RussellSpitzer commented on code in PR #6344: URL: https://github.com/apache/iceberg/pull/6344#discussion_r1053776034
########## spark/v3.3/spark/src/main/java/org/apache/iceberg/spark/ChangelogIterator.java: ########## @@ -0,0 +1,203 @@ +/* + * 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.iceberg.spark; + +import java.io.Serializable; +import java.util.Iterator; +import java.util.List; +import java.util.Objects; +import org.apache.iceberg.ChangelogOperation; +import org.apache.iceberg.relocated.com.google.common.collect.Iterators; +import org.apache.spark.sql.Row; +import org.apache.spark.sql.RowFactory; +import org.apache.spark.sql.catalyst.expressions.GenericInternalRow; +import org.apache.spark.sql.catalyst.expressions.GenericRowWithSchema; + +/** + * An iterator that transforms rows from changelog tables within a single Spark task. It assumes + * that rows are sorted by identifier columns and change type. + * + * <p>It removes the carry-over rows. Carry-over rows are unchanged rows in a snapshot but showed as Review Comment: I was working a little on re-wording this a bit? Feel free to use any of this if you like Carry-over rows are the result of a removal and addition of the same row within an operation because of the copy-on-write mechanism. The iterator uses the "identifier fields" to determine of two rows are identical. For example, given a file which contains row1 (id=1, data='a') and row2 (id=2, data='b'). in a data file, a copy-on-write delete of row2 would require erasing this file. To preserve row1 a new file is written with row1' which is identical to row1. The change-log table would report this as (row1 deleted, row1' added), since this row was not actually modified it is not an actual change in the table. One function of this iterator is to remove these carry-over rows. -- 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. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
