AnishMahto commented on code in PR #56208: URL: https://github.com/apache/spark/pull/56208#discussion_r3326817747
########## sql/pipelines/src/main/scala/org/apache/spark/sql/pipelines/autocdc/Scd2BatchProcessor.scala: ########## @@ -0,0 +1,271 @@ +/* + * 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} +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, StructType} + +/** + * Per-microbatch processor for SCD Type 2 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 Scd2BatchProcessor( + changeArgs: ChangeArgs, + resolvedSequencingType: DataType) { + + /** + * Reconcile a CDC microbatch into the canonical form the auxiliary- and target-table merges + * consume. + * + * Step ordering is load-bearing: the row-extension steps reference user data columns that + * target-column selection is allowed to drop, so selection runs last. Unlike SCD1, no per-key + * deduplication step is needed - SCD2 preserves every event as part of the row's history. + * + * Requires the microbatch to have been validated upstream so that the sequencing column is + * non-null and orderable. + */ + private[autocdc] def preprocessMicrobatch(validatedBatchDf: DataFrame): DataFrame = { + validatedBatchDf + .transform(extendMicrobatchRowsWithStartAt) + .transform(extendMicrobatchRowsWithEndAt) + .transform(extendMicrobatchRowsWithCdcMetadata) + .transform(projectTargetColumnsOntoMicrobatch) + } + + /** + * Stamp each microbatch row with its currently known start-at (i.e active-from) using its + * sequencing. + */ + private def extendMicrobatchRowsWithStartAt(microbatchDf: DataFrame): DataFrame = { + microbatchDf.withColumn( + colName = Scd2BatchProcessor.startAtColName, + col = changeArgs.sequencing + ) + } + + /** + * Stamp each microbatch delete event row with its end time sequence, as they are instantaneous + * events. + * + * Non-deletes leave a null end, as do not yet know if the row reprsents an active upsert, or a + * closed upsert. This will become clear in later reconciliation against the aux/target tables. + */ + private def extendMicrobatchRowsWithEndAt(microbatchDf: DataFrame): DataFrame = { + microbatchDf.withColumn( + colName = Scd2BatchProcessor.endAtColName, + col = ( + changeArgs.deleteCondition match { + case Some(deleteCondition) => + F.when(deleteCondition, changeArgs.sequencing).otherwise(null) + case None => + F.lit(null) + } + ).cast(resolvedSequencingType) + ) + } + + /** + * Project the operational CDC metadata column carrying the literal event sequence. Downstream + * merges rely on it to preserve original event lineage regardless of how rows start/end-at are + * coalesced. + */ + private def extendMicrobatchRowsWithCdcMetadata(microbatchDf: DataFrame): DataFrame = { + microbatchDf.withColumn( + colName = AutoCdcReservedNames.cdcMetadataColName, + col = Scd2BatchProcessor.constructCdcMetadataStruct( + recordStartAt = changeArgs.sequencing, + sequencingType = resolvedSequencingType + ) + ) + } + + /** + * Apply the user's target column selection while preserving the SCD2 framework columns; the + * latter are required by downstream merges and persisted to both the auxiliary and target + * tables, so users cannot deselect them. + * + * Requires the framework columns to already be present on the input. + */ + private def projectTargetColumnsOntoMicrobatch( + microbatch: DataFrame + ): DataFrame = { + val dataSchema = StructType( + microbatch.schema.fields.filterNot(f => + Scd2BatchProcessor.reservedFrameworkColNames.contains(f.name) + ) + ) + val userSelectedDataSchema = + ColumnSelection.applyToSchema( + schemaName = "microbatch", + schema = dataSchema, + columnSelection = changeArgs.columnSelection, + caseSensitive = + microbatch.sparkSession.sessionState.conf.caseSensitiveAnalysis + ) + val finalColumnsToSelect: Seq[Column] = + userSelectedDataSchema.fieldNames.toSeq.map(colName => { + // Spark drops backticks in the schema, quote all identifiers for safety before executing + // select. Identifiers could have special characters such as '.'. + F.col(QuotingUtils.quoteIdentifier(colName)) + }) ++ Seq( + F.col(Scd2BatchProcessor.startAtColName), + F.col(Scd2BatchProcessor.endAtColName), + F.col(AutoCdcReservedNames.cdcMetadataColName) + ) + microbatch.select(finalColumnsToSelect: _*) + } + +} + +/** + * Concept: run of upsert events. + * + * A run is a maximal sequence of consecutive upsert events (in sorted order by sequencing) Review Comment: Just a heads up; I explain a bunch of concepts in this scaladoc so readers have context on the `startAt`, `endAt`, and `recordStartAt` columns I introduce below, but none of these concepts are actually actively used in this PR. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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