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Posted to github@datafusion.apache.org by "masonh22 (via GitHub)" <gi...@apache.org> on 2026/09/21 19:58:49 UTC
[PR] Fix `EliminateLimit` not eliminating limits under `LogicalPlan::Extension` nodes. [datafusion]
masonh22 opened a new pull request, #25577:
URL: https://github.com/apache/datafusion/pull/25577
## Which issue does this PR close?
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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 #123` indicates that this PR will close issue #123.
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- Closes #.
## Rationale for this change
#22298 updated the logical plan optimizer to apply optimization rules in place to avoid `Arc` unwrap/rewraps with a new `map_children_mut()` function. This function unconditionally updates the children of all logical plan nodes except for `LogicalPlan::Extension` nodes. For `Extension` nodes, it only updates the children if the mapping function returns `true` for any of the children, signifying that a child was updated.
When the `EliminateLimit` rule prunes a limit that has 0 skip and fetch, it modifies the node but does not return that it modified anything. This is fine for every case except for if the limit is underneath a `LogicalPlan::Extension` node, since it that case we ignore the output from the rule.
## What changes are included in this PR?
This change adds a failing test, a fix to `EliminateLimit`, and changes `map_children_mut()` to unconditionally update the children of `LogicalPlan::Extension` nodes. The change to `map_children_mut()` could be left out, but I wouldn't be surprised if there are other optimization rules that modify the node without returning `transformed=true`, so this is done to avoid finding and fixing all of those cases.
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## What is the testing strategy for this PR?
I added a test that replicates the issue and fails without my fixes.
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## Are there any user-facing changes?
No
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Re: [PR] Fix `EliminateLimit` not eliminating limits under `LogicalPlan::Extension` nodes. [datafusion]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb merged PR #25577:
URL: https://github.com/apache/datafusion/pull/25577
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Re: [PR] Fix `EliminateLimit` not eliminating limits under `LogicalPlan::Extension` nodes. [datafusion]
Posted by "martin-g (via GitHub)" <gi...@apache.org>.
martin-g commented on code in PR #25577:
URL: https://github.com/apache/datafusion/pull/25577#discussion_r4070737202
##########
datafusion/optimizer/src/eliminate_limit.rs:
##########
@@ -78,7 +78,10 @@ impl OptimizerRule for EliminateLimit {
// If fetch is `None` and skip is 0, then Limit takes no effect and
// we can remove it. Its input also can be Limit, so we should apply again.
#[expect(clippy::used_underscore_binding)]
- return self.rewrite(Arc::unwrap_or_clone(limit.input), _config);
Review Comment:
unrelated: It is a good moment to rename `_config` to `config` because obviously it is being used.
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Re: [PR] Fix `EliminateLimit` not eliminating limits under `LogicalPlan::Extension` nodes. [datafusion]
Posted by "martin-g (via GitHub)" <gi...@apache.org>.
martin-g commented on code in PR #25577:
URL: https://github.com/apache/datafusion/pull/25577#discussion_r4071857582
##########
datafusion/optimizer/src/eliminate_limit.rs:
##########
@@ -78,7 +78,10 @@ impl OptimizerRule for EliminateLimit {
// If fetch is `None` and skip is 0, then Limit takes no effect and
// we can remove it. Its input also can be Limit, so we should apply again.
#[expect(clippy::used_underscore_binding)]
- return self.rewrite(Arc::unwrap_or_clone(limit.input), _config);
Review Comment:
Looks good to me!
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Re: [PR] Fix `EliminateLimit` not eliminating limits under `LogicalPlan::Extension` nodes. [datafusion]
Posted by "masonh22 (via GitHub)" <gi...@apache.org>.
masonh22 commented on code in PR #25577:
URL: https://github.com/apache/datafusion/pull/25577#discussion_r4071760338
##########
datafusion/optimizer/src/eliminate_limit.rs:
##########
@@ -78,7 +78,10 @@ impl OptimizerRule for EliminateLimit {
// If fetch is `None` and skip is 0, then Limit takes no effect and
// we can remove it. Its input also can be Limit, so we should apply again.
#[expect(clippy::used_underscore_binding)]
- return self.rewrite(Arc::unwrap_or_clone(limit.input), _config);
Review Comment:
I actually kind of like it like this. It's only being used for the recursive call, so in a way it is unused.
Although maybe the better way to do this is to make a `rewrite_inner()` function that doesn't have the config argument. I will try that out
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Re: [PR] Fix `EliminateLimit` not eliminating limits under `LogicalPlan::Extension` nodes. [datafusion]
Posted by "masonh22 (via GitHub)" <gi...@apache.org>.
masonh22 commented on code in PR #25577:
URL: https://github.com/apache/datafusion/pull/25577#discussion_r4071804425
##########
datafusion/optimizer/src/eliminate_limit.rs:
##########
@@ -78,7 +78,10 @@ impl OptimizerRule for EliminateLimit {
// If fetch is `None` and skip is 0, then Limit takes no effect and
// we can remove it. Its input also can be Limit, so we should apply again.
#[expect(clippy::used_underscore_binding)]
- return self.rewrite(Arc::unwrap_or_clone(limit.input), _config);
Review Comment:
Updated in [3804933](https://github.com/apache/datafusion/pull/25577/commits/3804933cfe1d25e19dc5dde7fbb8981dbf4e5e6d), let me know what you think (I'm also happy to go with what you initially suggested)
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Re: [PR] Fix `EliminateLimit` not eliminating limits under `LogicalPlan::Extension` nodes. [datafusion]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on code in PR #25577:
URL: https://github.com/apache/datafusion/pull/25577#discussion_r4076433965
##########
datafusion/optimizer/src/eliminate_limit.rs:
##########
@@ -77,8 +83,9 @@ impl OptimizerRule for EliminateLimit {
} else if matches!(limit.get_skip_type()?, SkipType::Literal(0)) {
// If fetch is `None` and skip is 0, then Limit takes no effect and
// we can remove it. Its input also can be Limit, so we should apply again.
- #[expect(clippy::used_underscore_binding)]
- return self.rewrite(Arc::unwrap_or_clone(limit.input), _config);
+ let mut res = Self::rewrite_inner(Arc::unwrap_or_clone(limit.input))?;
Review Comment:
the idea here is to apply the limit pushdown on the inner as well here? Aka keep recursing
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Re: [PR] Fix `EliminateLimit` not eliminating limits under `LogicalPlan::Extension` nodes. [datafusion]
Posted by "masonh22 (via GitHub)" <gi...@apache.org>.
masonh22 commented on code in PR #25577:
URL: https://github.com/apache/datafusion/pull/25577#discussion_r4082916175
##########
datafusion/optimizer/src/eliminate_limit.rs:
##########
@@ -77,8 +83,9 @@ impl OptimizerRule for EliminateLimit {
} else if matches!(limit.get_skip_type()?, SkipType::Literal(0)) {
// If fetch is `None` and skip is 0, then Limit takes no effect and
// we can remove it. Its input also can be Limit, so we should apply again.
- #[expect(clippy::used_underscore_binding)]
- return self.rewrite(Arc::unwrap_or_clone(limit.input), _config);
+ let mut res = Self::rewrite_inner(Arc::unwrap_or_clone(limit.input))?;
Review Comment:
Hmmm, good question. We shouldn't need to recurse here since the mechanism that actually calls the optimizer rules should handle that. Also, the apply order is `BottomUp` for this so it should've been called on the child already. So I think this might be unnecessary. Let me try removing it.
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Re: [PR] Fix `EliminateLimit` not eliminating limits under `LogicalPlan::Extension` nodes. [datafusion]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on code in PR #25577:
URL: https://github.com/apache/datafusion/pull/25577#discussion_r4076433965
##########
datafusion/optimizer/src/eliminate_limit.rs:
##########
@@ -77,8 +83,9 @@ impl OptimizerRule for EliminateLimit {
} else if matches!(limit.get_skip_type()?, SkipType::Literal(0)) {
// If fetch is `None` and skip is 0, then Limit takes no effect and
// we can remove it. Its input also can be Limit, so we should apply again.
- #[expect(clippy::used_underscore_binding)]
- return self.rewrite(Arc::unwrap_or_clone(limit.input), _config);
+ let mut res = Self::rewrite_inner(Arc::unwrap_or_clone(limit.input))?;
Review Comment:
the idea here is to apply the limit pushdown on the inner as well here?
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Re: [PR] Fix `EliminateLimit` not eliminating limits under `LogicalPlan::Extension` nodes. [datafusion]
Posted by "masonh22 (via GitHub)" <gi...@apache.org>.
masonh22 commented on code in PR #25577:
URL: https://github.com/apache/datafusion/pull/25577#discussion_r4083353150
##########
datafusion/optimizer/src/eliminate_limit.rs:
##########
@@ -77,8 +83,9 @@ impl OptimizerRule for EliminateLimit {
} else if matches!(limit.get_skip_type()?, SkipType::Literal(0)) {
// If fetch is `None` and skip is 0, then Limit takes no effect and
// we can remove it. Its input also can be Limit, so we should apply again.
- #[expect(clippy::used_underscore_binding)]
- return self.rewrite(Arc::unwrap_or_clone(limit.input), _config);
+ let mut res = Self::rewrite_inner(Arc::unwrap_or_clone(limit.input))?;
Review Comment:
The tests passed on my machine without the recursive call, so I don't think this was necessary. I removed it in [9fcc605](https://github.com/apache/datafusion/pull/25577/commits/9fcc605de088994411a1b837766e31b36b1f3b8c).
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Re: [PR] Fix `EliminateLimit` not eliminating limits under `LogicalPlan::Extension` nodes. [datafusion]
Posted by "codecov-commenter (via GitHub)" <gi...@apache.org>.
codecov-commenter commented on PR #25577:
URL: https://github.com/apache/datafusion/pull/25577#issuecomment-5766991749
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<details><summary>Additional details and impacted files</summary>
```diff
@@ Coverage Diff @@
## main #25577 +/- ##
=======================================
Coverage 82.42% 82.42%
=======================================
Files 1139 1139
Lines 435372 435386 +14
Branches 435372 435386 +14
=======================================
+ Hits 358845 358860 +15
+ Misses 54826 54818 -8
- Partials 21701 21708 +7
```
</details>
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