[GitHub] [kafka] emissionnebula commented on a diff in pull request #13280: KAFKA-14735: Improve KRaft metadata image change performance at high …

["emissionnebula (via GitHub)" <gi...@apache.org>]

emissionnebula commented on code in PR #13280:
URL: https://github.com/apache/kafka/pull/13280#discussion_r1161315454


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server-common/src/main/java/org/apache/kafka/server/immutable/ImmutableMap.java:
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@@ -0,0 +1,47 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.kafka.server.immutable;
+
+import java.util.Map;
+
+/**
+ * A persistent Hash-based Map wrapper.
+ * java.util.Map methods that mutate in-place will throw UnsupportedOperationException
+ *
+ * @param <K> the key type
+ * @param <V> the value type
+ */
+public interface ImmutableMap<K, V> extends Map<K, V> {

Review Comment:
   +1



##########
server-common/src/main/java/org/apache/kafka/server/immutable/ImmutableMap.java:
##########
@@ -0,0 +1,47 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.kafka.server.immutable;
+
+import java.util.Map;
+
+/**
+ * A persistent Hash-based Map wrapper.
+ * java.util.Map methods that mutate in-place will throw UnsupportedOperationException
+ *
+ * @param <K> the key type
+ * @param <V> the value type
+ */
+public interface ImmutableMap<K, V> extends Map<K, V> {
+    /**
+     * @return the underlying persistent map
+     */
+    Object underlying();

Review Comment:
   Is there any need to expose the underlying object? Since we want to use only `ImmutableMap` and `java.util.Map` everywhere in the code, there would be no need to expose the underlying `PCollections` type from this interface. 



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