Advanced MySQL 8

Control the types of data change operations

When operations such as INSERT, UPDATE, and DELETE are run on a table, the values of the indexed columns are often in unsorted order, and this will require input/output; updating the secondary indexes included will adversely affect performance.

However, InnoDB caches (in memory) the changes made to secondary index entries when the corresponding page is not in the memory pool, thus avoiding expensive input/output operations by not immediately reading the page from the disk. The stored changes are in this case merged when the page is loaded into this memory pool and the updated page is then flushed to disk.