kgyrtkirk commented on a change in pull request #860: HIVE-22408 The fix for
CALCITE-2991 creates wrong results on edge case
URL: https://github.com/apache/hive/pull/860#discussion_r356660051
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File path:
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveSortLimitRemoveRule.java
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@@ -41,8 +42,17 @@ public boolean matches(RelOptRuleCall call) {
final HiveSortLimit sortLimit = call.rel(0);
Double maxRowCount =
call.getMetadataQuery().getMaxRowCount(sortLimit.getInput());
- if (maxRowCount != null &&(maxRowCount <= 1)) {
- return true;
+ if (maxRowCount != null) {
+ if (sortLimit.getFetchExpr() != null) {
+ // we have LIMIT
+ int limit = RexLiteral.intValue(sortLimit.getFetchExpr());
+ if (maxRowCount <= limit) {
Review comment:
if I understand this correctly: this condition seems to be heavily building
on that `MaxRowCount` is an overestimation of the actual rowcount - at any time
that's not the case and it's an underestimation - we may end up removing the
limit.
Because of the above: I think it would make sense to add a toggle to
consider the removal in these cases or not...
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