Reduce often attempts in memory merge with no work

• Key: HADOOP-3940
• Type: Bug
• Status: Closed
• Resolution: Fixed
• Priority: Minor
• Assignee: Chris Douglas
• Reporter: Chris Douglas
• Affects Version/s: 0.18.0
• Fix Version/s: 0.18.1

Description

ReduceTask.ReduceCopier.ShuffleRamManager initializes numRequiredMapOutputs to 0, so one of the predicates in ShuffleRamManager::waitForDataToMerge, numPendingRequests < numRequiredMapOutputs, is false until the first map output is fetched and false again after the last map output is fetched. The InMemFSMergeThread thread will loop busily in this state.

Comments

[Chris Douglas]

Simplest fix, waiting on numRequiredMapOutputs == 0.

Initializing numRequiredMapOutputs to Integer.MAX_VALUE would require a different check at the end; this should handle both.

[Chris Douglas]

[ edit - nevermind ]

[Hadoop QA]

-1 overall. Here are the results of testing the latest attachment
http://issues.apache.org/jira/secure/attachment/12388084/3940-0.patch
against trunk revision 685425.

+1 @author. The patch does not contain any @author tags.

-1 tests included. The patch doesn't appear to include any new or modified tests.
Please justify why no tests are needed for this patch.

-1 javadoc. The javadoc tool appears to have generated 1 warning messages.

+1 javac. The applied patch does not increase the total number of javac compiler warnings.

+1 findbugs. The patch does not introduce any new Findbugs warnings.

+1 release audit. The applied patch does not increase the total number of release audit warnings.

-1 core tests. The patch failed core unit tests.

-1 contrib tests. The patch failed contrib unit tests.

Test results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3058/testReport/
Findbugs warnings: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3058/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Checkstyle results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3058/artifact/trunk/build/test/checkstyle-errors.html
Console output: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3058/console

This message is automatically generated.

[Chris Douglas]

Added some comments to waitForDataToMerge, particularly explaining why numRequiredMapOutputs == 0 is a special case, per Arun's suggestion.

Test failures are due to HADOOP-3946.

[Arun C Murthy]

+1

[Chris Douglas]

I just committed this

[Hudson]

Integrated in Hadoop-trunk #581 (See http://hudson.zones.apache.org/hudson/job/Hadoop-trunk/581/)

[Owen O'Malley]

There was a suggestion on the list to include this in 0.18.1. That sounds right to me. Thoughts?

[Chris Douglas]

+1

Merged into 0.18 branch

[Hudson]

Integrated in Hadoop-trunk #595 (See http://hudson.zones.apache.org/hudson/job/Hadoop-trunk/595/)