Updating index statistics is an I/O expensive operation.

Index statistics are calculated from pages buffered in the buffer pool for tables with InnoDB storage engine.

Setting innodb_stats_auto_recalc=ON causes statistics to be updated automatically when a new index is created.

Execution plans based on transient index statistics improve precision when

innodb_stats_persistent_sample_pages is increased.

Increasing innodb_stats_persistent_sample_pages determines higher pages scanning speed, at the cost of increased memory usage.

Tables are scanned and index statistics recalculated when an instance is restarted.