platinumhamburg commented on code in PR #2105:
URL: https://github.com/apache/fluss/pull/2105#discussion_r2633500643


##########
fluss-common/src/main/java/org/apache/fluss/metadata/ChangelogImage.java:
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@@ -0,0 +1,59 @@
+/*
+ * 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.fluss.metadata;
+
+/**
+ * The changelog image mode for the primary key table.
+ *
+ * <p>This enum defines what information is included in the changelog for 
update operations. It is
+ * inspired by similar configurations in database systems like MySQL's 
binlog_row_image and
+ * PostgreSQL's replica identity.
+ *
+ * @since 0.9
+ */
+public enum ChangelogImage {
+
+    /**
+     * Full changelog with both UPDATE_BEFORE and UPDATE_AFTER records. This 
is the default behavior
+     * that captures complete information about updates, allowing tracking of 
previous values.
+     */
+    FULL,
+
+    /**
+     * WAL mode does not produce UPDATE_BEFORE records. Only INSERT, 
UPDATE_AFTER (and DELETE if
+     * allowed) records are emitted. When WAL mode is enabled with default 
merge engine (no merge
+     * engine configured) and full row updates (not partial update), an 
optimization is applied to
+     * skip looking up old values, and in this case INSERT operations are 
converted to UPDATE_AFTER
+     * events, similar to database WAL (Write-Ahead Log) behavior. This mode 
reduces storage and
+     * transmission costs but loses the ability to track previous values.
+     */
+    WAL;
+
+    /** Creates a {@link ChangelogImage} from the given string. */
+    public static ChangelogImage fromString(String image) {
+        switch (image.toUpperCase().replace("-", "_")) {

Review Comment:
   Sorry, this part is legacy code. In the legacy code, some enum names were 
kept with a “-”. I missed removing it during the refactor; I’ll delete it.



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