[GitHub] [iceberg] openinx commented on a change in pull request #2276: Core: Add option to combine tasks by partition

[GitBox <gi...@apache.org>]

openinx commented on a change in pull request #2276:
URL: https://github.com/apache/iceberg/pull/2276#discussion_r590959223



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File path: api/src/main/java/org/apache/iceberg/TableScan.java
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@@ -181,6 +181,34 @@ default TableScan select(String... columns) {
    */
   CloseableIterable<CombinedScanTask> planTasks();
 
+  /**
+   * Create a new {@link TableScan} which indicate that when plan tasks via the
+   * {@link #planTasks()}, the scan should preserve partition boundary specified by the provided
+   * partition column names. In other words, the scan will not attempt to combine tasks whose input
+   * files have different partition data w.r.t `columns`.
+   *
+   * @param columns the partition column names to preserve boundary when planning tasks
+   * @return a table scan preserving partition boundary when planning tasks
+   * @throws IllegalArgumentException if any of the input columns is not a partition column, or
+   *         if the table is unpartitioned, or `columns` is empty.
+   */
+  TableScan preservePartitions(Collection<String> columns);

Review comment:
       I agreed that it's great to provide a API in `TableScan`  to plan tasks GROUP BY partitions, actually we have lots of duplicated codes in [RewriteDataFilesAction](https://github.com/apache/iceberg/blob/e2a0ba4e34d5f5d3cc80a2a659d50651980fe1b1/core/src/main/java/org/apache/iceberg/actions/BaseRewriteDataFilesAction.java#L212) to rewrite data files per partition.  After introduced this API , I think we could simplify the logic of Rewrite action ( In format v2, we will have more rewrite actions).
   
   One question is:  what's the case that we want to group task by subset of partition columns ? In my mind, we usually group the tasks by the full set of partition columns..




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