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From "Misha Dmitriev (JIRA)" <j...@apache.org>
Subject [jira] [Created] (YARN-7386) Duplicate Strings in various places in Yarn memory
Date Tue, 24 Oct 2017 20:19:02 GMT
Misha Dmitriev created YARN-7386:
------------------------------------

             Summary: Duplicate Strings in various places in Yarn memory
                 Key: YARN-7386
                 URL: https://issues.apache.org/jira/browse/YARN-7386
             Project: Hadoop YARN
          Issue Type: Improvement
            Reporter: Misha Dmitriev
            Assignee: Misha Dmitriev


Using jxray (www.jxray.com) I've analyzed a Yarn RM heap dump obtained in a big cluster. The
tool uncovered several sources of memory waste. One problem is duplicate strings:

{code}
Total strings 	  Unique strings 	  Duplicate values 	 Overhead 
 361,506	 86,672	 5,928	22,886K (7.6%)
{code}

They are spread across a number of locations. The biggest source of waste is the following
reference chain:

{code}

7,416K (2.5%), 31292 / 62% dup strings (499 unique), 31292 dup backing arrays:
↖{j.u.HashMap}.values
↖org.apache.hadoop.yarn.api.records.impl.pb.ContainerLaunchContextPBImpl.environment
↖org.apache.hadoop.yarn.api.records.impl.pb.ApplicationSubmissionContextPBImpl.amContainer
↖org.apache.hadoop.yarn.server.resourcemanager.rmapp.RMAppImpl.submissionContext
↖{java.util.concurrent.ConcurrentHashMap}.values
↖org.apache.hadoop.yarn.server.resourcemanager.RMActiveServiceContext.applications
↖org.apache.hadoop.yarn.server.resourcemanager.RMContextImpl.activeServiceContext
↖org.apache.hadoop.yarn.server.resourcemanager.rmapp.monitor.RMAppLifetimeMonitor.rmContext
↖Java Local@3ed9ef820 (org.apache.hadoop.yarn.server.resourcemanager.rmapp.monitor.RMAppLifetimeMonitor)
{code}

However, there are also many others. Mostly they are strings in proto buffer or proto buffer
builder objects. I plan to get rid of at least the worst offenders by inserting String.intern()
calls. String.intern() used to consume memory in PermGen and was not very scalable up until
about the early JDK 7 versions, but has greatly improved since then, and I've used it many
times without any issues.



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