thompsonmax opened a new pull request #27378: [SPARK-30366][WebUI] Show cached subplan of InMemoryTableScan and remove redundant subplans URL: https://github.com/apache/spark/pull/27378 <!-- Thanks for sending a pull request! Here are some tips for you: 1. If this is your first time, please read our contributor guidelines: https://spark.apache.org/contributing.html 2. Ensure you have added or run the appropriate tests for your PR: https://spark.apache.org/developer-tools.html 3. If the PR is unfinished, add '[WIP]' in your PR title, e.g., '[WIP][SPARK-XXXX] Your PR title ...'. 4. Be sure to keep the PR description updated to reflect all changes. 5. Please write your PR title to summarize what this PR proposes. 6. If possible, provide a concise example to reproduce the issue for a faster review. --> ### What changes were proposed in this pull request? 1. Adds a InMemoryRelation node and its cachedPlan as a child node of InMemoryTableScan ([SPARK-29431](https://issues.apache.org/jira/browse/SPARK-29431)). 2. De-duplicate identical subplans shared by InMemoryTableScan operators within the same query ([SPARK-30367](https://issues.apache.org/jira/browse/SPARK-30367)). 3. Add computed rows metric to InMemoryRelation operators ([SPARK-30368](https://issues.apache.org/jira/browse/SPARK-30368)). 4. Prune the cached subplan if it was not actually computed ([SPARK-30369](https://issues.apache.org/jira/browse/SPARK-30369)). <!-- Please clarify what changes you are proposing. The purpose of this section is to outline the changes and how this PR fixes the issue. If possible, please consider writing useful notes for better and faster reviews in your PR. See the examples below. 1. If you refactor some codes with changing classes, showing the class hierarchy will help reviewers. 2. If you fix some SQL features, you can provide some references of other DBMSes. 3. If there is design documentation, please add the link. 4. If there is a discussion in the mailing list, please add the link. --> ### Why are the changes needed? Currently, if a user caches a dataframe as part of the query, it introduces an InMemoryTableScan operator into the query plan when the cached data is read again. The InMemoryTableScan operator does not have child operators and thus doesn't show the subplan of the query that is run before caching the dataframe. However, simply showing the subplan as a child of InMemoryTableScan can lead to some confusion for the user. It is possible for the cached dataframe to be read multiple times within the query, which will cause multiple InMemoryTableScan operators to be shown within the plan and thus cause the subplan to be shown multiple times across the query plan even though it is computed only once. Additionally, it is possible for the cached dataframe to be read in another query. This will cause the subplan to be shown in a query it was not actually computed in, which is misleading, so we should remove it in this case. However, It is also possible for the dataframe to be partially cached, meaning some partitions are cached whereas some need to be recomputed. In this case, we should still show the subplan in the query as it is will still be computed for some partitions of the dataframe. A "num computed rows" metric is added to InMemoryRelation (the child node of InMemoryTableScan which has the subplan as its child) to make it more clear when only some partitions of the cached data are recomputed. <!-- Please clarify why the changes are needed. For instance, 1. If you propose a new API, clarify the use case for a new API. 2. If you fix a bug, you can clarify why it is a bug. --> ### Does this PR introduce any user-facing change? Yes, in the SQL tab of the WebUI. See the JIRA for examples of the WebUI with and without the changes. <!-- If yes, please clarify the previous behavior and the change this PR proposes - provide the console output, description and/or an example to show the behavior difference if possible. If no, write 'No'. --> ### How was this patch tested? * Added unit tests in SparkPlanInfoSuite, CachedRDDBuilderSuite, SparkPlanGraphSuite, SparkPlanGraphUpdaterSuite, and SparkPlanGraphNodeTransformersSuite. * Integration tests using the spark shell to show the desired behavior change in the UI is achieved. <!-- If tests were added, say they were added here. Please make sure to add some test cases that check the changes thoroughly including negative and positive cases if possible. If it was tested in a way different from regular unit tests, please clarify how you tested step by step, ideally copy and paste-able, so that other reviewers can test and check, and descendants can verify in the future. If tests were not added, please describe why they were not added and/or why it was difficult to add. -->
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