A developer came to me the other day asking for help in diagnosing some issues with their application and the interaction with Oracle's Coherence product. I wanted to write some testing harness to quickly test some Coherence configuration and gave some thought about how I would go and try to replicate the issues that the application had. I wanted a REPL environment so that I can interactive manipulate the Coherence API and dump outputs on demand. I decided to use Clojure to experiment with Coherence, although I could have used JRuby, Jython, Groovy or Scala. From purely a familiarity perspective, I would rank my usage of these listed languages in the order of Ruby first, Python second, Groovy third, Clojure fourth and Scala last. But for some unknown, deep-seated and probably emotional reasons, I like Clojure more and relish the opportunity to use it. One of the first thing I tried with Clojure and Coherence is to perform a timing test on adding data to a 2 node distributed cache in serial vs concurrent mode. Here's the example Clojure script:
(import '(org.apache.commons.lang3 RandomStringUtils) '(java.math BigInteger) '(java.util Random Date HashMap) '(com.tangosol.net NamedCache CacheFactory CacheService Cluster)) (CacheFactory/ensureCluster) (def cache (CacheFactory/getCache "sandbox")) (defn random-text  (RandomStringUtils/randomAlphanumeric 1048576)) (defn random-key  (RandomStringUtils/randomAlphanumeric 12)) ; Testing serial puts (new Date) (dotimes [_ 200] (.put cache (random-key) (random-text))) (new Date) ; Testing concurrent puts (def buffer (new HashMap)) (new Date) (dotimes [_ 200] (.put buffer (random-key) (random-text))) (.putAll cache buffer) (new Date)
Running this code showed a 2x gain in speed of data load. On one of the Coherence nodes, I had JVisualVM connected to it and watched the realtime GC behaviors with VisualGC. It has been fascinating to watch the behaviorial differences between serial vs parallel data load and the memory activities of the Coherence node when my Clojure script was idle. I hope to conduct more tests in the future looking at GC behaviors and leverage my Clojure script as load driver in my testing efforts and assist me in GC tuning of Coherence instances.