Migration and Changing are two distinctly different types of problems that can exist when a row is too large to fit into a single data block.

Row Changing:: Row changing occurs when a row is too large to fit into a single empty data block. When this occurs, Oracle will spread the row across as many blocks as are needed. Changing the row from from one block to the next.

Row Migration:: Row migration occurs when a row is updated and it will not fit back into the original block. When this happens, the Oracle server attempts to find another block that the entire row can be moved to. If it does find a block, the entire row is moved to the new block. The row piece(head ROWID) remains in the original block, with original ROWID and points to the migrated rowin the new block.