> InnoDB’s Three Guarantees

Rows store all columns together

Not guaranteed. The DYNAMIC (default) and COMPRESSED row formats [0] can shift larger values of variable-length columns in off-page records. In the example given, this wouldn’t occur, but it isn’t a guarantee per se. This is roughly equivalent to Postgres’ TOAST, though Postgres’ default threshold for TOAST is 1/4 of a page (2 KiB with its default 8 KiB page size), whereas InnoDB is 1/2 of a page (8 KiB with its default 16 KiB page size).

0: https://dev.mysql.com/doc/refman/9.7/en/innodb-row-format.ht...