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Posted to dev@lucene.apache.org by "Jeff Wartes (JIRA)" <ji...@apache.org> on 2015/12/11 23:08:46 UTC
[jira] [Commented] (SOLR-4449) Enable backup requests for the
internal solr load balancer
[ https://issues.apache.org/jira/browse/SOLR-4449?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15053665#comment-15053665 ]
Jeff Wartes commented on SOLR-4449:
-----------------------------------
I looked around a bit, and unless I'm missing something, it looks like solr-core doesn't really use metrics-core. At the end of SOLR-1972, the necessary classes were just copy/pasted into the solr codeline. It sounds like this was mostly due to being nervous after encountering some problems in the metrics-core version at the time, and an aversion to a global registry approach.
Unfortunately, this means that although requesthandlers have statistics, they cannot be attached to a metrics Reporter, and instead you have to develop something to interrogate JMX or some such.
Solr does include metrics-core 3.0.1, but there's only a few places it actually gets used, and only in contrib modules.
I didn't have the negative experience with metrics-core. In fact, my experiences with 3.1.2 over the last year and a half has been universally positive. So when I added backup-percentile support to this issue I relied heavily on the global SharedMetricsRegistry and the assumption that the library was threadsafe in general. My scattershot code reviews of the metrics library have generally enforced my opinion that this is ok, and I'm using my version of this issue in production now. Initializing a well-known-named shared registry with an attached reporter in jetty.xml has yielded all kinds of great performance data.
This might be a useful point of information if anyone gets back to SOLR-4735. I'll mention here if I do encounter any metrics-core related issues in the future.
> Enable backup requests for the internal solr load balancer
> ----------------------------------------------------------
>
> Key: SOLR-4449
> URL: https://issues.apache.org/jira/browse/SOLR-4449
> Project: Solr
> Issue Type: New Feature
> Components: SolrCloud
> Reporter: philip hoy
> Priority: Minor
> Attachments: SOLR-4449.patch, SOLR-4449.patch, SOLR-4449.patch, patch-4449.txt, solr-back-request-lb-plugin.jar
>
>
> Add the ability to configure the built-in solr load balancer such that it submits a backup request to the next server in the list if the initial request takes too long. Employing such an algorithm could improve the latency of the 9xth percentile albeit at the expense of increasing overall load due to additional requests.
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