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From "Hive QA (JIRA)" <>
Subject [jira] [Commented] (HIVE-15796) HoS: poor reducer parallelism when operator stats are not accurate
Date Wed, 08 Feb 2017 11:01:41 GMT


Hive QA commented on HIVE-15796:

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 7 failed/errored test(s), 10241 tests executed
*Failed tests:*
TestDerbyConnector - did not produce a TEST-*.xml file (likely timed out) (batchId=235)
org.apache.hadoop.hive.cli.TestMiniLlapLocalCliDriver.testCliDriver[vector_if_expr] (batchId=140)
org.apache.hadoop.hive.cli.TestPerfCliDriver.testCliDriver[query14] (batchId=223)
org.apache.hadoop.hive.cli.TestPerfCliDriver.testCliDriver[query23] (batchId=223)
org.apache.hadoop.hive.cli.TestSparkCliDriver.testCliDriver[cross_product_check_2] (batchId=133)
org.apache.hadoop.hive.cli.TestSparkCliDriver.testCliDriver[union15] (batchId=133)

Test results:
Console output:
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: 7 tests failed

This message is automatically generated.

ATTACHMENT ID: 12851582 - PreCommit-HIVE-Build

> HoS: poor reducer parallelism when operator stats are not accurate
> ------------------------------------------------------------------
>                 Key: HIVE-15796
>                 URL:
>             Project: Hive
>          Issue Type: Improvement
>          Components: Statistics
>    Affects Versions: 2.2.0
>            Reporter: Chao Sun
>            Assignee: Chao Sun
>         Attachments: HIVE-15796.1.patch, HIVE-15796.wip.1.patch, HIVE-15796.wip.2.patch,
> In HoS we use currently use operator stats to determine reducer parallelism. However,
it is often the case that operator stats are not accurate, especially if column stats are
not available. This sometimes will generate extremely poor reducer parallelism, and cause
HoS query to run forever. 
> This JIRA tries to offer an alternative way to compute reducer parallelism, similar to
how MR does. Here's the approach we are suggesting:
> 1. when computing the parallelism for a MapWork, use stats associated with the TableScan
> 2. when computing the parallelism for a ReduceWork, use the *maximum* parallelism from
all its parents.

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