObject* instances.

So here's what I would suggest to you:

• Add information about your JRuby usage to https://github.com/jruby/jruby/blob/master/USERS.md. We're trying to get a better picture of how people use JRuby, both for future development and for new users coming to the project for the first time.
• Consider upgrading. JRuby 9.2.8.0 is quite old at this point, and along with many bug fixes there's sure to also be missing security patches. We've also steadily improved memory use and performance since then.
• If you need a JRuby expert on your team, consider getting in touch with me through Headius Enterprises, the company I started to help fund JRuby development and support JRuby users. We can provide an expert "virtual team member" to help you with problem diagnosis and JRuby upgrades. You can also contact me directly via my GitHub profile.

I am happy to answer additional questions here, but I strongly suggest you consider upgrading your app and getting expert help to diagnose any issues you're having. I guarantee you'll be a happier JRuby user as a result.