Here at Google we have both kinds of scalability problems - loading classes from a classpath with 10,000 jars, and loading a single class file packed with the maximal number of methods. This message is about the latter.
If you have a class with ~64k methods with a superclass that also has ~64k methods, class loading that single class will cost you ~30sec and calling Class.getMethods another ~10sec. Both are unacceptably slow. I think both are due to O(N^2) algorithms, the first in hotspot, and the second in Class.java. I have the start of a fix for Class.java, but it makes the common case slower. A really good fix is harder to find. In general, I think Class.java could benefit from some performance-oriented rework. Is anyone else working on class loading performance, especially in hotspot? Here's the benchmark (that could perhaps be integrated into openjdk even without a fix) http://cr.openjdk.java.net/~martin/webrevs/openjdk9/Class.getMethods-benchmark/test/java/lang/Class/getMethods/ManyMethodsBenchmark.java.html Base class load time: 186.44 ms getDeclaredMethods: Methods: 65521, Total time: 43.27 ms, Time per method: 0.0007 ms getMethods : Methods: 65530, Total time: 60.82 ms, Time per method: 0.0009 ms Derived class load time: 33440.13 ms getDeclaredMethods: Methods: 65521, Total time: 39.71 ms, Time per method: 0.0006 ms getMethods : Methods: 65530, Total time: 11582.54 ms, Time per method: 0.1768 ms
