Sitecore generating Overlapping onDeckSearchers=x warnings in Solr logs

I’ve recently had an issue where every 10 minuets or so a entry would appear in the Solr logs. This was only an issue for the analytics core. After reading various articles and try different Solr configurations I failed to resolve the problem.

However after a chat with Sitecore Support the issue was resolved by a quick change to our Sitecore environment. Our production environment consists of four separate Sitecore instances, two delivery, one authoring and one processing server. By default Sitecore uses a Timed Index Refresh Strategy to update Solr’s analytics core. By having four environments pointing to the same Solr instance, the analytics core was being updated four times simultaneously.

When a processing server is being used only that should update the analytics core. In an environment without a processing server it would the possibility of authoring server.

To resolve the issue the processing server was left with the default Timed Index Refresh Strategy. Automatic updating of the analytics was disabled on the remaining three environments by changing the strategy to manual.

The strategies are set in the Sitecore.ContentSearch.Solr.Index.Analytics.config file. The default is:

<strategies hint="list:AddStrategy">
   <timed type="Sitecore.ContentSearch.Maintenance.Strategies.TimedIndexRefreshStrategy, Sitecore.ContentSearch">
      <param desc="interval">00:01:00</param>

To use a manual strategy remove the above from the config file and add:

<strategies hint="list:AddStrategy">
   <strategy ref="contentSearch/indexConfigurations/indexUpdateStrategies/manual" />

Rather than updating the config file a better solution would be creating a patch file. This way if the config file is replaced during an upgrade the config change will still be applied.