"false" is the default.
THIS IS A THIN ONLY PROPERTY. IT SHOULD NOT BE USED WITH ANY OTHER DRIVERS.
If set to "true", the performance when retrieving data in a 'SELECT' will be improved but the default behavior for handling LONG columns will be changed to fetch multiple rows (prefetch size). It means that enough memory will be allocated to read this data. So if you want to use this property, make sure that the LONG columns you are retrieving are not too big or you may run out of memory. This property can also be set as a java property :
java -Doracle.jdbc.useFetchSizeWithLongColumn=true myApplication