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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-10755) Support negative caching of user-group mapping
Date Mon, 21 Jul 2014 18:26:40 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-10755?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14068985#comment-14068985

Andrew Wang commented on HADOOP-10755:

Good idea with the Timer. Few comments, otherwise +1 though:

* Could we make Timer into an interface, and have nested classes DefaultTimer and FakeTimer?
These are all tiny, so can just keep them in the same file.
* We can just make Time InterfaceAudience.Private. I think saying LimitedPrivate HDFS and
MapReduce is the same as Private, so doesn't make much sense.
* Timer class javadoc, typo "override" to "overridden"
* FakeTimer, would say that it's for test purposes rather than "as dependency injections"
(not grammatical)
* In the new test, let's fill in the {{fail()}} and empty catches with messages and asserts.
Take a look at GenericTestUtils.assertExceptionContains.

> Support negative caching of user-group mapping
> ----------------------------------------------
>                 Key: HADOOP-10755
>                 URL: https://issues.apache.org/jira/browse/HADOOP-10755
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: security
>    Affects Versions: 2.2.0
>            Reporter: Andrew Wang
>            Assignee: Lei (Eddy) Xu
>         Attachments: HADOOP-10755.000.patch, HADOOP-10755.001.patch, HADOOP-10755.002.patch,
HADOOP-10755.003.patch, HDFS-5369.000.patch
> We've seen a situation at a couple of our customers where interactions from an unknown
user leads to a high-rate of group mapping calls. In one case, this was happening at a rate
of 450 calls per second with the shell-based group mapping, enough to severely impact overall
namenode performance and also leading to large amounts of log spam (prints a stack trace each
> Let's consider negative caching of group mapping, as well as quashing the rate of this
log message.

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