Fixed OOM for json metrics output (#92)

* Fixed OOM for json metrics output

* Reworked code a bit to match current code style

pom.xml

@@ -4,7 +4,7 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>com.yugabyte</groupId>
   <artifactId>yb-sample-apps</artifactId>
-  <version>1.3.10-SNAPSHOT</version>
+  <version>1.3.11-SNAPSHOT</version>
   <name>YB Sample Apps</name>
   <description>
     Sample applications for benchmarking YugaByte DB functionality on various workload types.

src/main/java/com/yugabyte/sample/common/metrics/Metric.java

@@ -16,17 +16,21 @@
 import com.google.gson.JsonObject;
 
 public class Metric {
-  private ReadableStatsMetric readableStatsMetric;
-  private JsonStatsMetric jsonStatsMetric;
+  private final boolean outputJsonMetrics;
+
+  private final ReadableStatsMetric readableStatsMetric;
+  private final JsonStatsMetric jsonStatsMetric;
+
+  public Metric(String name, boolean outputJsonMetrics) {
+    this.outputJsonMetrics = outputJsonMetrics;
 
-  public Metric(String name) {
     readableStatsMetric = new ReadableStatsMetric(name);
     jsonStatsMetric = new JsonStatsMetric(name);
   }
 
   public synchronized void observe(Observation o) {
     readableStatsMetric.accumulate(o.getCount(), o.getLatencyNanos());
-    jsonStatsMetric.observe(o);
+    if (outputJsonMetrics) jsonStatsMetric.observe(o);
   }
 
   public String getReadableMetricsAndReset() {

src/main/java/com/yugabyte/sample/common/metrics/MetricsTracker.java

@@ -52,7 +52,7 @@ public void registerStatusMessageAppender(StatusMessageAppender appender) {
 
   public synchronized void createMetric(MetricName metricName) {
     if (!metrics.containsKey(metricName)) {
-      metrics.put(metricName, new Metric(metricName.name()));
+      metrics.put(metricName, new Metric(metricName.name(), outputJsonMetrics));
     }
   }