[
https://issues.apache.org/jira/browse/HADOOP-11301?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14221637#comment-14221637
]
Maysam Yabandeh commented on HADOOP-11301:
------------------------------------------
Sure. I have to admit the the logic behind updateJmxCache is a bit confusing
for me and it is not very clear for me that when the cache was intended to be
updated. To reconstruct the expected contract, which is missing in the code,
one would need to review all the usages inside the hadoop project. It seems
that jmx meant to update the metrics with a frequency less then or equal to
2*jmxCacheTTL.
As you suggested I will upload a patch with the conservative approach of
keeping the current implementation backward compatible with previous unit
tests.
> [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.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
