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https://issues.apache.org/jira/browse/SOLR-14657?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17166366#comment-17166366
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Andrzej Bialecki commented on SOLR-14657:
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The same issue is present in a few other components, eg.
SolrCore.initializeMetrics, although there I opted for checking whether the
core is closed ... how about adding this convenience method as
{{SolrMetricsContext.safeGauge(Gauge g, Object defValue) /
}}{{SolrMetricsContext.safeGauge(Gauge g)}} ? At least we would have one
central place to make these decisions. For this particular gauge I would be
tempted to return -1 instead of null, as a kind of "impossible value" that we
already return from other numeric gauges.
The {{MetricsHandler}} (or more precisely {{MetricUtils}}) knows how to handle
null output from Gauges, it's simply translated to a null JSON value. Whether
that's better than a fake value is another discussion, see SOLR-14683 - some
clients may not be prepared to deal with {{null}} JSON values. Perhaps such
values should not appear at all in the metrics output?
Anyway, in this issue we can at least refactor the code to make that decision
easier.
> spurious ERRORs due to race condition between SolrIndexSearcher metrics and
> IndexReader closing
> -----------------------------------------------------------------------------------------------
>
> Key: SOLR-14657
> URL: https://issues.apache.org/jira/browse/SOLR-14657
> Project: Solr
> Issue Type: Improvement
> Security Level: Public(Default Security Level. Issues are Public)
> Reporter: Chris M. Hostetter
> Assignee: Chris M. Hostetter
> Priority: Major
> Attachments: SOLR-14657.patch
>
>
> I've seen situations in the wild where systems monitoring/polling metrics can
> trigger scary looking - but otherwise benign - ERRORs due to
> AlreadyClosedExceptions if/when the searcher/reader is in the process of
> being re-opened and the Gauge tries to call reader.numDocs(), etc...
> We should tweak the metrics logic to just ignore these exceptions
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