aokolnychyi commented on code in PR #55518:
URL: https://github.com/apache/spark/pull/55518#discussion_r3785130151


##########
sql/catalyst/src/main/java/org/apache/spark/sql/connector/write/SupportsColumnUpdates.java:
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@@ -0,0 +1,68 @@
+/*
+ * 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.spark.sql.connector.write;
+
+import org.apache.spark.annotation.Experimental;
+import org.apache.spark.sql.connector.expressions.NamedReference;
+
+/**
+ * A mix-in interface for {@link RowLevelOperation}. Data sources can 
implement this interface to
+ * receive a narrow row containing only the columns declared via {@link 
#requiredDataAttributes()}
+ * for updated, copied, and reinserted records, instead of the full table row.
+ * <p>
+ * Currently honored only for UPDATE. DELETE and MERGE ignore this interface: 
those operations
+ * receive full-width rows and {@link LogicalWriteInfo#updateSchema()} is 
absent for them.
+ *
+ * @since 4.3.0
+ */
+@Experimental
+public interface SupportsColumnUpdates extends RowLevelOperation {
+  /**
+   * Returns the data column references required to perform this row-level 
operation.
+   * <p>
+   * The returned columns become the schema of updated, copied, and reinserted 
rows, in declared
+   * order. Implementations must include every column they want to receive 
(typically the columns
+   * reported by {@link RowLevelOperationInfo#updatedColumns()} plus any 
columns needed for row
+   * lookup or routing, e.g. a primary key).
+   * <p>
+   * If any of the columns from {@link RowLevelOperationInfo#updatedColumns()} 
are
+   * missing, an analysis exception is thrown.
+   * <p>
+   * For updates on nested fields such as {@code SET t.s.c1 = -1} the 
connector should declare the
+   * root struct column {@code s} rather than any nested field.
+   */
+  NamedReference[] requiredDataAttributes();
+
+  /**
+   * Returns additional data column references that must be present in the 
narrow scan but are
+   * NOT delivered to the writer.
+   * <p>
+   * Use this for columns needed only for planning -- e.g. resolving the 
table's partitioning
+   * expressions against the scan output, or as clustering keys returned from
+   * {@link RequiresDistributionAndOrdering#requiredDistribution()} -- where 
the column itself
+   * should not appear in the row passed to
+   * {@link DataWriter#writeUpdate(Object, Object)} / {@link 
DeltaWriter#update} /
+   * {@link DeltaWriter#reinsert}. Columns returned here are not reflected in
+   * {@link LogicalWriteInfo#updateSchema()}.
+   * <p>
+   * Must not overlap with {@link #requiredDataAttributes()}; defaults to an 
empty array.
+   */
+  default NamedReference[] scanOnlyDataAttributes() {

Review Comment:
   Hmm.



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