HIVE-22248 Fix statistics persisting issues #801
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jcamachor
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Oct 3, 2019
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| private double getMinValue(DoubleColumnStatsDataInspector aggregateData, DoubleColumnStatsDataInspector newData) { | ||
| if (!aggregateData.isSetLowValue() && !newData.isSetLowValue()) { | ||
| return 0; |
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If they are both unset, why do we return 0 here instead of leaving it unset? I am not sure whether this will ever happen, but it seems the right behavior.
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My original logic was that the value for the statistics should be 0 (as we don't have anything for that column yet), but I agree with you, it is nicer to leave it unset in this case. In effect it's the same, but the code is cleaner. Fixed.
miklosgergely
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jcamachor
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Oct 3, 2019
| @@ -30,7 +30,7 @@ | |||
| public void merge(ColumnStatisticsObj aggregateColStats, ColumnStatisticsObj newColStats) { | |||
| DoubleColumnStatsDataInspector aggregateData = doubleInspectorFromStats(aggregateColStats); | |||
| DoubleColumnStatsDataInspector newData = doubleInspectorFromStats(newColStats); | |||
| aggregateData.setLowValue(Math.min(aggregateData.getLowValue(), newData.getLowValue())); | |||
| setMinValue(aggregateData, newData); | |||
| aggregateData.setHighValue(Math.max(aggregateData.getHighValue(), newData.getHighValue())); | |||
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Should we do the same for high value?
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During the thrift call the XXXXColumnStatsDataInspector was transformed into a XXXXColumnStatsData object, which then was converted back, by calling the xxxxInspectorFromStats functions. The new object was never put back though to the aggregateStats, so all the modifications made by the XXXXColumnStatsMerger was made on an object that was never used again. Added aggregateColStats.getStatsData().setXXXXStats(aggregateData); calls to put them there, so the changes made by the merger are actually in effect.
The min value was miscalculated for Long and Double types, as the null value was treated as 0. It was fixed by calculating the min values by also using the isSetLowValue() function.
In case of vector_coalesce_3.q the bad statistics made the engine "think" that the column is a primary key following some heuristics based on statistics, and made it guess the statistics in a different way, thus is the output change.