Estimate. IBM Informix ODBC Driver makes a worst-case estimate of the storage space needed to return the data.
Exact. IBM Informix ODBC Driver writes the code-set-converted data to disk until all the data is converted. Because this option can degrade performance, it is recommended that you do not use this option unless your application does not work with Estimate.
When you use a multibyte code set (in which characters vary in length from 1 to 4 bytes) for either the database or client locale, the length of a character string or simple large object (TEXT) in the database locale does not indicate the length of the string after it is converted to the client locale.