Grow queryResultCache (size=512, 56% hit rate, 317K evictions)

[gaurav]

Summary

Production /status?full=true shows the Solr queryResultCache is undersized for the workload. filterCache is sized correctly (99.8 % hit ratio, no evictions), so the same workload is mostly variation in the q clause that queryResultCache is supposed to absorb.

Evidence

Cache	Hit ratio	Size	Lookups	Hits	Evictions
filterCache	0.998	74	43,030	42,956	0
queryResultCache	0.565	512	749,258	423,353	317,758

A 56 % hit rate on a cache that has evicted 317 K entries strongly suggests the working set is much larger than the configured 512 slots.

Suggested action

In solrconfig.xml (managed in the Helm chart, not this repo), bump queryResultCache to:

<queryResultCache class="solr.search.CaffeineCache"
                  size="4096"
                  initialSize="2048"
                  maxRamMB="512"
                  autowarmCount="0"/>

Using maxRamMB rather than (or in addition to) size bounds the cache by memory rather than entry count and is generally more robust.

How to verify after deploy

Hit /status?full=true after the change and a soak period:

• solr.cache.queryResultCache.size reflects the new ceiling
• solr.cache.queryResultCache.hitratio rises (target: > 0.85)
• solr.cache.queryResultCache.evictions rate per hour drops sharply