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From "Jitendra Nath Pandey (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8088) User-group mapping cache incorrectly does negative caching on transient failures
Date Fri, 16 Mar 2012 20:17:40 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8088?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13231583#comment-13231583
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Jitendra Nath Pandey commented on HADOOP-8088:
----------------------------------------------

I agree with devaraj's proposal. Too many queries for a non-existent user should happen only
in case of a security attack, but authentication should prevent any rogue user if security
is enabled. 
                
> User-group mapping cache incorrectly does negative caching on transient failures
> --------------------------------------------------------------------------------
>
>                 Key: HADOOP-8088
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8088
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: security
>    Affects Versions: 0.20.205.0, 0.24.0, 0.23.1, 1.0.0, 1.1.0
>            Reporter: Kihwal Lee
>             Fix For: 0.24.0, 1.1.0, 0.23.2
>
>         Attachments: hadoop-8088-branch-1.patch, hadoop-8088-trunk.patch, hadoop-8088-trunk.patch
>
>
> We've seen a case where some getGroups() calls fail when the ldap server or the network
is having transient failures. Looking at the code, the shell-based and the JNI-based implementations
swallow exceptions and return an empty or partial list. The caller, Groups#getGroups() adds
this likely empty list into the mapping cache for the user. This will function as negative
caching until the cache expires. I don't think we want negative caching here, but even if
we do, it should be intelligent enough to distinguish transient failures from ENOENT. The
log message in the jni-based impl also needs an improvement. It should print what exception
it encountered instead of just saying one happened.

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