Sizing a LOB or XML Subtable
One LOB or XML subtable is required for each column in a base table defined with a BLOB, CLOB, or XML data type. Depending on the size of each LOB or XML string, the cardinality of the subtable can exceed the cardinality of the base table. Estimate the size of your LOB and XML subtables using the equations provided in “LOB and XML Subtable Sizing Equation” on page 862.
Because LOBs and XML strings are variable length entities, there are no alignment issues for aligned row format systems.