fix(planner): disable project block merge in non-top-level subplans

[JinqingKuang]

Description

fix(planner): disable project block merge in non-top-level subplans

Issue(s)

• Fix: https://project.feishu.cn/taosdata_td/defect/detail/6825791030

Checklist

Please check the items in the checklist if applicable.

• Is the user manual updated?
• Are the test cases passed and automated?
• Is there no significant decrease in test coverage?

[gemini-code-assist]

Summary of Changes

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This pull request refines the query planner's behavior by conditionally disabling the merging of project blocks within subplans. The change ensures that project nodes only merge data blocks when they are the root output of a top-level subplan, preventing incorrect optimizations that could lead to issues like query hangs. A new test case has been added to validate this specific behavior.

Highlights

• Planner Logic Update: Modified the projectCanMergeDataBlock function to prevent project block merging in non-top-level subplans or when the project node is not the root output of a top-level subplan. This addresses potential issues with subplan processing.
• Function Signature Change: Updated the projectCanMergeDataBlock and createProjectPhysiNode function signatures to include a topLevelSubplan parameter, which is derived from the subplan's level.
• New Test Case Added: Introduced a new Python test case to specifically verify that the 'Projection Merge ResBlocks' flag is correctly set to False in the explain plan for queries involving subqueries with interval and sliding windows, confirming the fix.

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Changelog

• source/libs/planner/src/planPhysiCreater.c
  • Modified projectCanMergeDataBlock to accept a topLevelSubplan boolean parameter and added logic to prevent merging if it's not a top-level subplan or has a parent.
  • Updated createProjectPhysiNode to pass the subplan's level (indicating top-level status) to projectCanMergeDataBlock.
  • Adjusted the call to createProjectPhysiNode within doCreatePhysiNode to include the pSubplan argument.
• test/cases/13-TimeSeriesExt/03-TimeWindow/test_interval_project_merge_resblock.py
  • Added a new test file test_interval_project_merge_resblock.py to verify the correct behavior of project block merging in subqueries with interval and sliding windows.
  • Implemented a helper function _assert_projection_merge_resblock_false to parse explain plans and assert that 'Projection Merge ResBlocks' is set to False.

Activity

• The test cases have been passed and automated.
• There is no significant decrease in test coverage.

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[Copilot]

Pull request overview

This pull request fixes an issue where project block merging in non-top-level subplans was causing interval query hangs. The fix disables the merge optimization for projection nodes that are not at the root of the top-level subplan.

Changes:

• Modified projectCanMergeDataBlock function to accept a topLevelSubplan parameter and added logic to disallow merging when not at the top level or when the projection has a parent
• Updated createProjectPhysiNode to pass the subplan object and determine if it's top-level based on subplan->level == 0
• Added regression test to verify the fix by checking the explain plan output

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
source/libs/planner/src/planPhysiCreater.c	Added top-level subplan check to projectCanMergeDataBlock function and updated createProjectPhysiNode signature to pass subplan
test/cases/13-TimeSeriesExt/03-TimeWindow/test_interval_project_merge_resblock.py	Added regression test that verifies Projection Merge ResBlocks is set to False in explain plan

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[gemini-code-assist]

Code Review

This pull request disables project block merging for non-top-level subplans to fix a planner issue. The changes in planPhysiCreater.c introduce a topLevelSubplan flag to projectCanMergeDataBlock to control this behavior. The call sites are updated accordingly. A new Python test is added to verify that the Merge ResBlocks flag is correctly set to False in the EXPLAIN plan for a query with a non-terminal projection node. The logic appears sound and the test case effectively validates the fix.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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