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Setup
- Solr version: 9.6.1
- Drupal Core version: 10.4.7
- Search API version: 8.x-1.38
- Search API Solr version: 4.3.10
- Configured Solr Connector: Solr connector plugin Standard
Issue
Using the downloaded configset from /admin/config/search/search-api/server/, we see exceptions in the solr logs:
2025-07-09 20:35:44.952 ERROR (coreLoadExecutor-11-thread-1) [c: s: r: x:maincore t:] o.a.s.s.CacheConfig Error instantiating cache => org.apache.solr.common.SolrException: Error loading class 'solr.search.LRUCache'
at org.apache.solr.core.SolrResourceLoader.findClass(SolrResourceLoader.java:551)
org.apache.solr.common.SolrException: Error loading class 'solr.search.LRUCache'
According to solr docs, the LRUCache was deprecated in 8.4 and removed in solr 9.0. (https://solr.apache.org/docs/8_4_0/solr-core/deprecated-list.html)
So that explains the exceptions. What it doesn't explain, though, is why search_api_solr is generating a config set that refers to a non-existent class. I see references like this in solrconfig_query.xml.
<!--
Field Value Cache
7.0.0
-->
<fieldValueCache class="solr.FastLRUCache" size="512" autowarmCount="128" showItems="32"/>
It seems like maybe the module needs to be updated to generate config that uses CaffeineCache instead, which is the new version supported in 9.
The standard connector is auto-detecting the correct solr version, so its not that.
Due to my PaaS provider, I have to use the standard connector, but maybe that connector is generating old version 8 configs? (grasping at straws now).
In any case, it looks like the configsets downloaded from this module at version 4.3.10 when connected to a solr 9.6 instance are not working, and are including references to Java classes that no longer exist in solr 9.