(PECL solr >= 2.2.0)
SolrQuery::setGroupCachePercent — Enables caching for result grouping
Setting this parameter to a number greater than 0 enables caching for result grouping. Result Grouping executes two searches; this option caches the second search. The server default value is 0. Testing has shown that group caching only improves search time with Boolean, wildcard, and fuzzy queries. For simple queries like term or "match all" queries, group caching degrades performance. group.cache.percent parameter
percent
Emits SolrIllegalArgumentException in case of an invalid parameter was passed.