Resolve slow Solr indexing after Fusion upgrade due to LRUCache deprecation

Issue

After upgrading Fusion and Solr, Solr index datasources may process documents at a significantly reduced rate compared to previous versions. This can occur even when CPU and memory usage remain below specified limits, and all other configurations appear unchanged.

Diagnosis

• Indexing jobs process documents at a slower rate after upgrading Fusion (and Solr), with throughput reduced by approximately half compared to the previous version.

• The job configuration, CPU, and memory allocations remain unchanged from the previous deployment.

• No errors are observed in resource utilization monitoring.

• Solr logs display errors similar to:

Error instantiating cache => org.apache.solr.common.SolrException: Error loading class 'solr.LRUCache'

Environment

• Fusion 5.9.x (Self-Hosted on Kubernetes)

• Solr 9.1.x (as included with Fusion 5.9.x)

• Amazon EKS or other supported Kubernetes platforms

Note: The specific Solr and Fusion versions in use must be confirmed, but this guidance applies to all recent Fusion 5.x releases using Solr 9.x.

Cause

Solr’s LRUCache implementation has been deprecated and removed in recent versions. If the cache type in solrconfig.xml remains set to LRUCache after upgrading, Solr cannot instantiate the cache, which can negatively impact performance for indexing and query operations.

Resolution

Update your Solr configuration to use CaffeineCache instead of the deprecated LRUCache.

Update solrconfig.xml

1. Open the solrconfig.xml file for the affected Solr collections.

2. Locate any cache configuration entries referencing LRUCache. For example:

    

   <cache name="filterCache"
          class="solr.LRUCache"
          size="512"
          initialSize="512"
          autowarmCount="0"/>
   

3. Change the class attribute from solr.LRUCache to solr.CaffeineCache:

    

   <cache name="filterCache"
          class="solr.CaffeineCache"
          size="512"
          initialSize="512"
          autowarmCount="0"/>
   

4. Repeat this update for all cache entries referencing LRUCache (such as queryResultCache, documentCache, etc.).

5. Save your changes and apply the updated solrconfig.xml to the relevant Solr cores or collections.

6. Restart the Solr pods as necessary for the new configuration to take effect.

Note: For further details on CaffeineCache, refer to the Solr documentation.