Launch reduces only after a few maps have run in the Fair Scheduler

• Key: HADOOP-4666
• Type: Improvement
• Status: Closed
• Resolution: Fixed
• Priority: Major
• Assignee: Matei Zaharia
• Reporter: Matei Zaharia
• Fix Version/s: 0.20.0

Description

It makes no sense to schedule reduces for a job before its maps have started running. As an initial fix, we will wait until a certain percent have run (likely 10%). In the future it would be good to choose the time to wait based on amount of map output data as well - launching reducers that will mostly be idle is not helpful. Average amount of map output bytes per mapper is easy to compute using counters in JobInProgress.

Comments

[Matei Zaharia]

Here is a patch for this issue that waits for at least 5% of maps to be launched, as will be happening in HADOOP-3136. (Patch also includes some minor formatting fixes.)

[dhruba borthakur]

+1. Code looks good.

[Hadoop QA]

-1 overall. Here are the results of testing the latest attachment
http://issues.apache.org/jira/secure/attachment/12394462/fairscheduler-reduce-launch-condition.patch
against trunk revision 719787.

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

+1 tests included. The patch appears to include 5 new or modified tests.

+1 javadoc. The javadoc tool did not generate any 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 Eclipse classpath. The patch retains Eclipse classpath integrity.

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

+1 contrib tests. The patch passed contrib unit tests.

Test results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3637/testReport/
Findbugs warnings: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3637/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Checkstyle results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3637/artifact/trunk/build/test/checkstyle-errors.html
Console output: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3637/console

This message is automatically generated.

[Johan Oskarsson]

I just committed this. Thanks Matei!

[Johan Oskarsson]

The tests failures were not related to the patch. I've created this issue for one of them that I've seen time out in a few other patch runs. HADOOP-4716

[Matei Zaharia]

Thanks Johan for the quick commit.

[Hudson]

Integrated in Hadoop-trunk #670 (See http://hudson.zones.apache.org/hudson/job/Hadoop-trunk/670/)
. Launch reduces only after a few maps have run in the Fair Scheduler. (Matei Zaharia via johan)