[GitHub] [hive] akshat0395 commented on a diff in pull request #3997: HIVE-27000: Improve the modularity of the *ColumnStatsMerger classes

["akshat0395 (via GitHub)" <gi...@apache.org>]

akshat0395 commented on code in PR #3997:
URL: https://github.com/apache/hive/pull/3997#discussion_r1091578039


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standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/columnstats/merge/DateColumnStatsMerger.java:
##########
@@ -43,64 +46,57 @@ public void merge(ColumnStatisticsObj aggregateColStats, ColumnStatisticsObj new
     DateColumnStatsDataInspector aggregateData = dateInspectorFromStats(aggregateColStats);
     DateColumnStatsDataInspector newData = dateInspectorFromStats(newColStats);
 
-    setLowValue(aggregateData, newData);
-    setHighValue(aggregateData, newData);
-
-    aggregateData.setNumNulls(aggregateData.getNumNulls() + newData.getNumNulls());
-    if (aggregateData.getNdvEstimator() == null || newData.getNdvEstimator() == null) {
-      aggregateData.setNumDVs(Math.max(aggregateData.getNumDVs(), newData.getNumDVs()));
-    } else {
-      NumDistinctValueEstimator oldEst = aggregateData.getNdvEstimator();
-      NumDistinctValueEstimator newEst = newData.getNdvEstimator();
-      final long ndv;
-      if (oldEst.canMerge(newEst)) {
-        oldEst.mergeEstimators(newEst);
-        ndv = oldEst.estimateNumDistinctValues();
-        aggregateData.setNdvEstimator(oldEst);
-      } else {
-        ndv = Math.max(aggregateData.getNumDVs(), newData.getNumDVs());
-      }
-      LOG.debug("Use bitvector to merge column {}'s ndvs of {} and {} to be {}", aggregateColStats.getColName(),
-          aggregateData.getNumDVs(), newData.getNumDVs(), ndv);
-      aggregateData.setNumDVs(ndv);
+    Date lowValue = mergeLowValue(getLowValue(aggregateData), getLowValue(newData));
+    if (lowValue != null) {
+      aggregateData.setLowValue(lowValue);
+    }
+    Date highValue = mergeHighValue(getHighValue(aggregateData), getHighValue(newData));
+    if (highValue != null) {

Review Comment:
   This code block seems to be duplicate for multiple StatsMerger classes, can we move this to a shared class to avoid duplication.



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