Merge pull request DataDog#2887 from DataDog/rgs/metrics-report-logging

debug logging for metrics system

Author: richardstartin

dd-trace-core/src/main/java/datadog/trace/common/metrics/Aggregator.java

@@ -83,15 +83,20 @@ public void run() {
         }
       } catch (InterruptedException e) {
         currentThread.interrupt();
+      } catch (Throwable error) {
+        log.debug("error aggregating metrics", error);
       }
     }
+    log.debug("metrics aggregator exited");
   }
 
   private void report(long when) {
+    boolean skipped = true;
     if (dirty) {
       try {
         expungeStaleAggregates();
         if (!aggregates.isEmpty()) {
+          skipped = false;
           writer.startBucket(aggregates.size(), when, reportingIntervalNanos);
           for (Map.Entry<MetricKey, AggregateMetric> aggregate : aggregates.entrySet()) {
             writer.add(aggregate.getKey(), aggregate.getValue());
@@ -106,6 +111,9 @@ private void report(long when) {
       }
       dirty = false;
     }
+    if (skipped) {
+      log.debug("skipped metrics reporting because no points have changed");
+    }
   }
 
   private void expungeStaleAggregates() {

dd-trace-core/src/main/java/datadog/trace/common/metrics/ConflatingMetricsAggregator.java

@@ -130,8 +130,10 @@ public void start() {
               reportingInterval,
               reportingInterval,
               reportingIntervalTimeUnit);
+      log.debug("started metrics aggregator");
     } else {
       enabled = false;
+      log.debug("metrics aggregator not started because sink could not be validated");
     }
   }
 
@@ -143,6 +145,9 @@ public boolean report() {
       published = inbox.offer(REPORT);
       ++attempts;
     } while (!published && attempts < 10);
+    if (!published) {
+      log.debug("Skipped metrics reporting because the queue is full");
+    }
     return published;
   }
 

dd-trace-core/src/main/java/datadog/trace/common/metrics/MetricsAggregatorFactory.java

@@ -1,12 +1,18 @@
 package datadog.trace.common.metrics;
 
 import datadog.trace.api.Config;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 public class MetricsAggregatorFactory {
+  private static final Logger log = LoggerFactory.getLogger(MetricsAggregatorFactory.class);
+
   public static MetricsAggregator createMetricsAggregator(Config config) {
     if (config.isTracerMetricsEnabled()) {
+      log.debug("tracer metrics enabled");
       return new ConflatingMetricsAggregator(config);
     }
+    log.debug("tracer metrics disabled");
     return NoOpMetricsAggregator.INSTANCE;
   }
 }

dd-trace-core/src/main/java/datadog/trace/common/writer/ddagent/DDAgentFeaturesDiscovery.java

@@ -95,6 +95,13 @@ public void discover() {
         }
       }
     }
+    if (log.isDebugEnabled()) {
+      log.debug(
+          "discovered traceEndpoint={}, metricsEndpoint={}, supportsDropping={}",
+          traceEndpoint,
+          metricsEndpoint,
+          supportsDropping);
+    }
   }
 
   private String probeTracesEndpoint() {