When a session runs without high precision, the Integration Service converts decimal values to doubles. The transformation Decimal datatype supports precision of up to 28 digits, while the Double datatype supports precision of up to 15 digits. Therefore, precision loss occurs if the decimal value has a precision greater than 15 digits.
For example, you have a mapping with Decimal (20,0) that passes the number 40012030304957666903. If the session does not run with high precision, the Integration Service converts the decimal value to double and passes 4.00120303049577 x 10
To ensure precision of up to 28 digits, use the Decimal datatype and enable high precision in the session properties. When you run a session with high precision, the Integration Service processes decimal values as Decimal. Precision loss does not occur in a calculation unless the result produces a value with precision greater than 28 digits. In this case, the Integration Service stores the result as a double.