Every now and then you have a dying production application at hand. And you know you need to patch it as fast as possible. So have we, and thought it would be interesting to share one of the recent war stories. In this case we had a chance to patch an application with something as simple as String.intern(). But let me start from the beginning.
The application at hand was suffering from lack of memory and not even starting up after its recent changes. The symptoms included high CPU usage after JVM restart and then a few minutes later the fatal OutOfMemoryError: heap space in the logs. A quick look into heap contents gave us a suspect – the application was loading millions of objects into a certain internal data structure.
Background check with the development team revealed that the number of objects loaded was recently multiplied by a factor of two – instead of ~five million objects the application now had to deal with approximately ten million instances in memory. This can indeed use up some heap space. But knowing the possible cause was not going to help us much – no way the business owners were willing to give up on the precious data they had just acquired.
Source : http://www.javacodegeeks.com/2013/06/reducing-memory-usage-with-string-intern.html
