rdblue commented on a change in pull request #2945:
URL: https://github.com/apache/iceberg/pull/2945#discussion_r711403286



##########
File path: core/src/main/java/org/apache/iceberg/io/CDCWriter.java
##########
@@ -0,0 +1,135 @@
+/*
+ * 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.io;
+
+import java.io.IOException;
+import java.util.Map;
+import java.util.function.Function;
+import org.apache.iceberg.PartitionSpec;
+import org.apache.iceberg.Schema;
+import org.apache.iceberg.StructLike;
+import org.apache.iceberg.deletes.PositionDelete;
+import org.apache.iceberg.util.StructLikeMap;
+import org.apache.iceberg.util.StructProjection;
+
+public class CDCWriter<T> extends BaseDeltaWriter<T> {
+
+  private final FanoutDataWriter<T> dataWriter;
+  private final PartitionAwareFileWriter<T, DeleteWriteResult> 
equalityDeleteWriter;
+  private final PartitionAwareFileWriter<PositionDelete<T>, DeleteWriteResult> 
positionDeleteWriter;
+  private final StructProjection keyProjection;
+  private final Map<StructLike, PartitionAwarePathOffset> insertedRows;
+  private final PositionDelete<T> positionDelete;
+  private final Function<T, StructLike> toStructLike;
+
+  public CDCWriter(FanoutDataWriter<T> dataWriter,
+                   PartitionAwareFileWriter<T, DeleteWriteResult> 
equalityDeleteWriter,
+                   PartitionAwareFileWriter<PositionDelete<T>, 
DeleteWriteResult> positionDeleteWriter,
+                   Schema schema, Schema deleteSchema, Function<T, StructLike> 
toStructLike) {
+    this.dataWriter = dataWriter;
+    this.equalityDeleteWriter = equalityDeleteWriter;
+    this.positionDeleteWriter = positionDeleteWriter;
+    this.positionDelete = new PositionDelete<>();
+    this.keyProjection = StructProjection.create(schema, deleteSchema);
+    this.insertedRows = StructLikeMap.create(deleteSchema.asStruct());
+    this.toStructLike = toStructLike;
+  }
+
+  @Override
+  public void insert(T row, PartitionSpec spec, StructLike partition) throws 
IOException {
+    CharSequence currentPath = dataWriter.currentPath(spec, partition);
+    long currentPosition = dataWriter.currentPosition(spec, partition);
+    PartitionAwarePathOffset offset = new PartitionAwarePathOffset(spec, 
partition, currentPath, currentPosition);
+
+    StructLike copiedKey = 
StructCopy.copy(keyProjection.wrap(toStructLike.apply(row)));
+
+    PartitionAwarePathOffset previous = insertedRows.put(copiedKey, offset);
+    if (previous != null) {
+      // TODO: attach the previous row if has a position delete row schema
+      positionDelete.set(previous.path(), previous.rowOffset(), null);
+      positionDeleteWriter.write(positionDelete, spec, partition);
+    }
+
+    dataWriter.write(row, spec, partition);
+  }
+
+  @Override
+  public void delete(T row, PartitionSpec spec, StructLike partition) throws 
IOException {
+    StructLike key = keyProjection.wrap(toStructLike.apply(row));
+    PartitionAwarePathOffset previous = insertedRows.remove(key);
+    if (previous != null) {
+      // TODO: attach the previous row if has a position delete row schema
+      positionDelete.set(previous.path(), previous.rowOffset(), null);
+      positionDeleteWriter.write(positionDelete, previous.spec, 
previous.partition);
+    }
+
+    equalityDeleteWriter.write(row, spec, partition);
+  }
+
+  @Override
+  public void delete(CharSequence path, long pos, T row, PartitionSpec spec, 
StructLike partition) throws IOException {
+    throw new IllegalArgumentException(this.getClass().getName() + " does not 
implement explicit position delete");
+  }
+
+  @Override
+  protected void closeWriters() throws IOException {
+    if (dataWriter != null) {
+      closeDataWriter(dataWriter);
+    }
+
+    if (equalityDeleteWriter != null) {
+      closeDeleteWriter(equalityDeleteWriter);
+    }
+
+    if (positionDeleteWriter != null) {
+      closeDeleteWriter(positionDeleteWriter);
+    }
+  }
+
+  private static class PartitionAwarePathOffset {

Review comment:
       Could this extend `PositionDelete` so it can be passed directly into the 
delete writer?




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