We're in the middle of an upgrade from mysql 5.1 to mysql 5.5. Our only remaining holdout is the master, at 5.1, while all the slaves are at 5.5.
However, we have a stats process that runs on an admin slave, which rsyncs the myisam files to the master, who mount it in a stats DB, then imports those stats into the main production db.
All the tables use the default row_format for myisam, which is static. We're only using simple column types: int, varchar, enum, datetime.
We've already run this process, and it didn't fall down, which is encouraging. But I'm concerned with errors that didn't make it into the log.
So the question is: what are the complications of this process? The MyISAM file is created by a 5.5 instance, then moved to a 5.1 instance.
What's going to go wrong?
(This is a duplicate post to https://stackoverflow.com/questions/9415715/can-mysql-5-1-read-a-mysql-5-5-myisam-file, where there was no detailed answer available.)