[GitHub] [hive] okumin commented on a diff in pull request #4353: [WIP, Don't review] HIVE-24240: Implement missing features in UDTFStatsRule

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

okumin commented on code in PR #4353:
URL: https://github.com/apache/hive/pull/4353#discussion_r1203955752


##########
ql/src/java/org/apache/hadoop/hive/ql/optimizer/stats/annotation/StatsRulesProcFactory.java:
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@@ -3066,27 +3066,23 @@ public Object process(Node nd, Stack<Node> stack, NodeProcessorCtx procCtx,
       if (parentStats != null) {
         Statistics st = parentStats.clone();
 
-        float udtfFactor=HiveConf.getFloatVar(aspCtx.getConf(), HiveConf.ConfVars.HIVE_STATS_UDTF_FACTOR);
-        long numRows = (long) (parentStats.getNumRows() * udtfFactor);
+        float udtfFactor = HiveConf.getFloatVar(aspCtx.getConf(), HiveConf.ConfVars.HIVE_STATS_UDTF_FACTOR);
+        long numRows = Math.max(StatsUtils.safeMult(parentStats.getNumRows(), udtfFactor), 1);

Review Comment:
   This change happened on [this discussion](https://github.com/apache/hive/pull/1531#discussion_r500420813) with @kgyrtkirk.
   [Hive's stats will degrade when the number of rows or data size becomes zero](https://github.com/apache/hive/blob/rel/release-4.0.0-alpha-2/ql/src/java/org/apache/hadoop/hive/ql/plan/Statistics.java#L111-L119). So, it is better to keep one row so that Hive can apply full optimization. Ideally, we should explicitly distinguish empty stats from missing stats.



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