MySQL

5.7以前はauto-incrementカウンターはメモリ上にのみ保持される

If you specify an AUTO_INCREMENT column for an InnoDB table, the in-memory table object contains a special counter called the auto-increment counter that is used when assigning new values for the column.

In MySQL 5.7 and earlier, the auto-increment counter is stored in main memory, not on disk. To initialize an auto-increment counter after a server restart, InnoDB would execute the equivalent of the following statement on the first insert into a table containing an AUTO_INCREMENT column.

In MySQL 8.0, this behavior is changed. The current maximum auto-increment counter value is written to the redo log each time it changes and saved to the data dictionary on each checkpoint. These changes make the current maximum auto-increment counter value persistent across server restarts.