openinx commented on a change in pull request #1663:
URL: https://github.com/apache/iceberg/pull/1663#discussion_r526813412



##########
File path: core/src/main/java/org/apache/iceberg/io/BaseDeltaWriter.java
##########
@@ -0,0 +1,248 @@
+/*
+ * 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.List;
+import java.util.function.Function;
+import org.apache.iceberg.DataFile;
+import org.apache.iceberg.DeleteFile;
+import org.apache.iceberg.Schema;
+import org.apache.iceberg.StructLike;
+import org.apache.iceberg.deletes.PositionDelete;
+import org.apache.iceberg.relocated.com.google.common.base.MoreObjects;
+import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
+import org.apache.iceberg.relocated.com.google.common.collect.Lists;
+import org.apache.iceberg.relocated.com.google.common.collect.Sets;
+import org.apache.iceberg.types.TypeUtil;
+import org.apache.iceberg.util.StructLikeMap;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class BaseDeltaWriter<T> implements DeltaWriter<T> {
+  private static final Logger LOG = 
LoggerFactory.getLogger(BaseDeltaWriter.class);
+
+  private final RollingContentFileWriter<DataFile, T> dataWriter;
+  private final RollingContentFileWriter<DeleteFile, T> equalityDeleteWriter;
+  private final RollingContentFileWriter<DeleteFile, PositionDelete<T>> 
posDeleteWriter;
+
+  private final PositionDelete<T> positionDelete = new PositionDelete<>();
+  private final StructLikeMap<List<FilePos>> insertedRowMap;
+
+  // Function to convert the generic data to a StructLike.
+  private final Function<T, StructLike> structLikeFun;
+
+  public BaseDeltaWriter(RollingContentFileWriter<DataFile, T> dataWriter) {
+    this(dataWriter, null);
+  }
+
+  public BaseDeltaWriter(RollingContentFileWriter<DataFile, T> dataWriter,
+                         RollingContentFileWriter<DeleteFile, 
PositionDelete<T>> posDeleteWriter) {
+    this(dataWriter, posDeleteWriter, null, null, null, null);
+  }
+
+  public BaseDeltaWriter(RollingContentFileWriter<DataFile, T> dataWriter,
+                         RollingContentFileWriter<DeleteFile, 
PositionDelete<T>> posDeleteWriter,
+                         RollingContentFileWriter<DeleteFile, T> 
equalityDeleteWriter,
+                         Schema tableSchema,
+                         List<Integer> equalityFieldIds,
+                         Function<T, StructLike> structLikeFun) {
+
+    Preconditions.checkNotNull(dataWriter, "Data writer should always not be 
null.");
+
+    if (posDeleteWriter == null) {
+      // Only accept INSERT records.
+      Preconditions.checkArgument(equalityDeleteWriter == null);
+    }
+
+    if (posDeleteWriter != null && equalityDeleteWriter == null) {
+      // Only accept INSERT records and position deletion.
+      Preconditions.checkArgument(tableSchema == null);
+      Preconditions.checkArgument(equalityFieldIds == null);
+    }
+
+    if (equalityDeleteWriter != null) {
+      // Accept insert records, position deletion, equality deletions.
+      Preconditions.checkNotNull(posDeleteWriter,
+          "Position delete writer shouldn't be null when writing equality 
deletions.");
+      Preconditions.checkNotNull(tableSchema, "Iceberg table schema shouldn't 
be null");
+      Preconditions.checkNotNull(equalityFieldIds, "Equality field ids 
shouldn't be null");
+      Preconditions.checkNotNull(structLikeFun, "StructLike function shouldn't 
be null");
+
+      Schema deleteSchema = TypeUtil.select(tableSchema, 
Sets.newHashSet(equalityFieldIds));
+      this.insertedRowMap = StructLikeMap.create(deleteSchema.asStruct());
+      this.structLikeFun = structLikeFun;
+    } else {
+      this.insertedRowMap = null;
+      this.structLikeFun = null;
+    }
+
+    this.dataWriter = dataWriter;
+    this.equalityDeleteWriter = equalityDeleteWriter;
+    this.posDeleteWriter = posDeleteWriter;
+  }
+
+  @Override
+  public void writeRow(T row) throws IOException {
+    if (enableEqualityDelete()) {
+      FilePos filePos = FilePos.create(dataWriter.currentPath(), 
dataWriter.currentPos());
+      insertedRowMap.compute(structLikeFun.apply(row), (k, v) -> {
+        if (v == null) {
+          return Lists.newArrayList(filePos);
+        } else {
+          v.add(filePos);
+          return v;

Review comment:
       Oh, there's another issue. Consider the two cases: 
   
   ```
   Case.1 : Execute two transactions: 
   
   txn1:  INSERT(1) ; DELETE(1); INSERT(1);
   txn2: INSERT(1) ; 
   ```
   
   It won't throw any duplicate key exception because we don't check the key 
existences cross transactions. 
   
   ```
   Case.2:  Execute only one transaction 
   
   txn1:    INSERT(1) ; INSERT(1); 
   ```
   
   we will encounter a `ValidationException` when executing the second 
`INSERT(1)`. 
   
   Will it confuse users because of the different behavior ? 
   
   For me,   iceberg won't check the key existence when inserting so in theory 
we don't have to guarantee that iceberg must throw a duplicated key exception 
if users really insert two duplicated records. 




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