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https://issues.apache.org/jira/browse/HADOOP-11402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14259167#comment-14259167
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Benoy Antony commented on HADOOP-11402:
---------------------------------------

Since the negativeCacheTimeout is already specified while building the cache, 
there is no benefit in storing expirationTime in each cache entry.
Instead, is it possible to keep it as a Set ?

An untested code snippet is below
 {code}
                  Set<String> negativeCache;
                 Cache<String, Boolean> negativeCacheMap = 
CacheBuilder.newBuilder()
                                         
.expireAfterWrite(negativeCacheTimeout, TimeUnit.MILLISECONDS)
                                         .ticker(new 
TimerToTickerAdapter(timer))
                                         .build();
                 negativeCache = 
Collections.newSetFromMap(negativeCache.asMap());
{code}

> Use guava cache to implement negative user-to-group cache
> ---------------------------------------------------------
>
>                 Key: HADOOP-11402
>                 URL: https://issues.apache.org/jira/browse/HADOOP-11402
>             Project: Hadoop Common
>          Issue Type: Improvement
>    Affects Versions: 2.6.0
>            Reporter: Colin Patrick McCabe
>            Assignee: Varun Saxena
>         Attachments: HADOOP-11402.001.patch, HADOOP-11402.002.patch
>
>
> Negative user-to-group cache entries are never cleared for 
> never-again-accessed users.  Use guava cache so that expired entries can be 
> deleted automatically



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