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https://issues.apache.org/jira/browse/SOLR-13234?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16790020#comment-16790020
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Danyal Prout commented on SOLR-13234:
-------------------------------------
Sorry for the delay in looking at this. Just pushed a PR which fixes this test
case here:
[https://github.com/apache/lucene-solr/pull/605]
It was due to the Prometheus label "terminated" in the test not being
localized, but the label from Solr being localized to "termınated" {{}} on a
JVM with Turkish locale. I've removed checking the actual label as these could
change based on JVM config and instead checked that we get the correct number
of labels back for JVM thread settings (which I think is potentially a more
complete test).
> Prometheus Metric Exporter Not Threadsafe
> -----------------------------------------
>
> Key: SOLR-13234
> URL: https://issues.apache.org/jira/browse/SOLR-13234
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Components: metrics
> Affects Versions: 7.6, 8.0
> Reporter: Danyal Prout
> Assignee: Shalin Shekhar Mangar
> Priority: Minor
> Labels: metric-collector
> Fix For: 8.x, master (9.0)
>
> Attachments: SOLR-13234-branch_7x.patch
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> The Solr Prometheus Exporter collects metrics when it receives a HTTP request
> from Prometheus. Prometheus sends this request, on its [scrape
> interval|https://prometheus.io/docs/prometheus/latest/configuration/configuration/#scrape_config].
> When the time taken to collect the Solr metrics is greater than the scrape
> interval of the Prometheus server, this results in concurrent metric
> collection occurring in this
> [method|https://github.com/apache/lucene-solr/blob/master/solr/contrib/prometheus-exporter/src/java/org/apache/solr/prometheus/collector/SolrCollector.java#L86].
> This method doesn’t appear to be thread safe, for instance you could have
> concurrent modifications of a
> [map|https://github.com/apache/lucene-solr/blob/master/solr/contrib/prometheus-exporter/src/java/org/apache/solr/prometheus/collector/SolrCollector.java#L119].
> After a while the Solr Exporter processes becomes nondeterministic, we've
> observed NPE and loss of metrics.
> To address this, I'm proposing the following fixes:
> 1. Read/parse the configuration at startup and make it immutable.
> 2. Collect metrics from Solr on an interval which is controlled by the Solr
> Exporter and cache the metric samples to return during Prometheus scraping.
> Metric collection can be expensive, for example executing arbitrary Solr
> searches, it's not ideal to allow for concurrent metric collection and on an
> interval which is not defined by the Solr Exporter.
> There are also a few other performance improvements that we've made while
> fixing this, for example using the ClusterStateProvider instead of sending
> multiple HTTP requests to each Solr node to lookup all the cores.
> I'm currently finishing up these changes which I'll submit as a PR.
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