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JRuby with Java 8 4 to 10 times slower than Java 7 #1858
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.
Any tips on hunting down the performance problem would be appreciated.