[jira] [Created] (YARN-7320) Duplicate LiteralByteStrings in SystemCredentialsForAppsProto.credentialsForApp_

["Misha Dmitriev (JIRA)" <ji...@apache.org>]

Misha Dmitriev created YARN-7320:
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             Summary: Duplicate LiteralByteStrings in SystemCredentialsForAppsProto.credentialsForApp_
                 Key: YARN-7320
                 URL: https://issues.apache.org/jira/browse/YARN-7320
             Project: Hadoop YARN
          Issue Type: Improvement
            Reporter: Misha Dmitriev


Using jxray (www.jxray.com) I've analyzed several heap dumps from YARN Resource Manager running in a big cluster. The tool uncovered several sources of memory waste. One problem, which results in wasting more than a quarter of all memory, is a large number of duplicate {{LiteralByteString}} objects coming from the following reference chain:

{code}
1,011,810K (26.9%): byte[]: 5416705 / 100% dup arrays (22108 unique)
↖com.google.protobuf.LiteralByteString.bytes
↖org.apache.hadoop.yarn.proto.YarnServerCommonServiceProtos$.credentialsForApp_
↖{j.u.ArrayList}
↖j.u.Collections$UnmodifiableRandomAccessList.c
↖org.apache.hadoop.yarn.proto.YarnServerCommonServiceProtos$NodeHeartbeatResponseProto.systemCredentialsForApps_
↖org.apache.hadoop.yarn.server.api.protocolrecords.impl.pb.NodeHeartbeatResponsePBImpl.proto
↖org.apache.hadoop.yarn.server.resourcemanager.rmnode.RMNodeImpl.latestNodeHeartBeatResponse
↖org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.FSSchedulerNode.rmNode
...
{code}

That is, collectively reference chains that look as above hold in memory 5.4 million {{LiteralByteString}} objects, but only ~22 thousand of these objects are unique. Deduplicating these objects, e.g. using a Google Object Interner instance, would save ~1GB of memory.

It looks like the main place where the above {{LiteralByteString}}s are created and attached to the {{SystemCredentialsForAppsProto}} objects is in {{NodeHeartbeatResponsePBImpl.java}}, method {{addSystemCredentialsToProto()}}. Probably adding a call to an interner there will fix the problem. wi 



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