doc: Add documentation for pushing limit into plan #20271
+45
−0
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
github-actions
bot
added
optimizer
jonathanc-n
approved these changes
Feb 10, 2026
| //! [`LimitPushdown`] pushes `LIMIT` down through `ExecutionPlan`s to reduce | ||
| //! data transfer as much as possible. | ||
| //! | ||
| //! # Plan Limit Absorption |
Contributor
There was a problem hiding this comment.
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.
Contributor
Author
There was a problem hiding this comment.
Good point, updated!
| //! --- DataSourceExec() | ||
| //! --- DataSourceExec() | ||
| //! ``` | ||
| //! Under this model, `NestedLoopJoinExec` would keep working until it can emit |
Contributor
There was a problem hiding this comment.
Don't we want to give an example with an embedded limit?
Contributor
Author
There was a problem hiding this comment.
Updated, thanks.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
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?