For instance, in Oracle, when a row is inserted or updated, the possibility exists that it will not fit in a single block or the originating block. When this happens, Oracle either chains or migrates the row. Performance is affected because more than one data block must be accessed to retrieve the information for that row. Row Chaining and Migration Row chaining occurs when a row is inserted or updated, and the row size is greater than the data block size, e.g., a 3K row cannot fit in a 2K data block. When this occurs, Oracle stores the data for the row in a chain of data blocks reserved for that segment.
Row chaining is a function of application design and database block size.
Row migration occurs when a row is updated and will not fit in the originating data block. Oracle migrates the row to a new block. Oracle must link the original row to the new block containing the migrated row. Both row chaining and row migration decrease performance and potentially waste database space. Row migration can be affected by appropriate storage parameters.