alamb commented on code in PR #5021:
URL: https://github.com/apache/arrow-datafusion/pull/5021#discussion_r1086502979
##########
datafusion/optimizer/src/push_down_limit.rs:
##########
@@ -37,104 +37,97 @@ impl PushDownLimit {
}
}
-fn is_no_join_condition(join: &Join) -> bool {
- join.on.is_empty() && join.filter.is_none()
-}
-
-fn push_down_join(
- join: &Join,
- left_limit: Option<usize>,
- right_limit: Option<usize>,
-) -> LogicalPlan {
- let left = match left_limit {
- Some(limit) => LogicalPlan::Limit(Limit {
- skip: 0,
- fetch: Some(limit),
- input: Arc::new((*join.left).clone()),
- }),
- None => (*join.left).clone(),
- };
- let right = match right_limit {
- Some(limit) => LogicalPlan::Limit(Limit {
- skip: 0,
- fetch: Some(limit),
- input: Arc::new((*join.right).clone()),
- }),
- None => (*join.right).clone(),
- };
- LogicalPlan::Join(Join {
- left: Arc::new(left),
- right: Arc::new(right),
- on: join.on.clone(),
- filter: join.filter.clone(),
- join_type: join.join_type,
- join_constraint: join.join_constraint,
- schema: join.schema.clone(),
- null_equals_null: join.null_equals_null,
- })
-}
-
/// Push down Limit.
impl OptimizerRule for PushDownLimit {
fn try_optimize(
&self,
plan: &LogicalPlan,
_config: &dyn OptimizerConfig,
) -> Result<Option<LogicalPlan>> {
+ use std::cmp::min;
+
let limit = match plan {
LogicalPlan::Limit(limit) => limit,
_ => return Ok(None),
};
- if let LogicalPlan::Limit(child_limit) = &*limit.input {
+ if let LogicalPlan::Limit(child) = &*limit.input {
+ // Merge the Parent Limit and the Child Limit.
+
+ // Case 0: Parent and Child are disjoint. (child_fetch <= skip)
Review Comment:
these pictures are wonderfully helpful -- thank you @HaoYang670
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