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Posted to gitbox@hive.apache.org by "konstantinb (via GitHub)" <gi...@apache.org> on 2026/02/09 16:04:46 UTC

[PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

konstantinb opened a new pull request, #6308:
URL: https://github.com/apache/hive/pull/6308

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Re: [PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

Posted by "konstantinb (via GitHub)" <gi...@apache.org>.
konstantinb commented on PR #6308:
URL: https://github.com/apache/hive/pull/6308#issuecomment-4122190270

   closing in favor of https://github.com/apache/hive/pull/6359


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Re: [PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

Posted by "okumin (via GitHub)" <gi...@apache.org>.
okumin commented on code in PR #6308:
URL: https://github.com/apache/hive/pull/6308#discussion_r2922307064


##########
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFWhen.java:
##########
@@ -89,11 +96,23 @@ public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumen
             + "\" is expected but \"" + arguments[i + 1].getTypeName()
             + "\" is found");
       }
+      collectNonNullConstant(arguments[i + 1], distinctConstants);
     }
 
+    numberOfDistinctConstants = distinctConstants.size();
+
     return returnOIResolver.get();
   }
 
+  private static void collectNonNullConstant(ObjectInspector oi, Set<Object> distinctConstants) {
+    if (oi instanceof ConstantObjectInspector) {

Review Comment:
   @copilot Could you suggest a change that addresses this issue?
   https://sonarcloud.io/project/issues?sinceLeakPeriod=true&issueStatuses=OPEN%2CCONFIRMED&pullRequest=6308&id=apache_hive&open=AZzgJN8Un1Kc99ploZ32



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Re: [PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

Posted by "konstantinb (via GitHub)" <gi...@apache.org>.
konstantinb closed pull request #6308: HIVE-29368: limiting the NDV fix to the CASE clause handler only
URL: https://github.com/apache/hive/pull/6308


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Re: [PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

Posted by "konstantinb (via GitHub)" <gi...@apache.org>.
konstantinb commented on PR #6308:
URL: https://github.com/apache/hive/pull/6308#issuecomment-4051568941

   > From my perspective the improvement should land in `PessimisticStatCombiner` since `COALESCE`, and `IF` are also directly affected.
   > 
   > In addition, I feel that `PessimisticStatCombiner` is not working as expected when it comes to NDV. Taking the `max(NDV(branch_i))` is not really a pessimistic estimate.
   > 
   > A better formula for the estimation of NDV in CASE/Branch statements is:
   > 
   > ```
   > min(rows, Sum NDV(branch_i))
   > ```
   > 
   > This is formula is used by some other DBMS systems and should also handle this use-case with constant branches. We could also opt for more complex variants of the formula above taking into account the selectivity of the `WHEN` condition but we can leave that for future work.
   > 
   > All in all, I don't think we need to add additional bookeeping in the function itself but just modify the formula in `PessimisticStatCombiner`.
   
   @zabetak thank you very much for your comment.
   
   Changing PessimisticStatCombiner was my first idea too, however, the "truly pessimistic" estimate logic I used opened quite a large can of worms, broke many existing tests and has quickly ballooned to a rather big PR https://github.com/apache/hive/pull/6244
   (I admit that it did not, however, use your formula "min(rows, Sum NDV(branch_i))")
   
   While COALESCE and IF are, technically, affected in the same way, their "mis-estimations" are usually limited to 2x. The CASE with multiple constants was the most severe, and the code change of this PR has dramatically improved the situation in a private Hive implementation.


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Re: [PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

Posted by "okumin (via GitHub)" <gi...@apache.org>.
okumin commented on code in PR #6308:
URL: https://github.com/apache/hive/pull/6308#discussion_r2922307064


##########
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFWhen.java:
##########
@@ -89,11 +96,23 @@ public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumen
             + "\" is expected but \"" + arguments[i + 1].getTypeName()
             + "\" is found");
       }
+      collectNonNullConstant(arguments[i + 1], distinctConstants);
     }
 
+    numberOfDistinctConstants = distinctConstants.size();
+
     return returnOIResolver.get();
   }
 
+  private static void collectNonNullConstant(ObjectInspector oi, Set<Object> distinctConstants) {
+    if (oi instanceof ConstantObjectInspector) {

Review Comment:
   @copilot Could you suggest a change that addresses this issue?
   https://sonarcloud.io/project/issues?sinceLeakPeriod=true&issueStatuses=OPEN%2CCONFIRMED&pullRequest=6308&id=apache_hive&open=AZzgJN8Un1Kc99ploZ32



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Re: [PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

Posted by "konstantinb (via GitHub)" <gi...@apache.org>.
konstantinb commented on PR #6308:
URL: https://github.com/apache/hive/pull/6308#issuecomment-4053058164

   As it turns out, the fix for using "in(rows, Sum NDV(branch_i))" could require a very small code change; Checking how many tests https://github.com/apache/hive/pull/6359 will impact...


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Re: [PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

Posted by "konstantinb (via GitHub)" <gi...@apache.org>.
konstantinb commented on PR #6308:
URL: https://github.com/apache/hive/pull/6308#issuecomment-3930669180

   CC @okumin 


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Re: [PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

Posted by "sonarqubecloud[bot] (via GitHub)" <gi...@apache.org>.
sonarqubecloud[bot] commented on PR #6308:
URL: https://github.com/apache/hive/pull/6308#issuecomment-3874079768

   ## [![Quality Gate Passed](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/checks/QualityGateBadge/qg-passed-20px.png 'Quality Gate Passed')](https://sonarcloud.io/dashboard?id=apache_hive&pullRequest=6308) **Quality Gate passed**  
   Issues  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [2 New issues](https://sonarcloud.io/project/issues?id=apache_hive&pullRequest=6308&issueStatuses=OPEN,CONFIRMED&sinceLeakPeriod=true)  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/accepted-16px.png '') [0 Accepted issues](https://sonarcloud.io/project/issues?id=apache_hive&pullRequest=6308&issueStatuses=ACCEPTED)
   
   Measures  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [0 Security Hotspots](https://sonarcloud.io/project/security_hotspots?id=apache_hive&pullRequest=6308&issueStatuses=OPEN,CONFIRMED&sinceLeakPeriod=true)  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [0.0% Coverage on New Code](https://sonarcloud.io/component_measures?id=apache_hive&pullRequest=6308&metric=new_coverage&view=list)  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [0.0% Duplication on New Code](https://sonarcloud.io/component_measures?id=apache_hive&pullRequest=6308&metric=new_duplicated_lines_density&view=list)  
     
   [See analysis details on SonarQube Cloud](https://sonarcloud.io/dashboard?id=apache_hive&pullRequest=6308)
   
   


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Re: [PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

Posted by "okumin (via GitHub)" <gi...@apache.org>.
okumin commented on code in PR #6308:
URL: https://github.com/apache/hive/pull/6308#discussion_r2922409528


##########
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFWhen.java:
##########
@@ -89,11 +96,23 @@ public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumen
             + "\" is expected but \"" + arguments[i + 1].getTypeName()
             + "\" is found");
       }
+      collectNonNullConstant(arguments[i + 1], distinctConstants);
     }
 
+    numberOfDistinctConstants = distinctConstants.size();
+
     return returnOIResolver.get();
   }
 
+  private static void collectNonNullConstant(ObjectInspector oi, Set<Object> distinctConstants) {
+    if (oi instanceof ConstantObjectInspector) {
+      Object value = ((ConstantObjectInspector) oi).getWritableConstantValue();

Review Comment:
   Minor: https://sonarcloud.io/project/issues?sinceLeakPeriod=true&issueStatuses=OPEN%2CCONFIRMED&pullRequest=6308&id=apache_hive&open=AZzgJN8Un1Kc99ploZ32
   
   ```suggestion
       if (oi instanceof ConstantObjectInspector coi) {
         Object value = coi.getWritableConstantValue();
   ```



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Re: [PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

Posted by "sonarqubecloud[bot] (via GitHub)" <gi...@apache.org>.
sonarqubecloud[bot] commented on PR #6308:
URL: https://github.com/apache/hive/pull/6308#issuecomment-4043714243

   ## [![Quality Gate Passed](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/checks/QualityGateBadge/qg-passed-20px.png 'Quality Gate Passed')](https://sonarcloud.io/dashboard?id=apache_hive&pullRequest=6308) **Quality Gate passed**  
   Issues  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [2 New issues](https://sonarcloud.io/project/issues?id=apache_hive&pullRequest=6308&issueStatuses=OPEN,CONFIRMED&sinceLeakPeriod=true)  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/accepted-16px.png '') [0 Accepted issues](https://sonarcloud.io/project/issues?id=apache_hive&pullRequest=6308&issueStatuses=ACCEPTED)
   
   Measures  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [0 Security Hotspots](https://sonarcloud.io/project/security_hotspots?id=apache_hive&pullRequest=6308&issueStatuses=OPEN,CONFIRMED&sinceLeakPeriod=true)  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [0.0% Coverage on New Code](https://sonarcloud.io/component_measures?id=apache_hive&pullRequest=6308&metric=new_coverage&view=list)  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [0.0% Duplication on New Code](https://sonarcloud.io/component_measures?id=apache_hive&pullRequest=6308&metric=new_duplicated_lines_density&view=list)  
     
   [See analysis details on SonarQube Cloud](https://sonarcloud.io/dashboard?id=apache_hive&pullRequest=6308)
   
   


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Re: [PR] HIVE-29368: limiting the NDV fix to the CASE clause handler only [hive]

Posted by "sonarqubecloud[bot] (via GitHub)" <gi...@apache.org>.
sonarqubecloud[bot] commented on PR #6308:
URL: https://github.com/apache/hive/pull/6308#issuecomment-4044842682

   ## [![Quality Gate Passed](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/checks/QualityGateBadge/qg-passed-20px.png 'Quality Gate Passed')](https://sonarcloud.io/dashboard?id=apache_hive&pullRequest=6308) **Quality Gate passed**  
   Issues  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [1 New issue](https://sonarcloud.io/project/issues?id=apache_hive&pullRequest=6308&issueStatuses=OPEN,CONFIRMED&sinceLeakPeriod=true)  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/accepted-16px.png '') [0 Accepted issues](https://sonarcloud.io/project/issues?id=apache_hive&pullRequest=6308&issueStatuses=ACCEPTED)
   
   Measures  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [0 Security Hotspots](https://sonarcloud.io/project/security_hotspots?id=apache_hive&pullRequest=6308&issueStatuses=OPEN,CONFIRMED&sinceLeakPeriod=true)  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [0.0% Coverage on New Code](https://sonarcloud.io/component_measures?id=apache_hive&pullRequest=6308&metric=new_coverage&view=list)  
   ![](https://sonarsource.github.io/sonarcloud-github-static-resources/v2/common/passed-16px.png '') [0.0% Duplication on New Code](https://sonarcloud.io/component_measures?id=apache_hive&pullRequest=6308&metric=new_duplicated_lines_density&view=list)  
     
   [See analysis details on SonarQube Cloud](https://sonarcloud.io/dashboard?id=apache_hive&pullRequest=6308)
   
   


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