We are attempting to migrate our Rails 3.2 app to Java 8. It runs fine with JRuby 1.7.9 under Java 6 and Java 7 (Java 7 is a bit faster). However, under Java 8, my tests took 42 minutes elapsed time instead of about 7 minutes. Nobody else seems to have seen this. My colleague has the same issue, and it also happens on a Centos machine we use for testing.

I don't believe it is a problem of memory, as we are giving JAVA 500MB more memory to play with than Java 7.

When we look at execution times of request handling, ActiveRecord (using jdbc-postgres) seems fast but rendering templates takes a very long time. So I suspect String building may be the cause of it.

Versions:
JRuby 1.7.9 or 1.7.13
Java 1.8.0_11 64-Bit Server build 25.11-b03.
Ubuntu 12.04 (Don't know the version of Centos on test machine)
JAVA_OPTS="-Xms512m -Xmx2096m -Djava.net.preferIPv4Stack=true"

Any tips on hunting down the performance problem would be appreciated.