update readMap to avoid resizing map during reading

docs/changelog/84045.yaml

@@ -0,0 +1,5 @@
+pr: 84045
+summary: Update `readMap` to avoid resizing map during reading
+area: Infra/Core
+type: enhancement
+issues: []

server/src/main/java/org/elasticsearch/common/io/stream/StreamInput.java

@@ -60,9 +60,7 @@
 import java.util.Collections;
 import java.util.Date;
 import java.util.EnumSet;
-import java.util.HashMap;
 import java.util.HashSet;
-import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Locale;
@@ -607,11 +605,11 @@ public String[] readOptionalStringArray() throws IOException {
      * If the returned map contains any entries it will be mutable. If it is empty it might be immutable.
      */
     public <K, V> Map<K, V> readMap(Writeable.Reader<K> keyReader, Writeable.Reader<V> valueReader) throws IOException {
-        return readMap(keyReader, valueReader, HashMap::new);
+        return readMap(keyReader, valueReader, Maps::newHashMapWithExpectedSize);
     }
 
     public <K, V> Map<K, V> readOrderedMap(Writeable.Reader<K> keyReader, Writeable.Reader<V> valueReader) throws IOException {
-        return readMap(keyReader, valueReader, LinkedHashMap::new);
+        return readMap(keyReader, valueReader, Maps::newLinkedHashMapWithExpectedSize);
     }
 
     private <K, V> Map<K, V> readMap(Writeable.Reader<K> keyReader, Writeable.Reader<V> valueReader, IntFunction<Map<K, V>> constructor)

server/src/main/java/org/elasticsearch/common/util/Maps.java

@@ -252,6 +252,18 @@ private static Map<String, Object> flatten(List<Object> list, boolean ordered, S
      * @return a new pre-sized {@link HashMap}
      */
     public static <K, V> Map<K, V> newMapWithExpectedSize(int expectedSize) {
+        return newHashMapWithExpectedSize(expectedSize);
+    }
+
+    /**
+     * Returns a hash map with a capacity sufficient to keep expectedSize elements without being resized.
+     *
+     * @param expectedSize the expected amount of elements in the map
+     * @param <K> the key type
+     * @param <V> the value type
+     * @return a new pre-sized {@link HashMap}
+     */
+    public static <K, V> Map<K, V> newHashMapWithExpectedSize(int expectedSize) {
         return new HashMap<>(capacity(expectedSize));
     }