Zero out the builders as soon as they are used to avoid keeping both alive when building a large array.

4 files changed, 32 insertions, 27 deletions

diff --git a/metrics-proxy/src/main/java/ai/vespa/metricsproxy/core/MetricsManager.java b/metrics-proxy/src/main/java/ai/vespa/metricsproxy/core/MetricsManager.java
index 3de4de08424..de8d2c62880 100644
--- a/metrics-proxy/src/main/java/ai/vespa/metricsproxy/core/MetricsManager.java
+++ b/metrics-proxy/src/main/java/ai/vespa/metricsproxy/core/MetricsManager.java
@@ -13,6 +13,7 @@ import com.yahoo.component.Vtag;
 
 import java.time.Duration;
 import java.time.Instant;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.LinkedHashMap;
@@ -22,6 +23,7 @@ import java.util.logging.Logger;
 import java.util.stream.Collectors;
 
 import static ai.vespa.metricsproxy.metric.ExternalMetrics.extractConfigserverDimensions;
+import static ai.vespa.metricsproxy.metric.model.processing.MetricsProcessor.applyProcessors;
 import static java.util.logging.Level.FINE;
 import static java.util.stream.Collectors.toList;
 
@@ -79,9 +81,18 @@ public class MetricsManager {
      * @return metrics for all matching services
      */
     public List<MetricsPacket> getMetrics(List<VespaService> services, Instant startTime) {
-        return getMetricsAsBuilders(services, startTime).stream()
-                .map(MetricsPacket.Builder::build)
-                .collect(Collectors.toList());
+        MetricsPacket.Builder [] builderArray = getMetricsBuildersAsArray(services, startTime);
+        List<MetricsPacket> metricsPackets = new ArrayList<>(builderArray.length);
+        for (int i = 0; i < builderArray.length; i++) {
+            metricsPackets.add(builderArray[i].build());
+            builderArray[i] = null; // Set null to be able to GC the builder when packet has been created
+        }
+        return metricsPackets;
+    }
+
+    public MetricsPacket.Builder [] getMetricsBuildersAsArray(List<VespaService> services, Instant startTime) {
+        List<MetricsPacket.Builder> builders = getMetricsAsBuilders(services, startTime);
+        return builders.toArray(new MetricsPacket.Builder[builders.size()]);
     }
 
     /**
diff --git a/metrics-proxy/src/main/java/ai/vespa/metricsproxy/http/ValuesFetcher.java b/metrics-proxy/src/main/java/ai/vespa/metricsproxy/http/ValuesFetcher.java
index 8d5c1655df0..8f7f1c8a779 100644
--- a/metrics-proxy/src/main/java/ai/vespa/metricsproxy/http/ValuesFetcher.java
+++ b/metrics-proxy/src/main/java/ai/vespa/metricsproxy/http/ValuesFetcher.java
@@ -47,13 +47,14 @@ public class ValuesFetcher {
                 .collect(Collectors.toList());
     }
 
-    public List<MetricsPacket.Builder> fetchMetricsAsBuilders(String requestedConsumer) throws JsonRenderingException {
+    public MetricsPacket.Builder [] fetchMetricsAsBuilders(String requestedConsumer) throws JsonRenderingException {
         ConsumerId consumer = getConsumerOrDefault(requestedConsumer, metricsConsumers);
 
-        return metricsManager.getMetricsAsBuilders(vespaServices.getVespaServices(), Instant.now())
+        List<MetricsPacket.Builder> builders = metricsManager.getMetricsAsBuilders(vespaServices.getVespaServices(), Instant.now())
                 .stream()
                 .filter(builder -> builder.hasConsumer(consumer))
                 .collect(Collectors.toList());
+        return builders.toArray(new MetricsPacket.Builder[builders.size()]);
     }
 
 
diff --git a/metrics-proxy/src/main/java/ai/vespa/metricsproxy/http/metrics/MetricsV2Handler.java b/metrics-proxy/src/main/java/ai/vespa/metricsproxy/http/metrics/MetricsV2Handler.java
index eef5d9aaf98..f58c63cd76c 100644
--- a/metrics-proxy/src/main/java/ai/vespa/metricsproxy/http/metrics/MetricsV2Handler.java
+++ b/metrics-proxy/src/main/java/ai/vespa/metricsproxy/http/metrics/MetricsV2Handler.java
@@ -19,6 +19,7 @@ import com.yahoo.container.jdisc.HttpResponse;
 import com.yahoo.restapi.Path;
 
 import java.net.URI;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
@@ -66,8 +67,7 @@ public class MetricsV2Handler  extends HttpHandlerBase {
 
     private JsonResponse valuesResponse(String consumer) {
         try {
-            List<MetricsPacket.Builder> builders = valuesFetcher.fetchMetricsAsBuilders(consumer);
-            List<MetricsPacket> metrics = processAndBuild(builders,
+            List<MetricsPacket> metrics = processAndBuild(valuesFetcher.fetchMetricsAsBuilders(consumer),
                                                           new ServiceIdDimensionProcessor(),
                                                           new ClusterIdDimensionProcessor(),
                                                           new PublicDimensionsProcessor(MAX_DIMENSIONS));
@@ -81,12 +81,15 @@ public class MetricsV2Handler  extends HttpHandlerBase {
         }
     }
 
-    private static List<MetricsPacket> processAndBuild(List<MetricsPacket.Builder> builders,
+    private static List<MetricsPacket> processAndBuild(MetricsPacket.Builder [] builders,
                                                        MetricsProcessor... processors) {
-        return builders.stream()
-                .map(builder -> applyProcessors(builder, processors))
-                .map(MetricsPacket.Builder::build)
-                .collect(toList());
+        List<MetricsPacket> metricsPackets = new ArrayList<>(builders.length);
+        for (int i = 0; i < builders.length; i++) {
+            applyProcessors(builders[i], processors);
+            metricsPackets.add(builders[i].build());
+            builders[i] = null; // Set null to be able to GC the builder when packet has been created
+        }
+        return metricsPackets;
     }
 
 }
diff --git a/metrics-proxy/src/main/java/ai/vespa/metricsproxy/metric/model/MetricsPacket.java b/metrics-proxy/src/main/java/ai/vespa/metricsproxy/metric/model/MetricsPacket.java
index 02ccd2c988c..fff2302f98b 100644
--- a/metrics-proxy/src/main/java/ai/vespa/metricsproxy/metric/model/MetricsPacket.java
+++ b/metrics-proxy/src/main/java/ai/vespa/metricsproxy/metric/model/MetricsPacket.java
@@ -4,7 +4,6 @@ package ai.vespa.metricsproxy.metric.model;
 import ai.vespa.metricsproxy.metric.Metric;
 
 import java.time.Instant;
-import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.LinkedHashMap;
@@ -15,7 +14,6 @@ import java.util.Objects;
 import java.util.Set;
 import java.util.function.Function;
 
-import static java.util.Collections.unmodifiableList;
 import static java.util.Collections.unmodifiableMap;
 import static java.util.stream.Collectors.joining;
 
@@ -44,22 +42,14 @@ public class MetricsPacket {
         this.statusMessage = statusMessage;
         this.timestamp = timestamp;
         this.service = service;
-        this.metrics = metrics;
-        this.dimensions = dimensions;
+        this.metrics = Map.copyOf(metrics);
+        this.dimensions = unmodifiableMap(dimensions);
         this.consumers = Set.copyOf(consumers);
     }
 
-    public Map<MetricId, Number> metrics() {
-        return unmodifiableMap(metrics);
-    }
-
-    public Map<DimensionId, String> dimensions() {
-        return unmodifiableMap(dimensions);
-    }
-
-    public Set<ConsumerId> consumers() {
-        return consumers;
-    }
+    public Map<MetricId, Number> metrics() { return metrics; }
+    public Map<DimensionId, String> dimensions() { return dimensions; }
+    public Set<ConsumerId> consumers() { return consumers;}
 
     @Override
     public String toString() {