gortiz commented on code in PR #8979:
URL: https://github.com/apache/pinot/pull/8979#discussion_r960574343
##########
pinot-core/src/main/java/org/apache/pinot/core/plan/SelectionPlanNode.java:
##########
@@ -50,67 +52,113 @@ public Operator<IntermediateResultsBlock> run() {
List<ExpressionContext> expressions =
SelectionOperatorUtils.extractExpressions(_queryContext, _indexSegment);
int limit = _queryContext.getLimit();
- if (limit > 0) {
- List<OrderByExpressionContext> orderByExpressions =
_queryContext.getOrderByExpressions();
- if (orderByExpressions == null) {
- // Selection only
- TransformOperator transformOperator = new
TransformPlanNode(_indexSegment, _queryContext, expressions,
- Math.min(limit, DocIdSetPlanNode.MAX_DOC_PER_CALL)).run();
- return new SelectionOnlyOperator(_indexSegment, _queryContext,
expressions, transformOperator);
- } else {
- // Selection order-by
- if (isAllOrderByColumnsSorted(orderByExpressions)) {
- // All order-by columns are sorted, no need to sort the records
- TransformOperator transformOperator = new
TransformPlanNode(_indexSegment, _queryContext, expressions,
- Math.min(limit + _queryContext.getOffset(),
DocIdSetPlanNode.MAX_DOC_PER_CALL)).run();
- return new SelectionOrderByOperator(_indexSegment, _queryContext,
expressions, transformOperator, true);
- } else if (orderByExpressions.size() == expressions.size()) {
- // All output expressions are ordered
- TransformOperator transformOperator =
- new TransformPlanNode(_indexSegment, _queryContext, expressions,
DocIdSetPlanNode.MAX_DOC_PER_CALL).run();
- return new SelectionOrderByOperator(_indexSegment, _queryContext,
expressions, transformOperator, false);
- } else {
- // Not all output expressions are ordered, only fetch the order-by
expressions and docId to avoid the
- // unnecessary data fetch
- List<ExpressionContext> expressionsToTransform = new
ArrayList<>(orderByExpressions.size());
- for (OrderByExpressionContext orderByExpression :
orderByExpressions) {
- expressionsToTransform.add(orderByExpression.getExpression());
- }
- TransformOperator transformOperator =
- new TransformPlanNode(_indexSegment, _queryContext,
expressionsToTransform,
- DocIdSetPlanNode.MAX_DOC_PER_CALL).run();
- return new SelectionOrderByOperator(_indexSegment, _queryContext,
expressions, transformOperator, false);
- }
- }
- } else {
+ if (limit == 0) {
// Empty selection (LIMIT 0)
TransformOperator transformOperator = new
TransformPlanNode(_indexSegment, _queryContext, expressions, 0).run();
return new EmptySelectionOperator(_indexSegment, expressions,
transformOperator);
}
+ List<OrderByExpressionContext> orderByExpressions =
_queryContext.getOrderByExpressions();
+
+ if (orderByExpressions == null) {
+ // Selection only
+ // ie: SELECT ... FROM Table WHERE ... LIMIT 10
+ int actualLimit = Math.min(limit, DocIdSetPlanNode.MAX_DOC_PER_CALL);
+ TransformPlanNode planNode = new TransformPlanNode(_indexSegment,
_queryContext, expressions, actualLimit);
+ TransformOperator transformOperator = planNode.run();
+
+ return new SelectionOnlyOperator(_indexSegment, _queryContext,
expressions, transformOperator);
+ }
+ int numOrderByExpressions = orderByExpressions.size();
+ // Although it is a break of abstraction, some code, specially merging,
assumes that if there is an order by
+ // expression the operator will return a block whose selection result is a
priority queue.
+ int sortedColumnsPrefixSize = getSortedColumnsPrefix(orderByExpressions);
Review Comment:
Let me verify if I correctly understand it. Given a table `T` with three
rows where with a single column called `col` whose values are `1`, `null` and
`2`.
1. `col` is considered sorted.
2. If the default null value of `col` is null, `select col from T order by
T` should return `1`, `2`, `null`
Is that right? And if it is... why do we considered `col` a sorted column
if, in fact, it is not sorted in the segment? More formally, given for each d1
and d2 such as d1 < d2 then it is not guaranteed that segment[d1][col] <=
segment[d2][col]
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