Another restriction on LOB columns is that the CD tables only contain an "update indicator", i.e. a flag saying whether the LOB was changed ('U') or not (NULL). The Apply process will, upon discovering the 'U', issue a query against the actual source table to grab the real LOB value and send it to the target database. The obvious issue with that is that CD table entries are not synchronized with the source table, i.e. Apply may read a newer LOB value. Depending on your scenario, this may result in seeing no visible change - for example, if you change LOB value A to B and then back again. The advantage of this approach is that the LOB values will not be copied to CD tables, doubling the amount of space required.