imback82 opened a new pull request #26476: [SPARK-29851][SQL] V2 catalog: Change default behavior of dropping namespace to cascade URL: https://github.com/apache/spark/pull/26476 ### What changes were proposed in this pull request? <!-- 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. --> Currently, `SupportsNamespaces.dropNamespace` drops a namespace only if it is empty. Thus, to implement a cascading drop, one needs to iterate all objects (tables, view, etc.) within the namespace (including its sub-namespaces recursively) and drop them one by one. This can have a negative impact on the performance when there are large number of objects. Instead, this PR proposes to change the default behavior of dropping a namespace to cascading such that implementing cascading/non-cascading drop is simpler without performance penalties. ### Why are the changes needed? <!-- 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. --> The new behavior makes implementing cascading/non-cascading drop simple without performance penalties. ### Does this PR introduce any user-facing change? <!-- 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'. --> Yes. The default behavior of `SupportsNamespaces.dropNamespace` is now cascading. ### How was this patch tested? <!-- 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. --> Added new unit tests.
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