[GitHub] [iceberg] RussellSpitzer commented on a diff in pull request #7326: Spark 3.3: Output the net changes across snapshots in CDC

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

RussellSpitzer commented on code in PR #7326:
URL: https://github.com/apache/iceberg/pull/7326#discussion_r1164476406


##########
spark/v3.3/spark/src/main/java/org/apache/iceberg/spark/NetChangelogIterator.java:
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@@ -0,0 +1,138 @@
+/*
+ * 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.iceberg.spark;
+
+import java.util.Iterator;
+import org.apache.spark.sql.Row;
+import org.apache.spark.sql.types.StructType;
+
+public class NetChangelogIterator extends ChangelogIterator {
+
+  private Row firstRow = null;
+  private Row postImage = null;
+
+  protected NetChangelogIterator(
+      Iterator<Row> rowIterator, StructType rowType, String[] identifierFields) {
+    super(rowIterator, rowType, identifierFields);
+  }
+
+  @Override
+  public boolean hasNext() {
+    if (postImage != null || firstRow != null) {
+      return true;
+    }
+    return getRowIterator().hasNext();
+  }
+
+  /**
+   * This method iterates all versions of the same logical row across multiple snapshots. It caches
+   * the row's first version, and removes every version in between, then compares the last version
+   * with the first version to get the net change. Please note that it also removes any invalid
+   * data. For example, if there are two identical records, it will remove one of them.

Review Comment:
   I don't understand the example here. Why would we have two identical records in an invalid way?



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