> We also used the maatkit tools to verify replication integrity.  I hooked up a 5.0.84 slave to a 4.1 master, replayed 24 hours worth of logs, and ran mk-table

> We also used the maatkit tools to verify replication integrity.  I hooked up a 5.0.84 slave to a 4.1 master, replayed 24 hours worth of logs, and ran mk-table-checksum/mk-table-sync on the whole thing as a consistency check.  Unfortunately, the consistency check showed that the slave and master had slightly inconsistent data after only a few hours.  Doubly-unfortunately, these inconsistencies were not unique to the test scenario; we also see them in replication between 4.1->4.1, 4.1->5.0, and 5.0->5.0.  This is probably a topic for another blog post; for now, suffice it to say, I verified that the upgrade was not going to introduce any new bugs, and left it alone.a1 Emph. mine.