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https://issues.apache.org/jira/browse/HADOOP-11301?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14221602#comment-14221602
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Maysam Yabandeh commented on HADOOP-11301:
------------------------------------------
[~stack], this test requires updateAttrCache to be invoked upon each
updateJmxCache call.
{code}
public void testGetMetricsAndJmx() throws Exception {
...
Thread.sleep(100); // skip JMX cache TTL
assertEquals(0L, (Number)sa.getAttribute("C1"));
{code}
At this point I am not sure whether the rest of hadoop depends on this or the
unit test demands are broader than what the users of jmx actually need. A safer
option is to preserve backward compatibility and invoke updateAttrCache all the
time. Let me know your thoughts on this.
> [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
> Attachments: HADOOP-11301.v01.patch, HADOOP-11301.v02.patch,
> HADOOP-11301.v03.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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