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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-11301) [optionally] update jmx cache to drop old metrics
Date Tue, 02 Dec 2014 18:39:13 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-11301?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14231887#comment-14231887
] 

stack commented on HADOOP-11301:
--------------------------------

Just to say that this patch also fixes an issue in hbase where when a region is deleted (split
or table removed), metrics would get stuck reporting the last state of metrics on the removed
region; metrics was showing 'ghosts'. Thanks [~maysamyabandeh]

> [optionally] update jmx cache to drop old metrics
> -------------------------------------------------
>
>                 Key: HADOOP-11301
>                 URL: https://issues.apache.org/jira/browse/HADOOP-11301
>             Project: Hadoop Common
>          Issue Type: Improvement
>            Reporter: Maysam Yabandeh
>            Assignee: Maysam Yabandeh
>             Fix For: 2.7.0
>
>         Attachments: HADOOP-11301.v01.patch, HADOOP-11301.v02.patch, HADOOP-11301.v03.patch,
HADOOP-11301.v04.patch
>
>
> MetricsSourceAdapter::updateJmxCache() skips updating the info cache if no new metric
is added since last time:
> {code}
>       int oldCacheSize = attrCache.size();
>       int newCacheSize = updateAttrCache();
>       if (oldCacheSize < newCacheSize) {
>         updateInfoCache();
>       }
> {code}
> This behavior is not desirable in some applications. For example nntop (HDFS-6982) reports
the top users via jmx. The list is updated after each report. The previously reported top
users hence should be removed from the cache upon each report request.
> In our production run of nntop we made a change to ignore the size check and always perform
updateInfoCache. I am planning to submit a patch including this change. The feature can be
enabled by a configuration parameter.



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