[HADOOP-11301] [optionally] update jmx cache to drop old metrics

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.7.0, 2.6.5
• Hadoop Flags: Reviewed
• Assignee: Maysam Yabandeh
• Reporter: Maysam Yabandeh
• Created: 12/Nov/14 23:48
• Updated: 14/Sep/16 03:58
• Resolved: 02/Dec/14 07:13

Description

MetricsSourceAdapter::updateJmxCache() skips updating the info cache if no new metric is added since last time:

      int oldCacheSize = attrCache.size();
      int newCacheSize = updateAttrCache();
      if (oldCacheSize < newCacheSize) {
        updateInfoCache();
      }

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.

Issue Links

• relates to: HDFS-6982 nntop: top­-like tool for name node users