14.1 Migration Considerations

This section discusses various factors to be considered while migrating LOB data types or storage.

Space requirements

Most migration techniques copy the contents of the table into a new space, and free the old space at the end of the operation. This temporarily doubles the space requirements. If space is limited, then you can perform the BasicFile to SecureFile migration one partition at a time.

Preventing Generation of REDO Data When Migrating

Migrating LONG datatype or BasicFiles LOB columns to SecureFile generates redo data, which can slow down the performance during the migration.

Redo changes for a column being converted to SecureFiles LOB are logged only if the storage characteristics of the LOB column indicate LOGGING. The logging setting (LOGGING or NOLOGGING) for the LOB column is inherited from the tablespace in which the LOB is created.

You can prevent redo space generation during migration to SecureFiles LOB by following the following steps:

1. Specify the NOLOGGING storage parameter for any new SecureFiles LOB columns.
2. Turn LOGGING on when the migration is complete.
3. Make a backup of the tablespaces containing the table and the LOB column.