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https://issues.apache.org/jira/browse/HIVE-14797?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15509958#comment-15509958
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Hive QA commented on HIVE-14797:
--------------------------------
Here are the results of testing the latest attachment:
https://issues.apache.org/jira/secure/attachment/12829560/HIVE-14797.2.patch
{color:red}ERROR:{color} -1 due to no test(s) being added or modified.
{color:red}ERROR:{color} -1 due to 7 failed/errored test(s), 10526 tests
executed
*Failed tests:*
{noformat}
TestMiniLlapCliDriver-auto_sortmerge_join_13.q-tez_dynpart_hashjoin_1.q-schema_evol_orc_acidvec_table_update.q-and-27-more
- did not produce a TEST-*.xml file
org.apache.hadoop.hive.cli.TestCliDriver.testCliDriver[acid_mapjoin]
org.apache.hadoop.hive.cli.TestCliDriver.testCliDriver[ctas]
org.apache.hadoop.hive.cli.TestCliDriver.testCliDriver[vector_join_part_col_char]
org.apache.hadoop.hive.cli.TestMiniTezCliDriver.testCliDriver[explainuser_3]
org.apache.hadoop.hive.metastore.TestMetaStoreMetrics.testMetaDataCounts
org.apache.hive.jdbc.TestJdbcWithMiniHS2.testAddJarConstructorUnCaching
{noformat}
Test results: https://builds.apache.org/job/PreCommit-HIVE-Build/1252/testReport
Console output: https://builds.apache.org/job/PreCommit-HIVE-Build/1252/console
Test logs:
http://ec2-204-236-174-241.us-west-1.compute.amazonaws.com/logs/PreCommit-HIVE-Build-1252/
Messages:
{noformat}
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: 7 tests failed
{noformat}
This message is automatically generated.
ATTACHMENT ID: 12829560 - 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.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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