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The following commit(s) were added to refs/heads/main by this push:
new f22007717a fix: clear handled OFFSET before child recursion in
LimitPushdown (#22525)
f22007717a is described below
commit f22007717a9f874020b6e1d0c994ec22325a0257
Author: Kumar Ujjawal <[email protected]>
AuthorDate: Wed May 27 21:47:58 2026 +0530
fix: clear handled OFFSET before child recursion in LimitPushdown (#22525)
## 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 #22489.
## Rationale for this change
`LimitPushdown` carries `GlobalRequirements` while walking the physical
plan.
In the bad plan shape from #22489, an outer `OFFSET` was already handled
above
a sort barrier, but its `skip` still remained in the state when
recursion
continued into the child subtree. That stale `skip` then merged with an
inner
`LIMIT` and reduced its fetch incorrectly, which caused a grouped row to
be
dropped.
The fix is to clear `skip` once the limit requirement has already been
handled,
while keeping `fetch` so valid limit pushdown into child sorts still
happens.
<!--
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.
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## What changes are included in this PR?
- Clear `skip` before recursing into children when the limit requirement
is already handled.
- Keep `fetch` unchanged so valid TopK-style pushdown still works.
- Add a physical optimizer regression test for the exact outer `OFFSET`
/ sort barrier / inner `LIMIT` shape.
- Add an end-to-end sqllogictest for the SQL reproducer from #22489.
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is sometimes worth providing a summary of the individual changes in this
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## Are these changes tested?
Yes
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## Are there any user-facing changes?
No API Change
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---
.../tests/physical_optimizer/limit_pushdown.rs | 120 +++++++++++++++++++++
.../physical-optimizer/src/limit_pushdown.rs | 8 ++
datafusion/sqllogictest/test_files/limit.slt | 55 ++++++++++
3 files changed, 183 insertions(+)
diff --git a/datafusion/core/tests/physical_optimizer/limit_pushdown.rs
b/datafusion/core/tests/physical_optimizer/limit_pushdown.rs
index 572ae83540..b8ebc80348 100644
--- a/datafusion/core/tests/physical_optimizer/limit_pushdown.rs
+++ b/datafusion/core/tests/physical_optimizer/limit_pushdown.rs
@@ -714,3 +714,123 @@ fn no_limit_preserves_plan_identity() -> Result<()> {
Ok(())
}
+
+#[test]
+fn outer_offset_does_not_leak_through_sort_into_inner_limit() -> Result<()> {
+ // Regression test for https://github.com/apache/datafusion/issues/22489
+ //
+ // When an outer OFFSET is separated from an inner LIMIT by a SortExec
+ // with different sort keys, the outer skip must not reduce the inner
+ // fetch. Before the fix, combine_limit merged them, producing
+ // GlobalLimitExec(skip=1, fetch=7) instead of preserving the inner
+ // LIMIT 8.
+ //
+ // Plan structure:
+ // GlobalLimitExec: skip=1, fetch=None (outer OFFSET 1)
+ // SortExec: [c1 DESC] (outer sort — different key)
+ // GlobalLimitExec: skip=0, fetch=8 (inner LIMIT 8)
+ // SortExec: [c2 ASC] (inner sort — different key)
+ // EmptyExec
+ let schema = create_schema();
+ let empty = empty_exec(Arc::clone(&schema));
+
+ let inner_ordering: LexOrdering = [PhysicalSortExpr {
+ expr: col("c2", &schema)?,
+ options: SortOptions::default(),
+ }]
+ .into();
+ let inner_sort = sort_exec(inner_ordering, empty);
+ let inner_limit = global_limit_exec(inner_sort, 0, Some(8));
+
+ let outer_ordering: LexOrdering = [PhysicalSortExpr {
+ expr: col("c1", &schema)?,
+ options: SortOptions {
+ descending: true,
+ nulls_first: false,
+ },
+ }]
+ .into();
+ let outer_sort = sort_exec(outer_ordering, inner_limit);
+ let outer_limit = global_limit_exec(outer_sort, 1, None);
+
+ let initial = format_plan(&outer_limit);
+ insta::assert_snapshot!(
+ initial,
+ @r"
+ GlobalLimitExec: skip=1, fetch=None
+ SortExec: expr=[c1@0 DESC NULLS LAST], preserve_partitioning=[false]
+ GlobalLimitExec: skip=0, fetch=8
+ SortExec: expr=[c2@1 ASC], preserve_partitioning=[false]
+ EmptyExec
+ "
+ );
+
+ let after_optimize =
+ LimitPushdown::new().optimize(outer_limit, &ConfigOptions::new())?;
+ let optimized = format_plan(&after_optimize);
+ insta::assert_snapshot!(
+ optimized,
+ @r"
+ GlobalLimitExec: skip=1, fetch=None
+ SortExec: expr=[c1@0 DESC NULLS LAST], preserve_partitioning=[false]
+ SortExec: TopK(fetch=8), expr=[c2@1 ASC], preserve_partitioning=[false]
+ EmptyExec
+ "
+ );
+
+ Ok(())
+}
+
+#[test]
+fn outer_offset_with_same_sort_key_still_pushes_limit() -> Result<()> {
+ // Companion to outer_offset_does_not_leak_through_sort_into_inner_limit:
+ // when both sorts use the *same* key, the inner LIMIT should still be
+ // pushed into the SortExec as TopK.
+ //
+ // Plan structure:
+ // GlobalLimitExec: skip=1, fetch=None (outer OFFSET 1)
+ // SortExec: [c1 ASC] (outer sort — same key)
+ // GlobalLimitExec: skip=0, fetch=8 (inner LIMIT 8)
+ // SortExec: [c1 ASC] (inner sort — same key)
+ // EmptyExec
+ let schema = create_schema();
+ let empty = empty_exec(Arc::clone(&schema));
+
+ let ordering: LexOrdering = [PhysicalSortExpr {
+ expr: col("c1", &schema)?,
+ options: SortOptions::default(),
+ }]
+ .into();
+
+ let inner_sort = sort_exec(ordering.clone(), empty);
+ let inner_limit = global_limit_exec(inner_sort, 0, Some(8));
+ let outer_sort = sort_exec(ordering, inner_limit);
+ let outer_limit = global_limit_exec(outer_sort, 1, None);
+
+ let initial = format_plan(&outer_limit);
+ insta::assert_snapshot!(
+ initial,
+ @r"
+ GlobalLimitExec: skip=1, fetch=None
+ SortExec: expr=[c1@0 ASC], preserve_partitioning=[false]
+ GlobalLimitExec: skip=0, fetch=8
+ SortExec: expr=[c1@0 ASC], preserve_partitioning=[false]
+ EmptyExec
+ "
+ );
+
+ let after_optimize =
+ LimitPushdown::new().optimize(outer_limit, &ConfigOptions::new())?;
+ let optimized = format_plan(&after_optimize);
+ insta::assert_snapshot!(
+ optimized,
+ @r"
+ GlobalLimitExec: skip=1, fetch=None
+ SortExec: expr=[c1@0 ASC], preserve_partitioning=[false]
+ SortExec: TopK(fetch=8), expr=[c1@0 ASC], preserve_partitioning=[false]
+ EmptyExec
+ "
+ );
+
+ Ok(())
+}
diff --git a/datafusion/physical-optimizer/src/limit_pushdown.rs
b/datafusion/physical-optimizer/src/limit_pushdown.rs
index 6164d86e53..63c4f21bd9 100644
--- a/datafusion/physical-optimizer/src/limit_pushdown.rs
+++ b/datafusion/physical-optimizer/src/limit_pushdown.rs
@@ -375,6 +375,14 @@ pub(crate) fn pushdown_limits(
(new_node, global_state) = pushdown_limit_helper(new_node.data,
global_state)?;
}
+ // Once a limit has been materialized above the current node, child
+ // subtrees should not inherit its `skip`. Keep `fetch`, but clear
+ // `skip` before recursing so child-local limits are not merged with
+ // an `OFFSET` that has already been applied.
+ if global_state.satisfied {
+ global_state.skip = 0;
+ }
+
// Apply pushdown limits in children
let children = new_node.data.children();
let mut changed = false;
diff --git a/datafusion/sqllogictest/test_files/limit.slt
b/datafusion/sqllogictest/test_files/limit.slt
index fc62584dc3..ca2b36727d 100644
--- a/datafusion/sqllogictest/test_files/limit.slt
+++ b/datafusion/sqllogictest/test_files/limit.slt
@@ -989,3 +989,58 @@ c-4
statement ok
DROP TABLE t21176;
+
+# Regression test for https://github.com/apache/datafusion/issues/22489
+# An outer ORDER BY / OFFSET must not reduce an inner LIMIT when the two are
+# separated by a sort on a *different* key.
+
+statement ok
+set datafusion.execution.target_partitions = 4;
+
+statement ok
+CREATE TABLE t22489 (g INT, x INT, y INT) AS VALUES (1, 10, 4), (2, 20, 3),
(3, 30, 2), (4, 40, 1);
+
+# Inner ORDER BY sx DESC LIMIT 4 keeps all four groups; the outer ORDER BY
+# sy DESC OFFSET 1 then drops only the sy-max group (g=1), so g=2,3,4 remain.
+query III
+SELECT * FROM (
+ SELECT g, SUM(x) AS sx, SUM(y) AS sy FROM t22489 GROUP BY g
+ ORDER BY sx DESC LIMIT 4
+) q
+ORDER BY sy DESC
+OFFSET 1;
+----
+2 20 3
+3 30 2
+4 40 1
+
+query TT
+EXPLAIN
+SELECT * FROM (
+ SELECT g, SUM(x) AS sx, SUM(y) AS sy FROM t22489 GROUP BY g
+ ORDER BY sx DESC LIMIT 4
+) q
+ORDER BY sy DESC
+OFFSET 1;
+----
+logical_plan
+01)Limit: skip=1, fetch=None
+02)--Sort: q.sy DESC NULLS FIRST
+03)----SubqueryAlias: q
+04)------Sort: sx DESC NULLS FIRST, fetch=4
+05)--------Projection: t22489.g, sum(t22489.x) AS sx, sum(t22489.y) AS sy
+06)----------Aggregate: groupBy=[[t22489.g]], aggr=[[sum(CAST(t22489.x AS
Int64)), sum(CAST(t22489.y AS Int64))]]
+07)------------TableScan: t22489 projection=[g, x, y]
+physical_plan
+01)GlobalLimitExec: skip=1, fetch=None
+02)--SortExec: expr=[sy@2 DESC], preserve_partitioning=[false]
+03)----SortPreservingMergeExec: [sx@1 DESC], fetch=4
+04)------SortExec: TopK(fetch=4), expr=[sx@1 DESC],
preserve_partitioning=[true]
+05)--------ProjectionExec: expr=[g@0 as g, sum(t22489.x)@1 as sx,
sum(t22489.y)@2 as sy]
+06)----------AggregateExec: mode=FinalPartitioned, gby=[g@0 as g],
aggr=[sum(t22489.x), sum(t22489.y)]
+07)------------RepartitionExec: partitioning=Hash([g@0], 4), input_partitions=1
+08)--------------AggregateExec: mode=Partial, gby=[g@0 as g],
aggr=[sum(t22489.x), sum(t22489.y)]
+09)----------------DataSourceExec: partitions=1, partition_sizes=[1]
+
+statement ok
+DROP TABLE t22489;
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