Hi,
 
Sparse, or serialized fields do not live as a column in the database table. Instead, their values are stored in JSON arrays in a separate field. As a result, these fields cannot be searched or sorted by. If such a sparse field is created as 'manual', this module can unserialize the field.
 
fields.serialized: Serialized field is used to store data in a field in a json dump

fields.sparse: Sparse field uses a serialized field to store a field in the json dump instead of a normal database column.

Regards