Unlike ExactStatsCache this implementation preserves term stats
across queries in a set of LRU caches, and based on surface features of a
query it determines the need to send additional RPC-s. As a result the
additional RPC-s are needed much less frequently.
Query terms and their stats are maintained in a set of maps. At the query
front-end there will be as many maps as there are shards, each maintaining
the respective shard statistics. At each shard server there is a single map
that is updated with the global statistics on every request.
Nested Class Summary
Nested classes/interfaces inherited from class org.apache.solr.search.stats.ExactStatsCache