As mentioned in MDL-58931 Amazon Aurora MYSQL does not support row format of COMPRESSED, and instead falls back to COMPACT. Upgrades to 4.1 from 3.9 on Aurora MYSQL fail due to the error Index column size too large. The maximum column size is 767 bytes caused by the (silently) failed attempt to use COMPRESSED row format.

A fix would be to modify the is_compressed_row_format_supported function to return false if $CFG->dbtype = 'auroramysql'?