cloud-fan commented on code in PR #36295:
URL: https://github.com/apache/spark/pull/36295#discussion_r882685206
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sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/V2ScanRelationPushDown.scala:
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@@ -407,8 +407,65 @@ object V2ScanRelationPushDown extends Rule[LogicalPlan]
with PredicateHelper wit
case other => (other, false)
}
- def pushDownLimits(plan: LogicalPlan): LogicalPlan = plan.transform {
+ private def pushDownOffset(
+ plan: LogicalPlan,
+ offset: Int): Boolean = plan match {
+ case sHolder: ScanBuilderHolder =>
+ val isPushed = PushDownUtils.pushOffset(sHolder.builder, offset)
+ if (isPushed) {
+ sHolder.pushedOffset = Some(offset)
+ }
+ isPushed
+ case p: Project =>
+ pushDownOffset(p.child, offset)
+ case _ => false
+ }
+
+ def pushDownLimitAndOffset(plan: LogicalPlan): LogicalPlan = plan.transform {
+ case offset @ LimitAndOffset(limit, offsetValue, child) =>
+ val (newChild, canRemoveLimit) = pushDownLimit(child, limit)
+ if (canRemoveLimit) {
+ // If we can remove limit, it indicates data source only have one
partition.
+ // For `dataset.limit(m).offset(n)`, try to push down `LIMIT (m - n)
OFFSET n`.
+ // For example, `dataset.limit(5).offset(3)`, we can push down `LIMIT
2 OFFSET 3`.
Review Comment:
This comment makes no sense here. We are pushing down operators, not pushing
down a SQL query to JDBC. It's only a problem in JDBC that `LIMIT x OFFSET y`
means doing OFFSET first, then LIMIT
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