Re: [PR] fix(debezium): keep Postgres toasted columns on MOR read (v6/v8) [hudi]

["hudi-agent (via GitHub)" <gi...@apache.org>]

hudi-agent commented on code in PR #19280:
URL: https://github.com/apache/hudi/pull/19280#discussion_r3575402067


##########
hudi-common/src/main/java/org/apache/hudi/common/model/debezium/PostgresDebeziumAvroPayload.java:
##########
@@ -96,22 +95,31 @@ public Option<IndexedRecord> combineAndGetUpdateValue(IndexedRecord currentValue
     Option<IndexedRecord> insertOrDeleteRecord = super.combineAndGetUpdateValue(currentValue, schema);
 
     if (insertOrDeleteRecord.isPresent()) {
-      mergeToastedValuesIfPresent(insertOrDeleteRecord.get(), currentValue);
+      return Option.of(mergeToastedValuesIfPresent(insertOrDeleteRecord.get(), currentValue));
     }
     return insertOrDeleteRecord;
   }
 
-  private void mergeToastedValuesIfPresent(IndexedRecord incomingRecord, IndexedRecord currentRecord) {
-    List<Schema.Field> fields = incomingRecord.getSchema().getFields();
-
-    fields.forEach(field -> {
+  /**
+   * Fills any TOASTed sentinel columns in {@code incomingRecord} with the value from
+   * {@code currentRecord}. Returns a NEW record when a fill occurs, so a caller (e.g. the record
+   * merger) does not mistake the result for the unchanged incoming record and discard the fill;
+   * returns {@code incomingRecord} unchanged when there is nothing to fill.
+   */
+  private IndexedRecord mergeToastedValuesIfPresent(IndexedRecord incomingRecord, IndexedRecord currentRecord) {
+    GenericData.Record filled = null;
+    for (Schema.Field field : incomingRecord.getSchema().getFields()) {
       // There are only four avro data types that have unconstrained sizes, which are
       // NON-NULLABLE STRING, NULLABLE STRING, NON-NULLABLE BYTES, NULLABLE BYTES
       if (((GenericRecord) incomingRecord).get(field.name()) != null
           && (containsStringToastedValues(incomingRecord, field) || containsBytesToastedValues(incomingRecord, field))) {
-        ((GenericRecord) incomingRecord).put(field.name(), ((GenericData.Record) currentRecord).get(field.name()));
+        if (filled == null) {
+          filled = new GenericData.Record((GenericData.Record) incomingRecord, false);

Review Comment:
   🤖 Could `incomingRecord` here ever be a `SerializableIndexedRecord` rather than a `GenericData.Record`? `BaseAvroPayload.getRecord()` returns a `SerializableIndexedRecord` when the stored record's schema isn't reference-equal to the requested schema, and in the avro file-group-reader path `AvroRecordContext.convertToAvroRecord` just casts `newer.getRecord()`. If so, `new GenericData.Record((GenericData.Record) incomingRecord, false)` would throw a ClassCastException on a toasted fill. The old in-place code used only the `GenericRecord` interface for STRING columns, so it was immune — building the copy from `incomingRecord.getSchema()` and copying via the interface might be safer.
   
   <sub><i>⚠️ AI-generated; verify before applying. React 👍/👎 to flag quality.</i></sub>



##########
hudi-spark-datasource/hudi-spark/src/test/scala/org/apache/hudi/functional/TestDebeziumToastedValue.scala:
##########
@@ -0,0 +1,116 @@
+/*
+ * 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.hudi.functional
+
+import org.apache.hudi.DataSourceWriteOptions
+import org.apache.hudi.DataSourceWriteOptions.{OPERATION, ORDERING_FIELDS, RECORDKEY_FIELD, TABLE_TYPE}
+import org.apache.hudi.common.config.HoodieMetadataConfig
+import org.apache.hudi.common.model.HoodieTableType
+import org.apache.hudi.common.model.debezium.{DebeziumConstants, PostgresDebeziumAvroPayload}
+import org.apache.hudi.common.table.HoodieTableMetaClient
+import org.apache.hudi.config.{HoodieCompactionConfig, HoodieWriteConfig}
+import org.apache.hudi.testutils.SparkClientFunctionalTestHarness
+
+import org.apache.spark.sql.SaveMode
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.params.ParameterizedTest
+import org.junit.jupiter.params.provider.ValueSource
+
+/**
+ * Functional test for [[PostgresDebeziumAvroPayload]]'s toasted / unavailable-value handling on a
+ * Merge-on-Read table.
+ *
+ * Postgres TOAST semantics: when a Debezium UPDATE cannot capture a large STRING/BYTES column that
+ * did not change, it ships the sentinel [[PostgresDebeziumAvroPayload.DEBEZIUM_TOASTED_VALUE]]
+ * (`__debezium_unavailable_value`) for that column. When the base file and delta log are merged at
+ * read time, such columns must KEEP the prior (base) value rather than be overwritten with the
+ * sentinel.
+ *
+ * Covers table versions 6, 8 and 9.
+ */
+class TestDebeziumToastedValue extends SparkClientFunctionalTestHarness {
+
+  private val sentinel = PostgresDebeziumAvroPayload.DEBEZIUM_TOASTED_VALUE
+  private val columns = Seq(
+    "id",
+    "name",
+    "city",
+    DebeziumConstants.FLATTENED_OP_COL_NAME,
+    DebeziumConstants.FLATTENED_LSN_COL_NAME)
+
+  @ParameterizedTest
+  @ValueSource(strings = Array("6", "8", "9"))
+  def testToastedColumnKeepsPriorValueOnRead(tableVersion: String): Unit = {
+    val opts = Map(
+      HoodieWriteConfig.WRITE_PAYLOAD_CLASS_NAME.key() -> classOf[PostgresDebeziumAvroPayload].getName,
+      HoodieMetadataConfig.ENABLE.key() -> "false",
+      // Preserve the table version across writes: disable auto-upgrade and pin the write version so
+      // a later write cannot migrate the table to a newer version mid-test.
+      HoodieWriteConfig.AUTO_UPGRADE_VERSION.key() -> "false",
+      HoodieWriteConfig.WRITE_TABLE_VERSION.key() -> tableVersion)
+
+    // 1. Base records at LSN 10.
+    val base = Seq(
+      (1, "alice", "NYC", "c", 10L),
+      (2, "bob", "LA", "c", 10L))
+    spark.createDataFrame(base).toDF(columns: _*).write.format("hudi")
+      .option(RECORDKEY_FIELD.key(), "id")
+      .option(ORDERING_FIELDS.key(), DebeziumConstants.FLATTENED_LSN_COL_NAME)
+      .option(TABLE_TYPE.key(), HoodieTableType.MERGE_ON_READ.name())
+      .option(DataSourceWriteOptions.TABLE_NAME.key(), "toasted_table")
+      .option(OPERATION.key(), DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL)
+      .option(HoodieCompactionConfig.INLINE_COMPACT.key(), "false")
+      .options(opts)
+      .mode(SaveMode.Overwrite)
+      .save(basePath)
+
+    // 2. Newer log records at LSN 20, each carrying the toasted sentinel in one column:
+    //    id=1 -> name updated, `city` toasted (must keep base "NYC")
+    //    id=2 -> name toasted (must keep base "bob"), `city` updated
+    val update = Seq(

Review Comment:
   🤖 nit: `val update` is a singular/verb form for what is actually a sequence of records — could you rename it to `val updates` or `val logRecords` to make it read as a collection?
   
   <sub><i>⚠️ AI-generated; verify before applying. React 👍/👎 to flag quality.</i></sub>



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