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From "Stephen O'Donnell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-13263) Reload cached groups in background after expiry
Date Wed, 22 Jun 2016 12:58:57 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13263?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15344271#comment-15344271
] 

Stephen O'Donnell commented on HADOOP-13263:
--------------------------------------------

[~arpitagarwal] I got the style issues sorted, and I also removed the synchronized block that
was causing problems with find bugs and put it into the class constructor. Not sure why I
didn't do that originally, as I think that is the best place for it. All my tests pass locally
and from the last Hadoop QA run it seems there is only 1 test failure that appears to be unrelated
to this patch:

{code}
Tests run: 2, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0.551 sec <<< FAILURE!
- in org.apache.hadoop.metrics2.impl.TestGangliaMetrics
testGangliaMetrics2(org.apache.hadoop.metrics2.impl.TestGangliaMetrics)  Time elapsed: 0.327
sec  <<< FAILURE!
java.lang.AssertionError: Missing metrics: test.s1rec.Xxx
	at org.junit.Assert.fail(Assert.java:88)
	at org.junit.Assert.assertTrue(Assert.java:41)
	at org.apache.hadoop.metrics2.impl.TestGangliaMetrics.checkMetrics(TestGangliaMetrics.java:161)
	at org.apache.hadoop.metrics2.impl.TestGangliaMetrics.testGangliaMetrics2(TestGangliaMetrics.java:139)
{code}

Assuming you are happy with the initialization of the executor happening in the constructor
I think this one is complete.

Do we need to raise a documentation jira to mentioned the new parameters to enable the feature?
You also mentioned an additional jira to remove delays from the tests, making them more robust.
Some of the original tests had delays in them too, so that is something that should look over
that entire test class I guess.

> Reload cached groups in background after expiry
> -----------------------------------------------
>
>                 Key: HADOOP-13263
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13263
>             Project: Hadoop Common
>          Issue Type: Improvement
>            Reporter: Stephen O'Donnell
>            Assignee: Stephen O'Donnell
>         Attachments: HADOOP-13263.001.patch, HADOOP-13263.002.patch, HADOOP-13263.003.patch,
HADOOP-13263.004.patch, HADOOP-13263.005.patch, HADOOP-13263.006.patch
>
>
> In HADOOP-11238 the Guava cache was introduced to allow refreshes on the Namenode group
cache to run in the background, avoiding many slow group lookups. Even with this change, I
have seen quite a few clusters with issues due to slow group lookups. The problem is most
prevalent in HA clusters, where a slow group lookup on the hdfs user can fail to return for
over 45 seconds causing the Failover Controller to kill it.
> The way the current Guava cache implementation works is approximately:
> 1) On initial load, the first thread to request groups for a given user blocks until
it returns. Any subsequent threads requesting that user block until that first thread populates
the cache.
> 2) When the key expires, the first thread to hit the cache after expiry blocks. While
it is blocked, other threads will return the old value.
> I feel it is this blocking thread that still gives the Namenode issues on slow group
lookups. If the call from the FC is the one that blocks and lookups are slow, if can cause
the NN to be killed.
> Guava has the ability to refresh expired keys completely in the background, where the
first thread that hits an expired key schedules a background cache reload, but still returns
the old value. Then the cache is eventually updated. This patch introduces this background
reload feature. There are two new parameters:
> 1) hadoop.security.groups.cache.background.reload - default false to keep the current
behaviour. Set to true to enable a small thread pool and background refresh for expired keys
> 2) hadoop.security.groups.cache.background.reload.threads - only relevant if the above
is set to true. Controls how many threads are in the background refresh pool. Default is 1,
which is likely to be enough.



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