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https://issues.apache.org/jira/browse/HADOOP-12529?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14984176#comment-14984176
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Chris Nauroth commented on HADOOP-12529:
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[~vinayrpet], I think in order to proceed with an optimization like that, we'd
need to do an exhaustive review of both Hadoop and downstream ecosystem
projects to check if they use any mutable operations on an instance returned
from {{UserGroupInformation#createProxyUser}}. Existing calls to {{addToken}}
or {{addCredentials}} on a proxy user would make it difficult to proceed safely.
Interestingly, while browsing around, I noticed that Oozie maintains a cache of
proxy user instances, perhaps for this very reason. The class is
{{org.apache.oozie.service.UserGroupInformationService}}. This might imply
that caching of proxy users is better handled as an application-specific
concern, where that application knows the full lifecycle and usage of those
instances, instead of at the core where we don't have that knowledge.
> UserGroupInformation equals method depend on the subject object address
> -----------------------------------------------------------------------
>
> Key: HADOOP-12529
> URL: https://issues.apache.org/jira/browse/HADOOP-12529
> Project: Hadoop Common
> Issue Type: Bug
> Components: security
> Affects Versions: 2.7.1
> Reporter: wangwenli
>
> my question is why UserGroupInformation equals method depend on the
> subject object?
> try below code which is extract from HiveMetaStore:
> {code:title=TestUgi.java|borderStyle=solid}
> UserGroupInformation clientUgi = null;
> UserGroupInformation clientUgi2 = null;
> try {
> clientUgi = UserGroupInformation.createProxyUser("user2",
> UserGroupInformation.getLoginUser());
> clientUgi2 = UserGroupInformation.createProxyUser("user2",
> UserGroupInformation.getLoginUser());
> if (clientUgi.equals(clientUgi2)) {
> System.out.println("==");
> } else {
> System.out.println("!="); // strangely this will be hit
> }
> } catch (IOException e1) {
> e1.printStackTrace();
> }
> {code}
> i found that it is because the equal method from UserGroupInformation
> is compare on subject object ref : subject == ((UserGroupInformation)
> o).subject; .
> as you know, ipc.Client connect to namenode,
> connections.get(ConnectionId) this code will try to reuse the same socket
> to namenode, but because of ConnectionId's equal depend on ugi equal, which
> will cause connections.get(ConnectionId) cann't get the same socket,
> suppose many connect to HiveMetaStore, then many connection to Namenode will
> established.
> so my doubts is why UserGroupInformation is compare on subject object
> ref : subject == ((UserGroupInformation) o).subject, it should compare on
> subject's principal, am i right?
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