alamb commented on code in PR #10501:
URL: https://github.com/apache/datafusion/pull/10501#discussion_r1599858102
##########
datafusion/optimizer/src/push_down_limit.rs:
##########
@@ -56,47 +57,12 @@ impl OptimizerRule for PushDownLimit {
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)
- // Before merging:
- // |........skip........|---fetch-->|
Parent Limit
- // |...child_skip...|---child_fetch-->|
Child Limit
- // After merging:
- // |.........(child_skip + skip).........|
- // Before merging:
- // |...skip...|------------fetch------------>|
Parent Limit
- // |...child_skip...|-------------child_fetch------------>|
Child Limit
- // After merging:
- // |....(child_skip + skip)....|---(child_fetch - skip)-->|
-
- // Case 1: Parent is beyond the range of Child. (skip <
child_fetch <= skip + fetch)
- // Before merging:
- // |...skip...|------------fetch------------>|
Parent Limit
- // |...child_skip...|-------------child_fetch------------>|
Child Limit
- // After merging:
- // |....(child_skip + skip)....|---(child_fetch - skip)-->|
-
- // Case 2: Parent is in the range of Child. (skip + fetch <
child_fetch)
- // Before merging:
- // |...skip...|---fetch-->|
Parent Limit
- // |...child_skip...|-------------child_fetch------------>|
Child Limit
- // After merging:
- // |....(child_skip + skip)....|---fetch-->|
- let parent_skip = limit.skip;
- let new_fetch = match (limit.fetch, child.fetch) {
- (Some(fetch), Some(child_fetch)) => {
- Some(min(fetch, child_fetch.saturating_sub(parent_skip)))
- }
- (Some(fetch), None) => Some(fetch),
- (None, Some(child_fetch)) => {
- Some(child_fetch.saturating_sub(parent_skip))
- }
- (None, None) => None,
- };
+ let (skip, fetch) =
+ combine_limit(limit.skip, limit.fetch, child.skip,
child.fetch);
Review Comment:
this PR just refactors all the existing logic to a function
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