I am in a confusion what could be the better design approach.
I am currenly connected to a legacy system which is a primary, now I need to migrate to oracle (secondary)...but don't want to shutdown my primary DB immedietly which will become secondary after the migration...for this what is the correct solution in terms of solution archiecture... Want to maintain both primary and secondary for some time.
I'd suggest to have all datasource (I assume legacy is kind of datasource) migration scripts ready and tested. Copy data over and connect both datasources to your system. Next try to keep updating (update, create, delete operations) both datasources, but proceed all read operations from original datasource. After a while check consistency of data in the second datasource and if it looks OK try to switch to it (but keep updating the legacy to make sure that you can always come back in case of any probs).