Hive QA commented on HIVE-14797:

Here are the results of testing the latest attachment:

{color:red}ERROR:{color} -1 due to no test(s) being added or modified.

{color:red}ERROR:{color} -1 due to 9 failed/errored test(s), 10592 tests 
*Failed tests:*
TestBeelineWithHS2ConnectionFile - did not produce a TEST-*.xml file (likely 
timed out) (batchId=197)
org.apache.hadoop.hive.cli.TestCliDriver.testCliDriver[order_null] (batchId=18)
org.apache.hive.beeline.TestBeelineArgParsing.testAddLocalJar[0] (batchId=155)
org.apache.hive.beeline.TestBeelineArgParsing.testAddLocalJar[1] (batchId=155)

Test results: https://builds.apache.org/job/PreCommit-HIVE-Build/1613/testReport
Console output: https://builds.apache.org/job/PreCommit-HIVE-Build/1613/console
Test logs:

Executing org.apache.hive.ptest.execution.TestCheckPhase
Executing org.apache.hive.ptest.execution.PrepPhase
Executing org.apache.hive.ptest.execution.ExecutionPhase
Executing org.apache.hive.ptest.execution.ReportingPhase
Tests exited with: TestsFailedException: 9 tests failed

This message is automatically generated.

ATTACHMENT ID: 12833869 - PreCommit-HIVE-Build

> reducer number estimating may lead to data skew
> -----------------------------------------------
>                 Key: HIVE-14797
>                 URL: https://issues.apache.org/jira/browse/HIVE-14797
>             Project: Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: roncenzhao
>            Assignee: roncenzhao
>         Attachments: HIVE-14797.2.patch, HIVE-14797.3.patch, 
> HIVE-14797.4.patch, HIVE-14797.patch
> HiveKey's hash code is generated by multipling by 31 key by key which is 
> implemented in method `ObjectInspectorUtils.getBucketHashCode()`:
> for (int i = 0; i < bucketFields.length; i++) {
>       int fieldHash = ObjectInspectorUtils.hashCode(bucketFields[i], 
> bucketFieldInspectors[i]);
>       hashCode = 31 * hashCode + fieldHash;
>     }
> The follow example will lead to data skew:
> I hava two table called tbl1 and tbl2 and they have the same column: a int, b 
> string. The values of column 'a' in both two tables are not skew, but values 
> of column 'b' in both two tables are skew.
> When my sql is "select * from tbl1 join tbl2 on tbl1.a=tbl2.a and 
> tbl1.b=tbl2.b" and the estimated reducer number is 31, it will lead to data 
> skew.
> As we know, the HiveKey's hash code is generated by `hash(a)*31 + hash(b)`. 
> When reducer number is 31 the reducer No. of each row is `hash(b)%31`. In the 
> result, the job will be skew.

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