Misha Dmitriev created YARN-7386:
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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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