ngsg commented on code in PR #5674:
URL: https://github.com/apache/hive/pull/5674#discussion_r2021220624
##########
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/columnstats/aggr/LongColumnStatsAggregator.java:
##########
@@ -242,6 +242,24 @@ public ColumnStatisticsObj
aggregate(List<ColStatsObjWithSourceInfo> colStatsWit
}
statsObj.setStatsData(columnStatisticsData);
+
+ // NDV cannot exceed the number of integers within the given range.
+ long numIntInRange = columnStatisticsData.getLongStats().getHighValue()
Review Comment:
```
densityAvgSum += ((double) (newData.getHighValue() - newData.getLowValue()))
/ newData.getNumDVs();
```
There might be an invariant such as columnStats being present implies `NDV
!= 0`, but it's safer to explicitly guard against division by zero. I'll update
the code accordingly.
---
```
double densityAvg = densityAvgSum / partNames.size();
```
If `partNames.size()` is 0, we should return an empty ColumnStats or null,
as there's nothing to aggregate. I'll check the convention and adjust the code
to handle this case properly.
---
```
estimation = (long) ((aggregateData.getHighValue() -
aggregateData.getLowValue()) / densityAvg);
```
It seems that `densityAvg` is 0 in some cases. I'll fix it as well.
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