Optimize IndexTemplateRegistry#clusterChanged (#115347) (#115366)

Author: joegallo

server/src/main/java/org/elasticsearch/cluster/metadata/ComposableIndexTemplate.java

@@ -28,6 +28,8 @@
 import org.elasticsearch.xcontent.XContentParser;
 
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -189,9 +191,14 @@ public List<String> getRequiredComponentTemplates() {
         if (ignoreMissingComponentTemplates == null) {
             return componentTemplates;
         }
-        return componentTemplates.stream()
-            .filter(componentTemplate -> ignoreMissingComponentTemplates.contains(componentTemplate) == false)
-            .toList();
+        // note: this loop is unrolled rather than streaming-style because it's hot enough to show up in a flamegraph
+        List<String> required = new ArrayList<>(componentTemplates.size());
+        for (String template : componentTemplates) {
+            if (ignoreMissingComponentTemplates.contains(template) == false) {
+                required.add(template);
+            }
+        }
+        return Collections.unmodifiableList(required);
     }
 
     @Nullable

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ilm/IndexLifecycleMetadata.java

@@ -25,6 +25,7 @@
 import java.io.IOException;
 import java.util.Collections;
 import java.util.EnumSet;
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
@@ -92,10 +93,13 @@ public OperationMode getOperationMode() {
     }
 
     public Map<String, LifecyclePolicy> getPolicies() {
-        return policyMetadatas.values()
-            .stream()
-            .map(LifecyclePolicyMetadata::getPolicy)
-            .collect(Collectors.toMap(LifecyclePolicy::getName, Function.identity()));
+        // note: this loop is unrolled rather than streaming-style because it's hot enough to show up in a flamegraph
+        Map<String, LifecyclePolicy> policies = new HashMap<>(policyMetadatas.size());
+        for (LifecyclePolicyMetadata policyMetadata : policyMetadatas.values()) {
+            LifecyclePolicy policy = policyMetadata.getPolicy();
+            policies.put(policy.getName(), policy);
+        }
+        return Collections.unmodifiableMap(policies);
     }
 
     @Override