This KB provides information about some of the key concepts when migrating data from one instance to the other. As the name suggests, data migration is a very sensitive topic and one of the most critical factors for its successful completion is to follow the correct sequence of steps while importing data into the target. Though this KB does not intend to provide an exhaustive narrative of each and every step involved, it highlights the major contributing aspect for a successful migration.
1) Identify the source and target instances carefully.
2) Identify the mechanism for how the data is going to be moved over (XML, import set, etc).
3) Once the records have been imported into the target instance the following should be imported in the given order.
i) Import all audit data for all records which have been imported into the target instance
ii) Import all journal entry data from sys_journal for each respective record imported to the target instance.
The consequences of importing data out of order can result in major inconsistencies for the imported raw data as the activity formatter may display incorrect information. Additionally the data entries in the target may not match up with those in the source and the impact may be significant. The reason for this behavior is due to records being viewed before audit data is present. When a record is viewed for the first time a history set is generated for that particular record with data that is available from sys_audit. If the audit data for the record is not present when the record is viewed for the first time it will generate an incorrect history set.
It is imperative to adhere to the steps above which can avoid unnecessary hassles and delays. If for some reason, an incorrect sequence is followed for the data import then the fix would be to delete the history set. When the record is viewed again, it will now rebuild the correct history set provided the audit data is present.