[core] Add Utils.getGCStats() to return a map of stats for each garbage

collector. This will allow greater insight into the generations.
Now the client will emmit the stats for each collector at the end of
run along with the totals.

core/src/main/java/com/yahoo/ycsb/Client.java

@@ -30,6 +30,7 @@ import java.util.Enumeration;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Map.Entry;
 import java.util.Properties;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
@@ -696,10 +697,20 @@ public class Client
       double throughput = 1000.0 * (opcount) / (runtime);
       exporter.write("OVERALL", "Throughput(ops/sec)", throughput);
       
-      exporter.write("TOTAL_GCs", "Count", Utils.getGCTotalCollectionCount());
-      final long gcTime = Utils.getGCTotalTime();
-      exporter.write("TOTAL_GC_TIME", "Time(ms)", gcTime);
-      exporter.write("TOTAL_GC_TIME_%", "Time(%)", ((double)gcTime / runtime) * (double)100);
+      final Map<String, Long[]> gcs = Utils.getGCStatst();
+      long totalGCCount = 0;
+      long totalGCTime = 0;
+      for (final Entry<String, Long[]> entry : gcs.entrySet()) {
+        exporter.write("TOTAL_GCS_" + entry.getKey(), "Count", entry.getValue()[0]);
+        exporter.write("TOTAL_GC_TIME_" + entry.getKey(), "Time(ms)", entry.getValue()[1]);
+        exporter.write("TOTAL_GC_TIME_%_" + entry.getKey(), "Time(%)",((double)entry.getValue()[1] / runtime) * (double)100);
+        totalGCCount += entry.getValue()[0];
+        totalGCTime += entry.getValue()[1];
+      }
+      exporter.write("TOTAL_GCs", "Count", totalGCCount);
+      
+      exporter.write("TOTAL_GC_TIME", "Time(ms)", totalGCTime);
+      exporter.write("TOTAL_GC_TIME_%", "Time(%)", ((double)totalGCTime / runtime) * (double)100);
       if (statusthread != null && statusthread.trackJVMStats()) {
         exporter.write("MAX_MEM_USED", "MBs", statusthread.getMaxUsedMem());
         exporter.write("MIN_MEM_USED", "MBs", statusthread.getMinUsedMem());

core/src/main/java/com/yahoo/ycsb/Utils.java

@@ -20,7 +20,9 @@ package com.yahoo.ycsb;
 import java.lang.management.GarbageCollectorMXBean;
 import java.lang.management.ManagementFactory;
 import java.lang.management.OperatingSystemMXBean;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.Random;
 
 /**
@@ -240,4 +242,32 @@ public class Utils
         }
         return time;
       }
+
+      /**
+       * Returns a map of garbage collectors and their stats.
+       * The first object in the array is the total count since JVM start and the
+       * second is the total time (ms) since JVM start. 
+       * If a garbage collectors does not support the collector MXBean, then it
+       * will not be represented in the map.
+       * @return A non-null map of garbage collectors and their metrics. The map
+       * may be empty.
+       */ 
+      public static Map<String, Long[]> getGCStatst() {
+        final List<GarbageCollectorMXBean> gcBeans = 
+            ManagementFactory.getGarbageCollectorMXBeans();
+        final Map<String, Long[]> map = new HashMap<String, Long[]>(gcBeans.size());
+        for (final GarbageCollectorMXBean bean : gcBeans) {
+          if (!bean.isValid() || bean.getCollectionCount() < 0 || 
+              bean.getCollectionTime() < 0) {
+            continue;
+          }
+          
+          final Long[] measurements = new Long[] {
+              bean.getCollectionCount(),
+              bean.getCollectionTime()
+          };
+          map.put(bean.getName().replace(" ", "_"), measurements);
+        }
+        return map;
+      }
 }

core/src/test/java/com/yahoo/ycsb/TestUtils.java

@@ -112,8 +112,10 @@ public class TestUtils {
     assertTrue(Utils.getGCTotalCollectionCount() >= 0);
     // Could be zero similar to GC total collection count
     assertTrue(Utils.getGCTotalTime() >= 0);
+    // Could be empty
+    assertTrue(Utils.getGCStatst().size() >= 0);
   }
-  
+   
   /**
    * Since this version of TestNG doesn't appear to have an assertArrayEquals,
    * this will compare the two to make sure they're the same.