doc: Add documentation for pushing limit into plan#20271
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xudong963 merged 2 commits intoapache:mainfrom Mar 11, 2026
Merged
doc: Add documentation for pushing limit into plan#20271xudong963 merged 2 commits intoapache:mainfrom
xudong963 merged 2 commits intoapache:mainfrom
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| //! [`LimitPushdown`] pushes `LIMIT` down through `ExecutionPlan`s to reduce | ||
| //! data transfer as much as possible. | ||
| //! | ||
| //! # Plan Limit Absorption |
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Maybe we can mention that with the use of LimitedBatchCoalescer this can allow for passing the limit down and allowing output immediately when the limit is reached.
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Good point, updated!
| //! --- DataSourceExec() | ||
| //! --- DataSourceExec() | ||
| //! ``` | ||
| //! Under this model, `NestedLoopJoinExec` would keep working until it can emit |
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Don't we want to give an example with an embedded limit?
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Updated, thanks.
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## Which issue does this PR close? <!-- We generally require a GitHub issue to be filed for all bug fixes and enhancements and this helps us generate change logs for our releases. You can link an issue to this PR using the GitHub syntax. For example `Closes apache#123` indicates that this PR will close issue apache#123. --> - Closes #. ## Rationale for this change <!-- Why are you proposing this change? If this is already explained clearly in the issue then this section is not needed. Explaining clearly why changes are proposed helps reviewers understand your changes and offer better suggestions for fixes. --> Besides pushing `LimitExec` down the query plan, there is another optimization that allows plan nodes to *absorb* a limit, so it can potentially stop early. I’ve noticed that this form of limit absorption has not been implemented by many operators. This suggests the optimization is non-obvious, so I’d like to improve the documentation for it. A recent PR that implements this optimization is: - apache#20228 ## What changes are included in this PR? <!-- There is no need to duplicate the description in the issue here but it is sometimes worth providing a summary of the individual changes in this PR. --> ## Are these changes tested? <!-- We typically require tests for all PRs in order to: 1. Prevent the code from being accidentally broken by subsequent changes 2. Serve as another way to document the expected behavior of the code If tests are not included in your PR, please explain why (for example, are they covered by existing tests)? --> ## Are there any user-facing changes? <!-- If there are user-facing changes then we may require documentation to be updated before approving the PR. --> <!-- If there are any breaking changes to public APIs, please add the `api change` label. -->
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Which issue does this PR close?
Rationale for this change
Besides pushing
LimitExecdown the query plan, there is another optimization that allows plan nodes to absorb a limit, so it can potentially stop early.I’ve noticed that this form of limit absorption has not been implemented by many operators. This suggests the optimization is non-obvious, so I’d like to improve the documentation for it.
A recent PR that implements this optimization is:
What changes are included in this PR?
Are these changes tested?
Are there any user-facing changes?