AnishMahto commented on code in PR #56283:
URL: https://github.com/apache/spark/pull/56283#discussion_r3364443540


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sql/pipelines/src/test/scala/org/apache/spark/sql/pipelines/autocdc/Scd2BatchProcessorSuite.scala:
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@@ -0,0 +1,1222 @@
+/*
+ * 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.pipelines.autocdc
+
+import org.apache.spark.sql.{functions => F, Column, QueryTest, Row}
+import org.apache.spark.sql.classic.DataFrame
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.test.SharedSparkSession
+import org.apache.spark.sql.types._
+
+class Scd2BatchProcessorSuite extends QueryTest with SharedSparkSession {
+
+  /** Build a microbatch [[DataFrame]] from explicit rows and an explicit 
schema. */
+  private def microbatchOf(schema: StructType)(rows: Row*): DataFrame =
+    spark.createDataFrame(spark.sparkContext.parallelize(rows), schema)
+
+  /**
+   * Build an aux-table [[DataFrame]] from explicit user rows + framework 
column values.
+   *
+   * TODO(SPARK-57265): switch to the production aux-schema helper once it 
lands, to avoid drift.
+   */
+  private def auxTableOf(
+      userSchema: StructType,
+      sequencingType: DataType = LongType
+  )(rows: Row*): DataFrame = {
+    val schema = userSchema
+      .add(Scd2BatchProcessor.startAtColName, sequencingType, nullable = true)
+      .add(Scd2BatchProcessor.endAtColName, sequencingType, nullable = true)
+      .add(
+        AutoCdcReservedNames.cdcMetadataColName,
+        Scd2BatchProcessor.cdcMetadataColSchema(sequencingType),
+        nullable = false
+      )
+      .add(Scd2BatchProcessor.deletedByBatchIdColName, LongType, nullable = 
true)
+    spark.createDataFrame(spark.sparkContext.parallelize(rows), schema)
+  }
+
+  /**
+   * Build a target-table [[DataFrame]] from explicit user rows + framework 
column values.
+   *
+   * Each input [[Row]] carries the user columns followed by:
+   *   - the row's `__START_AT` value
+   *   - the row's `__END_AT` value (null IFF the row is currently active)
+   *   - the row's `_cdc_metadata` struct as a [[Row]] (e.g., 
`Row(recordStartAt)`)
+   */
+  private def targetTableOf(
+      userSchema: StructType,
+      sequencingType: DataType = LongType
+  )(rows: Row*): DataFrame = {
+    val schema = userSchema
+      .add(Scd2BatchProcessor.startAtColName, sequencingType, nullable = true)
+      .add(Scd2BatchProcessor.endAtColName, sequencingType, nullable = true)
+      .add(
+        AutoCdcReservedNames.cdcMetadataColName,
+        Scd2BatchProcessor.cdcMetadataColSchema(sequencingType),
+        nullable = false
+      )
+    spark.createDataFrame(spark.sparkContext.parallelize(rows), schema)
+  }
+
+  /**
+   * Build a minimum-sequence-per-key [[DataFrame]] used by the 
`findAffected*` functions.
+   *
+   * Each input [[Row]] carries the key columns followed by the per-key 
minimum sequence.
+   */
+  private def minSeqOf(
+      keySchema: StructType,
+      sequencingType: DataType = LongType
+  )(rows: Row*): DataFrame = {
+    val schema = keySchema.add(
+      Scd2BatchProcessor.minSequenceColName,
+      sequencingType,
+      nullable = false
+    )
+    spark.createDataFrame(spark.sparkContext.parallelize(rows), schema)
+  }
+
+  /**
+   * Build a [[Scd2BatchProcessor]] suitable for `findAffected*` and
+   * `computeMinimumSequencePerKey` tests. The `sequencing` is fixed to 
`F.col("seq")`,
+   * so the input microbatch must include a `seq` column. `deleteCondition` is 
optional
+   * and only needed by tests that exercise both event kinds.
+   */
+  private def processorWithKeys(
+      keys: Seq[String],
+      deleteCondition: Option[Column] = None
+  ): Scd2BatchProcessor =
+    Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = keys.map(UnqualifiedColumnName(_)),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2,
+        deleteCondition = deleteCondition
+      ),
+      resolvedSequencingType = LongType
+    )
+
+  // =============== preprocessMicrobatch tests ===============
+
+  test("preprocessMicrobatch appends framework columns __START_AT, __END_AT, " 
+
+    "_cdc_metadata at the end of the schema in that order") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("value", StringType)
+
+    val batch = microbatchOf(schema)(Row(1, 10L, "a"))
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val result = processor.preprocessMicrobatch(batch)
+
+    assert(result.schema.fieldNames.toSeq == Seq(
+      "id", "seq", "value",
+      Scd2BatchProcessor.startAtColName,
+      Scd2BatchProcessor.endAtColName,
+      AutoCdcReservedNames.cdcMetadataColName
+    ))
+  }
+
+  test("preprocessMicrobatch returns an empty DataFrame with the full 
preprocessed schema") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("value", StringType)
+
+    val batch = microbatchOf(schema)()
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val result = processor.preprocessMicrobatch(batch)
+
+    assert(result.collect().isEmpty)
+    assert(result.schema.fieldNames.toSeq == Seq(
+      "id", "seq", "value",
+      Scd2BatchProcessor.startAtColName,
+      Scd2BatchProcessor.endAtColName,
+      AutoCdcReservedNames.cdcMetadataColName
+    ))
+  }
+
+  test("preprocessMicrobatch stamps __START_AT, __END_AT, and 
__RECORD_START_AT correctly " +
+    "across delete and upsert events for the same key") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("value", StringType)
+      .add("is_delete", BooleanType)
+
+    // All three events target the same key. SCD2 must preserve every event in 
the output -
+    // unlike SCD1, no per-key deduplication is performed; this also 
implicitly pins the
+    // no-dedup contract of preprocessMicrobatch.
+    val batch = microbatchOf(schema)(
+      Row(1, 10L, "first-upsert", false),
+      Row(1, 20L, "second-upsert", false),
+      Row(1, 30L, null, true)
+    )
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2,
+        deleteCondition = Some(F.col("is_delete"))
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    // Per-row contract for the framework columns:
+    //   - __START_AT      = sequencing for every row (the active-from time)
+    //   - __END_AT        = sequencing for delete rows; null for upserts 
(mutual exclusion)
+    //   - __RECORD_START_AT = sequencing for every row, regardless of delete 
vs upsert
+    //                        (lineage preserved into the merge step)
+    checkAnswer(
+      df = processor.preprocessMicrobatch(batch),
+      expectedAnswer = Seq(
+        Row(1, 10L, "first-upsert", false, 10L, null, Row(10L)),
+        Row(1, 20L, "second-upsert", false, 20L, null, Row(20L)),
+        Row(1, 30L, null, true, 30L, 30L, Row(30L))
+      )
+    )
+  }
+
+  test("preprocessMicrobatch preserves byte-identical full-event duplicates") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("value", StringType)
+      .add("is_delete", BooleanType)
+
+    // Two byte-identical events for the same key: same key, same sequencing, 
same data, same
+    // delete flag. SCD2 preprocessing intentionally preserves every event 
verbatim, including
+    // full-event duplicates. Cross-event redundancy elimination (collapsing 
duplicates before
+    // they could reconcile to a zero-width visible row) is the responsibility 
of downstream
+    // reconciliation, not preprocessing.
+    val batch = microbatchOf(schema)(
+      Row(1, 10L, "alice", false),
+      Row(1, 10L, "alice", false)
+    )
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2,
+        deleteCondition = Some(F.col("is_delete"))
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    // Both rows must survive verbatim.
+    checkAnswer(
+      df = processor.preprocessMicrobatch(batch),
+      expectedAnswer = Seq(
+        Row(1, 10L, "alice", false, 10L, null, Row(10L)),
+        Row(1, 10L, "alice", false, 10L, null, Row(10L))
+      )
+    )
+  }
+
+  test("preprocessMicrobatch leaves __END_AT null on every row when 
deleteCondition is None") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("value", StringType)
+
+    val batch = microbatchOf(schema)(
+      Row(1, 10L, "a"),
+      Row(2, 20L, "b")
+    )
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2,
+        deleteCondition = None
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    checkAnswer(
+      df = processor.preprocessMicrobatch(batch).select(
+        F.col(Scd2BatchProcessor.endAtColName)
+      ),
+      expectedAnswer = Seq(Row(null), Row(null))
+    )
+  }
+
+  test("preprocessMicrobatch treats null deleteCondition results as upsert " +
+    "(__END_AT stays null)") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("is_delete", BooleanType)
+
+    val batch = microbatchOf(schema)(
+      // is_delete is null - the delete condition evaluates to null, which 
Spark treats as the
+      // otherwise branch, so the row is classified as an upsert.
+      Row(1, 10L, null)
+    )
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2,
+        deleteCondition = Some(F.col("is_delete"))
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    checkAnswer(
+      df = processor.preprocessMicrobatch(batch).select(
+        F.col(Scd2BatchProcessor.endAtColName)
+      ),
+      expectedAnswer = Row(null)
+    )
+  }
+
+  test("preprocessMicrobatch evaluates an arbitrary sequencing expression 
per-row") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("alt_seq", LongType)
+      .add("value", StringType)
+
+    // Sequencing is a function call referencing multiple columns, not a bare 
identifier. Locks
+    // in that the framework columns evaluate the full expression per-row 
rather than treating
+    // `sequencing` as a single column reference.
+    val batch = microbatchOf(schema)(
+      // greatest(10, 30) = 30
+      Row(1, 10L, 30L, "row1"),
+      // greatest(40, 20) = 40
+      Row(2, 40L, 20L, "row2")
+    )
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.greatest(F.col("seq"), F.col("alt_seq")),
+        storedAsScdType = ScdType.Type2
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val result = processor.preprocessMicrobatch(batch)
+
+    checkAnswer(
+      df = result.select(
+        F.col(Scd2BatchProcessor.startAtColName),
+        F.col(s"${AutoCdcReservedNames.cdcMetadataColName}." +
+          s"${Scd2BatchProcessor.recordStartAtFieldName}")
+      ),
+      expectedAnswer = Seq(
+        Row(30L, 30L),
+        Row(40L, 40L)
+      )
+    )
+  }
+
+  /** Schema reused by columnSelection tests: id (key), name, age, seq 
(sequencing). */
+  private val multiUserColSchema: StructType = new StructType()
+    .add("id", IntegerType)
+    .add("name", StringType)
+    .add("age", IntegerType)
+    .add("seq", LongType)
+
+  test("preprocessMicrobatch keeps every user column when columnSelection is 
None") {
+    val batch = microbatchOf(multiUserColSchema)(
+      Row(1, "alice", 30, 10L)
+    )
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2,
+        columnSelection = None
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val result = processor.preprocessMicrobatch(batch)
+
+    assert(result.schema.fieldNames.toSeq == Seq(
+      "id", "name", "age", "seq",
+      Scd2BatchProcessor.startAtColName,
+      Scd2BatchProcessor.endAtColName,
+      AutoCdcReservedNames.cdcMetadataColName
+    ))
+  }
+
+  test("preprocessMicrobatch retains framework columns even when 
IncludeColumns omits them") {
+    val batch = microbatchOf(multiUserColSchema)(
+      Row(1, "alice", 30, 10L)
+    )
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2,
+        columnSelection = Some(ColumnSelection.IncludeColumns(
+          Seq(UnqualifiedColumnName("id"), UnqualifiedColumnName("age"))
+        ))
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val result = processor.preprocessMicrobatch(batch)
+
+    assert(result.schema.fieldNames.toSeq == Seq(
+      "id", "age",
+      Scd2BatchProcessor.startAtColName,
+      Scd2BatchProcessor.endAtColName,
+      AutoCdcReservedNames.cdcMetadataColName
+    ))
+    checkAnswer(
+      df = result,
+      expectedAnswer = Row(1, 30, 10L, null, Row(10L))
+    )
+  }
+
+  test("preprocessMicrobatch drops user columns listed in ExcludeColumns; " +
+    "framework columns survive") {
+    val batch = microbatchOf(multiUserColSchema)(
+      Row(1, "alice", 30, 10L)
+    )
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2,
+        columnSelection = Some(ColumnSelection.ExcludeColumns(
+          Seq(UnqualifiedColumnName("name"))
+        ))
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val result = processor.preprocessMicrobatch(batch)
+
+    assert(result.schema.fieldNames.toSeq == Seq(
+      "id", "age", "seq",
+      Scd2BatchProcessor.startAtColName,
+      Scd2BatchProcessor.endAtColName,
+      AutoCdcReservedNames.cdcMetadataColName
+    ))
+    checkAnswer(
+      df = result,
+      expectedAnswer = Row(1, 30, 10L, 10L, null, Row(10L))
+    )
+  }
+
+  test("preprocessMicrobatch preserves the microbatch schema's user-column 
order, " +
+    "ignoring the order of IncludeColumns") {
+    val batch = microbatchOf(multiUserColSchema)(
+      Row(1, "alice", 30, 10L)
+    )
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2,
+        // User specifies (age, id) - intentionally different from the schema 
order (id, age).
+        columnSelection = Some(ColumnSelection.IncludeColumns(
+          Seq(UnqualifiedColumnName("age"), UnqualifiedColumnName("id"))
+        ))
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val result = processor.preprocessMicrobatch(batch)
+
+    // Output column order follows the microbatch schema (id before age), not 
the user's listing
+    // order in IncludeColumns. Framework columns are always appended last.
+    assert(result.schema.fieldNames.toSeq == Seq(
+      "id", "age",
+      Scd2BatchProcessor.startAtColName,
+      Scd2BatchProcessor.endAtColName,
+      AutoCdcReservedNames.cdcMetadataColName
+    ))
+  }
+
+  test("preprocessMicrobatch resolves columnSelection case-insensitively " +
+    "when SQLConf.CASE_SENSITIVE=false") {
+    withSQLConf(SQLConf.CASE_SENSITIVE.key -> "false") {
+      val batch = microbatchOf(multiUserColSchema)(
+        Row(1, "alice", 30, 10L)
+      )
+
+      val processor = Scd2BatchProcessor(
+        changeArgs = ChangeArgs(
+          keys = Seq(UnqualifiedColumnName("id")),
+          sequencing = F.col("seq"),
+          storedAsScdType = ScdType.Type2,
+          // User columns intentionally use a different case than the schema 
(id, age).
+          columnSelection = Some(ColumnSelection.IncludeColumns(
+            Seq(UnqualifiedColumnName("ID"), UnqualifiedColumnName("AGE"))
+          ))
+        ),
+        resolvedSequencingType = LongType
+      )
+
+      val result = processor.preprocessMicrobatch(batch)
+
+      // Output column names follow the microbatch schema's casing, not the 
user's casing.
+      assert(result.schema.fieldNames.toSeq == Seq(
+        "id", "age",
+        Scd2BatchProcessor.startAtColName,
+        Scd2BatchProcessor.endAtColName,
+        AutoCdcReservedNames.cdcMetadataColName
+      ))
+    }
+  }
+
+  test("preprocessMicrobatch handles backticked column names containing a 
literal dot") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      // Even if a column is created with backticks via DDL, those backticks 
are consumed by Spark
+      // before resolving the schema; they won't show up in the schema field.
+      .add("user.id", StringType)
+      .add("seq", LongType)
+
+    val batch = microbatchOf(schema)(
+      Row(1, "u-100", 10L)
+    )
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2,
+        columnSelection = Some(ColumnSelection.IncludeColumns(
+          Seq(
+            UnqualifiedColumnName("id"),
+            UnqualifiedColumnName("`user.id`")
+          )
+        ))
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val result = processor.preprocessMicrobatch(batch)
+
+    assert(result.schema.fieldNames.toSeq == Seq(
+      "id", "user.id",
+      Scd2BatchProcessor.startAtColName,
+      Scd2BatchProcessor.endAtColName,
+      AutoCdcReservedNames.cdcMetadataColName
+    ))
+    checkAnswer(
+      df = result,
+      expectedAnswer = Row(1, "u-100", 10L, null, Row(10L))
+    )
+  }
+
+  test("preprocessMicrobatch correctly populates framework columns even when 
ExcludeColumns " +
+    "drops the columns referenced by sequencing and deleteCondition") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("value", StringType)
+      // Both seq and is_delete are referenced by the flow's sequencing / 
deleteCondition
+      // expressions, but the user wants them excluded from the target table.
+      .add("seq", LongType)
+      .add("is_delete", BooleanType)
+
+    val batch = microbatchOf(schema)(
+      Row(1, "alice", 10L, false),
+      Row(1, null, 20L, true)
+    )
+
+    val processor = Scd2BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type2,
+        deleteCondition = Some(F.col("is_delete")),
+        columnSelection = Some(ColumnSelection.ExcludeColumns(
+          Seq(UnqualifiedColumnName("seq"), UnqualifiedColumnName("is_delete"))
+        ))
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    // The orchestrator runs row-extension steps before column selection, so 
the framework
+    // columns reference seq / is_delete fully even though the final 
projection drops them.
+    val result = processor.preprocessMicrobatch(batch)
+
+    assert(result.schema.fieldNames.toSeq == Seq(
+      "id", "value",
+      Scd2BatchProcessor.startAtColName,
+      Scd2BatchProcessor.endAtColName,
+      AutoCdcReservedNames.cdcMetadataColName
+    ))
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(
+        Row(1, "alice", 10L, null, Row(10L)),
+        Row(1, null, 20L, 20L, Row(20L))
+      )
+    )
+  }
+
+  // =============== computeMinimumSequencePerKey tests ===============
+
+  test("computeMinimumSequencePerKey returns one row per distinct key and 
aggregates across " +
+    "both upsert and delete events") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("is_delete", BooleanType)
+
+    val processor = processorWithKeys(
+      keys = Seq("id"),
+      deleteCondition = Some(F.col("is_delete"))
+    )
+
+    // Two keys, each with multiple events including at least one delete and 
at least one
+    // out-of-order sequence. Delete events must feed into the per-key min 
exactly like
+    // upserts: `preprocessMicrobatch` stamps `__RECORD_START_AT = sequencing` 
on every
+    // row regardless of kind, so the min computation cannot legitimately 
ignore deletes.
+    // (If it did, the early-delete-bisects-late-upsert reconciliation case 
would silently
+    // lose its anchor pull-in via the find* paths.)
+    val raw = microbatchOf(schema)(
+      Row(1, 30L, false),  // out-of-order: appears before lower sequences in 
the input
+      Row(1, 10L, true),   // delete - smallest sequence for key=1
+      Row(1, 20L, false),
+      Row(2, 50L, false),
+      Row(2, 40L, true)    // delete - smallest sequence for key=2
+    )
+
+    val preprocessed = processor.preprocessMicrobatch(raw)
+    val result = processor.computeMinimumSequencePerKey(preprocessed)
+
+    assert(result.schema.fieldNames.toSeq == Seq(
+      "id", Scd2BatchProcessor.minSequenceColName
+    ))
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(
+        Row(1, 10L),
+        Row(2, 40L)
+      )
+    )
+  }
+
+  test("computeMinimumSequencePerKey is compatible with composite keys") {
+    val schema = new StructType()
+      .add("region", StringType)
+      .add("customer_id", IntegerType)
+      .add("seq", LongType)
+
+    val processor = processorWithKeys(keys = Seq("region", "customer_id"))
+
+    // Three composite-key tuples that share their first or second key column. 
If the
+    // function mistakenly grouped by `region` alone, (US, 1) and (US, 2) 
would collapse
+    // and we'd see only two output rows; if it grouped by `customer_id` alone,
+    // (US, 1) and (EU, 1) would collapse.
+    val raw = microbatchOf(schema)(
+      Row("US", 1, 100L),
+      Row("US", 1,  50L),  // smaller sequence for (US, 1)
+      Row("US", 2, 200L),
+      Row("EU", 1,  30L)
+    )
+
+    val preprocessed = processor.preprocessMicrobatch(raw)
+    val result = processor.computeMinimumSequencePerKey(preprocessed)
+
+    assert(result.schema.fieldNames.toSeq == Seq(
+      "region", "customer_id", Scd2BatchProcessor.minSequenceColName
+    ))
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(
+        Row("US", 1,  50L),
+        Row("US", 2, 200L),
+        Row("EU", 1,  30L)
+      )
+    )
+  }
+
+  test("computeMinimumSequencePerKey returns an empty result for an empty 
microbatch") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+
+    val processor = processorWithKeys(keys = Seq("id"))
+
+    val raw = microbatchOf(schema)()
+    val preprocessed = processor.preprocessMicrobatch(raw)
+    val result = processor.computeMinimumSequencePerKey(preprocessed)
+
+    assert(result.collect().isEmpty)
+  }
+
+  test("computeMinimumSequencePerKey resolves key columns containing a literal 
dot") {
+    // Symmetric to the dotted-name test for 
findAffectedRowsFromAuxiliaryTable: the
+    // `groupBy(keysQuoted.map(F.col): _*)` site relies on `keysQuoted` 
correctly
+    // backtick-quoting "a.b" so that F.col parses it as a literal column name 
(rather
+    // than struct-field access). Pins the F.col axis of the keysQuoted vs 
keysRaw split.
+    val schema = new StructType()
+      .add("a.b", IntegerType)
+      .add("seq", LongType)
+
+    val processor = processorWithKeys(keys = Seq("`a.b`"))
+
+    val raw = microbatchOf(schema)(
+      Row(1, 30L),
+      Row(1, 10L)
+    )
+    val preprocessed = processor.preprocessMicrobatch(raw)
+    val result = processor.computeMinimumSequencePerKey(preprocessed)
+
+    assert(result.schema.fieldNames.toSeq == Seq(
+      "a.b", Scd2BatchProcessor.minSequenceColName
+    ))
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(Row(1, 10L))
+    )
+  }
+
+  // =============== findAffectedRowsFromAuxiliaryTable tests ===============
+
+  test("findAffectedRowsFromAuxiliaryTable returns the anchor row per key") {
+    val processor = processorWithKeys(Seq("id"))
+    val keySchema = new StructType().add("id", IntegerType)
+    val userSchema = keySchema.add("value", StringType)
+
+    // Two keys to demonstrate per-key anchor isolation.
+    //
+    // Input row shape per `auxTableOf`:
+    //   (id, value, __START_AT, __END_AT, Row(recordStartAt), 
deletedByBatchId)
+    //
+    // Key 1: aux rows at recordStartAt 3, 5, 10. minSeq = 10.
+    //   - 3  -> older than the anchor; dropped.
+    //   - 5  -> anchor (max < 10); included.
+    //   - 10 -> at minSeq; included via the >= branch (NOT as anchor; 
selection is strict <).
+    // Key 2: only one aux row at 7, minSeq = 7.
+    //   - 7  -> at minSeq; included via >= branch. No anchor (no rows < 7 for 
this key).
+    val aux = auxTableOf(userSchema)(
+      Row(1, "v1.3",  3L,  null, Row(3L),  null),
+      Row(1, "v1.5",  5L,  null, Row(5L),  null),
+      Row(1, "v1.10", 10L, null, Row(10L), null),
+      Row(2, "v2.7",  7L,  null, Row(7L),  null)
+    )
+    val minSeq = minSeqOf(keySchema)(
+      Row(1, 10L),
+      Row(2, 7L)
+    )
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = 100L
+    )
+
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(
+        Row(1, "v1.5",  5L,  null, Row(5L)),    // anchor for key=1
+        Row(1, "v1.10", 10L, null, Row(10L)),   // >= minSeq for key=1
+        Row(2, "v2.7",  7L,  null, Row(7L))     // >= minSeq for key=2 (no 
anchor)
+      )
+    )
+  }
+
+  test("findAffectedRowsFromAuxiliaryTable pulls in both tombstone and no-op 
upsert rows") {
+    val processor = processorWithKeys(Seq("id"))
+    val keySchema = new StructType().add("id", IntegerType)
+    val userSchema = keySchema.add("value", StringType)
+
+    // Aux carries a mix of row kinds for one key. The find function does NOT 
distinguish
+    // between them - it filters purely on `recordStartAt` - so a tombstone, a 
no-op upsert
+    // run head, and a continuation are all eligible anchor candidates and all 
eligible for
+    // the >= minSeq inclusion branch.
+    val aux = auxTableOf(userSchema)(
+      // Tombstone at recordStartAt = 3 (deleted at sequence 3): startAt = 
endAt = 3.
+      // Older than the anchor; dropped.
+      Row(1, null,    3L, 3L,   Row(3L),  null),
+      // No-op upsert continuation at recordStartAt = 7: startAt inherits its 
run head's
+      // recordStartAt, endAt is null. Anchor for minSeq=10 (max < 10).
+      Row(1, "alice", 5L, null, Row(7L),  null),
+      // Tombstone at recordStartAt = 12: at-or-after minSeq, included via >= 
branch.
+      Row(1, null,    12L, 12L, Row(12L), null),
+      // No-op upsert continuation at recordStartAt = 15: included via >= 
branch.
+      Row(1, "bob",   13L, null, Row(15L), null)
+    )
+    val minSeq = minSeqOf(keySchema)(Row(1, 10L))
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = 100L
+    )
+
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(
+        Row(1, "alice", 5L,  null, Row(7L)),
+        Row(1, null,    12L, 12L,  Row(12L)),
+        Row(1, "bob",   13L, null, Row(15L))
+      )
+    )
+  }
+
+  test("findAffectedRowsFromAuxiliaryTable pulls in both consecutive no-op 
upsert events " +
+    "being interleaved by incoming microbatch row") {
+    val processor = processorWithKeys(Seq("id"))
+    val keySchema = new StructType().add("id", IntegerType)
+    val userSchema = keySchema.add("value", StringType)
+
+    val aux = auxTableOf(userSchema)(
+      Row(1, "alice", 2L, null, Row(8L),  null),
+      Row(1, "alice", 2L, null, Row(12L), null)
+    )
+    val minSeq = minSeqOf(keySchema)(Row(1, 10L))
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = 100L
+    )
+
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(
+        // Row with record start at of 8 gets pulled in as an anchor,
+        Row(1, "alice", 2L, null, Row(8L)),
+        // Row with record start at of 12 gets pulled in as a regular affected 
row.
+        Row(1, "alice", 2L, null, Row(12L))
+      )
+    )
+  }
+
+  test("findAffectedRowsFromAuxiliaryTable selects tombstones as anchor if 
applicable") {
+    val processor = processorWithKeys(Seq("id"))
+    val keySchema = new StructType().add("id", IntegerType)
+    val userSchema = keySchema.add("value", StringType)
+
+    // Tombstone-as-anchor is incidental: the find function selects the anchor 
purely on
+    // `max recordStartAt < minSeq`, so a tombstone qualifies just like any 
other row kind.
+    // Downstream reconciliation does not actually rely on the anchor when it 
is a
+    // tombstone (a delete already closed the prior run, so any subsequent 
incoming event
+    // is necessarily a fresh run head regardless of whether the anchor is 
surfaced). We
+    // still pull it in as a harmless side effect of the range filter, and 
this behavior is
+    // documented via test.
+    val aux = auxTableOf(userSchema)(
+      Row(1, null, 7L,  7L,  Row(7L),  null),
+      Row(1, null, 12L, 12L, Row(12L), null)
+    )
+    val minSeq = minSeqOf(keySchema)(Row(1, 10L))
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = 100L
+    )
+
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(
+        // Pulled in as anchor.
+        Row(1, null, 7L,  7L,  Row(7L)),
+        // Pulled in as regular affected row.
+        Row(1, null, 12L, 12L, Row(12L))
+      )
+    )
+  }
+
+  test("findAffectedRowsFromAuxiliaryTable filters logically-deleted aux 
rows") {
+    val processor = processorWithKeys(Seq("id"))
+    val keySchema = new StructType().add("id", IntegerType)
+    val userSchema = keySchema.add("value", StringType)
+
+    val currentBatchId = 100L
+    val differentBatchId = 99L
+
+    // The idempotency filter retains rows deleted by `currentBatchId` (so a 
mid-flight
+    // retry sees its own prior writes) and drops rows deleted by any other 
batch. This
+    // applies uniformly to both the anchor and non-anchor affected rows.
+    val aux = auxTableOf(userSchema)(
+      // Anchor candidate (recordStartAt < minSeq):
+      Row(1, "anchor",  5L,  null, Row(5L),  currentBatchId),    // deleted by 
current -> kept
+      // At-or-after minSeq:
+      Row(1, "live",    10L, null, Row(10L), null),              // not 
deleted -> kept
+      Row(1, "retried", 11L, null, Row(11L), currentBatchId),    // deleted by 
current -> kept
+      Row(1, "ignored", 12L, null, Row(12L), differentBatchId)   // deleted by 
another -> dropped
+    )
+    val minSeq = minSeqOf(keySchema)(Row(1, 10L))
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = currentBatchId
+    )
+
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(
+        Row(1, "anchor",  5L,  null, Row(5L)),
+        Row(1, "live",    10L, null, Row(10L)),
+        Row(1, "retried", 11L, null, Row(11L))
+      )
+    )
+  }
+
+  test("findAffectedRowsFromAuxiliaryTable falls back to the next anchor when 
the closest " +
+    "candidate was logically deleted by a different batch") {
+    val processor = processorWithKeys(Seq("id"))
+    val keySchema = new StructType().add("id", IntegerType)
+    val userSchema = keySchema.add("value", StringType)
+
+    val currentBatchId = 100L
+    val differentBatchId = 99L
+
+    // Codifies the step-ordering invariant inside 
`findAffectedRowsFromAuxiliaryTable`: the
+    // idempotency filter MUST run before the anchor `max(...)` aggregation. 
Here the closest
+    // pre-minSeq candidate (recordStartAt=7) was logically deleted by a 
different batch, so
+    // it is filtered out and the anchor falls back to recordStartAt=3. If a 
future refactor
+    // were to flip these two steps (e.g. as a "perf optimization"), this test 
would catch it
+    // because the natural-anchor row (7) would otherwise be selected and then 
dropped, leaving
+    // no anchor at all.
+    val aux = auxTableOf(userSchema)(
+      Row(1, "live3",  3L, null, Row(3L), null),
+      Row(1, "stale7", 7L, null, Row(7L), differentBatchId)
+    )
+    val minSeq = minSeqOf(keySchema)(Row(1, 10L))
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = currentBatchId
+    )
+
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(Row(1, "live3", 3L, null, Row(3L)))
+    )
+  }
+
+  test("findAffectedRowsFromAuxiliaryTable drops the aux-only deletedByBatchId 
column") {
+    val processor = processorWithKeys(Seq("id"))
+    val keySchema = new StructType().add("id", IntegerType)
+    val userSchema = keySchema.add("value", StringType)
+
+    // Pre-condition: aux carries the canonical SCD2 row schema plus the 
top-level
+    // `__spark_autocdc_deleted_by_batch_id` idempotency column. The find 
function must
+    // drop that aux-only column so the result is union-compatible with 
target-table rows
+    // and preprocessed-microbatch rows downstream, while leaving the 
(now-shared)
+    // `_cdc_metadata` struct schema untouched.
+    val aux = auxTableOf(userSchema)(Row(1, "v", 5L, null, Row(5L), null))
+    val minSeq = minSeqOf(keySchema)(Row(1, 10L))
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = 100L
+    )
+
+    
assert(!result.columns.contains(Scd2BatchProcessor.deletedByBatchIdColName))
+    val cdcMetadataField = 
result.schema(AutoCdcReservedNames.cdcMetadataColName)
+    assert(cdcMetadataField.dataType == 
Scd2BatchProcessor.cdcMetadataColSchema(LongType))
+  }
+
+  test("findAffectedRowsFromAuxiliaryTable resolves key columns containing a 
literal dot") {
+    val processor = processorWithKeys(Seq("`a.b`"))
+    val keySchema = new StructType().add("a.b", IntegerType)
+    val userSchema = keySchema.add("value", StringType)
+
+    val aux = auxTableOf(userSchema)(Row(1, "v", 5L, null, Row(5L), null))
+    val minSeq = minSeqOf(keySchema)(Row(1, 10L))
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = 100L
+    )
+
+    // The lone aux row is the anchor (recordStartAt=5 < minSeq=10, no other 
candidates).
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(Row(1, "v", 5L, null, Row(5L)))
+    )
+  }
+
+  test("findAffectedRowsFromAuxiliaryTable respects composite keys") {
+    val keySchema = new StructType()
+      .add("region", StringType)
+      .add("customer_id", IntegerType)
+    val userSchema = keySchema.add("name", StringType)
+
+    val processor = processorWithKeys(Seq("region", "customer_id"))
+
+    // Three composite keys: (US, 1), (EU, 1), (US, 2). Each is independent.
+    //   (US, 1): anchor at 3; row at 10 included via >=.
+    //   (EU, 1): anchor at 4; no rows at or after 12 -> only the anchor.
+    //   (US, 2): no aux rows -> contributes nothing.
+    val aux = auxTableOf(userSchema)(
+      Row("US", 1, "us1.3",  3L,  null, Row(3L),  null),
+      Row("US", 1, "us1.10", 10L, null, Row(10L), null),
+      Row("EU", 1, "eu1.4",  4L,  null, Row(4L),  null)
+    )
+    val minSeq = minSeqOf(keySchema)(
+      Row("US", 1, 10L),
+      Row("EU", 1, 12L),
+      Row("US", 2, 100L)
+    )
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = 100L
+    )
+
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(
+        Row("US", 1, "us1.3",  3L,  null, Row(3L)),
+        Row("US", 1, "us1.10", 10L, null, Row(10L)),
+        Row("EU", 1, "eu1.4",  4L,  null, Row(4L))
+      )
+    )
+  }
+
+  test("findAffectedRowsFromAuxiliaryTable returns an empty result when the 
aux table is empty") {
+    val processor = processorWithKeys(Seq("id"))
+    val keySchema = new StructType().add("id", IntegerType)
+    val userSchema = keySchema.add("value", StringType)
+
+    val aux = auxTableOf(userSchema)()
+    val minSeq = minSeqOf(keySchema)(Row(1, 10L))
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = 100L
+    )
+
+    assert(result.collect().isEmpty)
+  }
+
+  test("findAffectedRowsFromAuxiliaryTable returns no rows for a microbatch 
key that has " +
+    "no rows in the aux table") {
+    val processor = processorWithKeys(Seq("id"))
+    val keySchema = new StructType().add("id", IntegerType)
+    val userSchema = keySchema.add("value", StringType)
+
+    // Aux only has rows for key=1. Microbatch only sees key=2.
+    val aux = auxTableOf(userSchema)(Row(1, "v", 5L, null, Row(5L), null))
+    val minSeq = minSeqOf(keySchema)(Row(2, 10L))
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = 100L
+    )
+
+    assert(result.collect().isEmpty)
+  }
+
+  test("findAffectedRowsFromAuxiliaryTable excludes aux rows for keys not in 
the microbatch") {
+    val processor = processorWithKeys(Seq("id"))
+    val keySchema = new StructType().add("id", IntegerType)
+    val userSchema = keySchema.add("value", StringType)
+
+    // Aux has rows for keys 1 and 2. Microbatch only mentions key=1, so 
key=2's aux rows
+    // must be dropped (the inner join with minSeq strips them).
+    val aux = auxTableOf(userSchema)(
+      Row(1, "v1", 5L, null, Row(5L), null),
+      Row(2, "v2", 7L, null, Row(7L), null)
+    )
+    val minSeq = minSeqOf(keySchema)(Row(1, 10L))
+
+    val result = processor.findAffectedRowsFromAuxiliaryTable(
+      rawAuxiliaryTableDf = aux,
+      perKeyMinimumSequenceInMicrobatchDf = minSeq,
+      batchId = 100L
+    )
+
+    checkAnswer(
+      df = result,
+      expectedAnswer = Seq(Row(1, "v1", 5L, null, Row(5L)))
+    )
+  }
+
+  // =============== findAffectedRowsFromTargetTable tests ===============

Review Comment:
   Let's move discussion to this 
[thread](https://github.com/apache/spark/pull/56283#discussion_r3359184147), if 
we decide this case is still meaningful to test I will add. 



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