For the IOM driver,
the default fetch size is calculated dynamically unless the fetch
size is set manually with the setFetchSize method. The getFetchSize
method returns 0 to indicate the dynamic sizing. The calculation is
performed at run time by determining the width of a row in the result
set, and then determining how many rows can be stored in a 16-kilobyte
buffer.
This value works well
in most cases, and also takes into consideration data sources that
have either narrow rows (few columns or short CHAR columns) or wide
rows (many columns or long CHAR columns). For data sources with narrow
rows, the result set can hold many rows to improve performance. For
data sources with wide rows, the result set holds fewer rows so that
memory consumption does not reduce performance. Use the setFetchSize
method to override this behavior.
The
SAS/SHARE driver
uses a default fetch size of 10 rows. This value can be changed with
the setFetchSize method, but this driver does not perform a dynamic
calculation for the optimal fetch size.