I've successfully performed an online upgrade from TT6.0 to TT11.2 using the characterset TIMESTEN8. Once I have both nodes running TT11.2 with characterset=TimesTen8, I attempt an online upgrade (-noCharSetConversion option) to a different characterset, i.e. US7ASCII. After performing the ttMigrate out/in steps, the number of replication connections does not match the number before the migrate. The mate node is still set as TIMESTEN8
07:43:02.08 Err : REP: 6029: SYSTEMCONFIGURATION:receiver.c(14820): TT17017: The database character set differs from its peer
Can the characterset be changed during an online upgrade? If not, is it possible to keep characterset=TIMESTEN8 settting? What's the best characterset that most closely matches the current TIMESTEN8?
In order to replicate with each other both TimesTen databases must be using the same character set. Hence it is not possible to perform an online upgrade that includes changing the database character set. To do that you will need to take some downtime.
TIMESTEN8 character set is a binary 8-bit clean character set. It is not really a 'character set' as such but rather it maintains the behaviour of older, non-NLS capable, TimesTen releases. It is not possible to say therefore which of the many Oracle compliant character sets might be best for you; that depends on the actual data that you have stored and how you intend to use the data. None of the NLS character sets provide exactly the same behaviour as TIMESTEN8.