AnishMahto commented on code in PR #55970: URL: https://github.com/apache/spark/pull/55970#discussion_r3270220391
########## sql/pipelines/src/main/scala/org/apache/spark/sql/pipelines/autocdc/Scd1BatchProcessor.scala: ########## @@ -0,0 +1,161 @@ +/* + * 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.SparkException +import org.apache.spark.sql.{functions => F, AnalysisException} +import org.apache.spark.sql.Column +import org.apache.spark.sql.catalyst.util.QuotingUtils +import org.apache.spark.sql.classic.DataFrame +import org.apache.spark.sql.types.{DataType, StructField, StructType} +import org.apache.spark.util.ArrayImplicits._ + +/** + * Per-microbatch processor for SCD Type 1 AutoCDC flows, complying to the specified [[changeArgs]] + * configuration. + * + * @param changeArgs The CDC flow configuration. + * @param resolvedSequencingType The post-analysis [[DataType]] of the sequencing column, derived + * from the flow's resolved DataFrame at flow setup time. + */ +case class Scd1BatchProcessor( + changeArgs: ChangeArgs, + resolvedSequencingType: DataType) { + + /** + * Deduplicate the incoming CDC microbatch by key, keeping the most recent event per key + * as ordered by [[ChangeArgs.sequencing]]. + * + * For SCD1 we only care about the most recent (by sequence value) event per key. When + * multiple events share the same key and the same sequence value, the row selected is + * non-deterministic and undefined. + * + * The schema of the returned dataframe matches the schema of the microbatch exactly. + */ + def deduplicateMicrobatch(microbatchDf: DataFrame): DataFrame = { + // The `max_by` API can only return a single column, so pack/unpack the entire row into a + // temporary column before and after the `max_by` operation. + val winningRowCol = OutOfOrderCdcMergeUtils.tempColName("__winning_row") + + val allMicrobatchColumns = + microbatchDf.columns + .map(colName => F.col(QuotingUtils.quoteIdentifier(colName))) + .toImmutableArraySeq + + microbatchDf + .groupBy(changeArgs.keys.map(k => F.col(k.quoted)): _*) + .agg( + F.max_by(F.struct(allMicrobatchColumns: _*), changeArgs.sequencing) + .as(winningRowCol) + ) + .select(F.col(s"$winningRowCol.*")) + } + + /** + * Project the CDC metadata column onto the microbatch. + * + * The returned dataframe has all of the columns in the input microbatch + the CDC metadata + * column. + */ + def extendMicrobatchRowsWithCdcMetadata(microbatchDf: DataFrame): DataFrame = { + // Proactively validate the reserved CDC metadata column does not exist in the microbatch. + validateCdcMetadataColumnNotPresent(microbatchDf) + + val rowDeleteSequence: Column = changeArgs.deleteCondition match { + case Some(deleteCondition) => + F.when(deleteCondition, changeArgs.sequencing).otherwise(F.lit(null)) + case None => + F.lit(null) + } + + val rowUpsertSequence: Column = + // A row that is not a delete must be an upsert, these are mutually exclusive and a complete + // set of CDC event types. + F.when(rowDeleteSequence.isNull, changeArgs.sequencing).otherwise(F.lit(null)) + + microbatchDf.withColumn( + Scd1BatchProcessor.cdcMetadataColName, + Scd1BatchProcessor.constructCdcMetadataCol( + deleteSequence = rowDeleteSequence, + upsertSequence = rowUpsertSequence, + sequencingType = resolvedSequencingType + ) + ) + } + + private def validateCdcMetadataColumnNotPresent(microbatchDf: DataFrame): Unit = { + val sqlConf = microbatchDf.sparkSession.sessionState.conf + val resolver = sqlConf.resolver + + microbatchDf.schema.fieldNames + .find(resolver(_, Scd1BatchProcessor.cdcMetadataColName)) + .foreach { conflictingColumnName => + throw new AnalysisException( + errorClass = "AUTOCDC_RESERVED_COLUMN_NAME_CONFLICT", + messageParameters = Map( + "caseSensitivity" -> CaseSensitivityLabels.of(!sqlConf.caseSensitiveAnalysis), + "columnName" -> conflictingColumnName, + "schemaName" -> "microbatch", + "reservedColumnName" -> Scd1BatchProcessor.cdcMetadataColName + ) + ) + } + } +} + +object Scd1BatchProcessor { + private[autocdc] val cdcMetadataColName: String = "_cdc_metadata" + + private[autocdc] val cdcDeleteSequenceFieldName: String = "deleteSequence" Review Comment: Oops, PR description had some stale terminology. 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