The Auto Query Plan Improvement feature collects and stores query plan statistics in a statistics cache when a query is executed in MySQL HeatWave. When a new query shares query execution plan nodes with previously executed queries, the statistics collected from previously executed queries are used instead of estimated statistics, which improves query execution plans, cost estimations, execution times, and memory efficiency.

Each entry in the cache corresponds to a query execution plan node. A query execution plan may have nodes for table scans, JOIN, GROUP BY and other operations.

The statistics cache is an LRU structure. When cache capacity is reached, the least recently used entries are evicted from the cache as new entries are added. The number of entries permitted in the statistics cache is 65536, which is enough to store statistics for 4000 to 5000 unique queries of medium complexity. The maximum number of statistics cache entries is defined by the MySQL-managed rapid_stats_cache_max_entries setting.