kasakrisz commented on a change in pull request #2932:
URL: https://github.com/apache/hive/pull/2932#discussion_r782032263
##########
File path:
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveAggregateSortLimitRule.java
##########
@@ -55,29 +54,13 @@
*/
public class HiveAggregateSortLimitRule extends RelOptRule {
- private static HiveAggregateSortLimitRule instance = null;
-
- public static final HiveAggregateSortLimitRule getInstance(HiveConf
hiveConf) {
- if (instance == null) {
- RelFieldCollation.NullDirection defaultAscNullDirection;
- if (HiveConf.getBoolVar(hiveConf,
HiveConf.ConfVars.HIVE_DEFAULT_NULLS_LAST)) {
- defaultAscNullDirection = RelFieldCollation.NullDirection.LAST;
- } else {
- defaultAscNullDirection = RelFieldCollation.NullDirection.FIRST;
- }
- instance = new HiveAggregateSortLimitRule(defaultAscNullDirection);
- }
-
- return instance;
- }
-
private final RelFieldCollation.NullDirection defaultAscNullDirection;
-
- private HiveAggregateSortLimitRule(RelFieldCollation.NullDirection
defaultAscNullDirection) {
+ public HiveAggregateSortLimitRule(boolean nullsLast) {
Review comment:
I generally avoid hardcoding because the null ordering behavior affects
Top n key operator pushdown optimization.
https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/optimizer/topnkey/TopNKeyPushdownProcessor.java
The `Top N Key` operator introduced into the physical plan as a parent
operator of the `Reduce Sink`. It takes the sort keys and ordering parameters
from the `Reduce Sink`. The push down optimization tries to move TNK until TS
if possible.
More complex queries may have more `Reduce Sinks` or even other TNKs which
should be merged. This is the point where null ordering also count.
I think it is safer to use the config.
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