The Designer lets you convert data by passing it from port to port. Sometimes a conversion causes a numeric overflow (numeric data) or truncation (on character columns). For example, passing data from a Decimal (28, 2) to a Decimal (19, 2) port causes a numeric overflow. Likewise, if you pass data from a String(28) port to a String(10) port, the Integration Service truncates the strings to 10 characters. When a conversion causes an overflow, the Integration Service, by default, skips the row. The Integration Service does not write the data to the reject file. For strings, the Integration Service truncates the string and passes it to the next transformation.
The Designer provides an option to let you include all truncated and overflow data between the last transformation and target in the session reject file. If you select Reject Truncated/Overflow Rows, the Integration Service sends all truncated rows and any overflow rows to the session reject file or to the row error logs, depending on how you configure the session.