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From "Andrzej Bialecki (JIRA)" <>
Subject [jira] [Updated] (SOLR-11221) SolrJmxReporter broken on core reload
Date Sat, 12 Aug 2017 00:12:00 GMT


Andrzej Bialecki  updated SOLR-11221:
    Attachment: SOLR-11221.patch

This patch changes {{SolrJmxReporter}} so that it uses a modified version of {{JmxReporter}},
which adds an "_instanceTag" attribute to track what beans it had registered and unregisters
only those. In a sense this is the same mechanism that {{JmxMonitoredMap}} used, only it was
called {{coreHashCode}} there (we can call it the same if it gives users a sense of familiarity,
but I thought the "_instanceTag" name is harder to mistake for a real bean attribute).

The new unit test passes with this change, while it was failing with the old implementation.
Manual testing with JConsole also shows that metrics are now correctly reported in local and
cloud mode, and after core and collection reloads.

This is unfortunately a bigger change than I hoped for, so I'm not sure whether this should
go into 7.0 at such late stage in the release. OTOH JMX monitoring is surely broken without
this change, so it can't get much worse ;)

> SolrJmxReporter broken on core reload
> -------------------------------------
>                 Key: SOLR-11221
>                 URL:
>             Project: Solr
>          Issue Type: Bug
>      Security Level: Public(Default Security Level. Issues are Public) 
>          Components: metrics
>    Affects Versions: 6.6, 7.0, 6.7, master (8.0)
>            Reporter: Andrzej Bialecki 
>            Assignee: Andrzej Bialecki 
>            Priority: Critical
>         Attachments: SOLR-11221.patch
> {{SolrJmxReporter}} uses Dropwizard's {{JmxReporter}}, which in turn uses a {{MetricRegistry}}
listener to report newly added metrics as MBeans, and to unregister them from MBeanServer
when the reporter is closed, which happens when core is closed.
> The metrics API keeps around existing metrics in {{solr.core.*}} registries to help maintain
continuous metrics in presence of core reloads. However, this means that some of these metric
instances are not registered anew when a core is reloaded - and for these metrics the listener
won't fire, so the MBeans won't be registered.
> This limitation is a result of the use of {{MetricRegistryListener}} in {{JmxReporter}}
and can't be fixed without reimplementing this class. Another possible approach would be to
configure the {{JmxReporter}} to use a "mirroring" registry instead, which will be populated
with existing metrics from the original registry (thus generating "metric added" events) and
then kept in sync with the main registry via a listener.

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