like i said, if you believe that...
mysql places the rows onto the disk wherever there happens to be space available
without getting into a lot of detail, this is ~not~ always going to be "fifo"
furthermore, if you do not include an ORDER BY clause in your SELECT statement, mysql can return the rows in whatever sequence it finds convenient
can you be sure that rows that happen to be in a buffer will be re-retrieved in fifo sequence? or could you not imagine that mysql will return the rows in the buffer first, and then go and retrieve the others off the disk
DO NOT rely on anything other than ORDER BY to retrieve rows in a given sequence
if you want fifo, use a datetime column