If the machine has limited physical memory and the mapping in the session contains a large number of sources, targets, or partitions, you might need to decrease the buffer block size.
If you are manipulating unusually large rows of data, increase the buffer block size to improve performance. If you do not know the approximate size of the rows, determine the row size by completing the following steps.
To evaluate needed buffer block size:
In the Mapping Designer, open the mapping for the session.
Open the target instance.
Click the Ports tab.
Add the precision for all columns in the target.
If you have more than one target in the mapping, repeat steps 2 to 4 for each additional target to calculate the precision for each target.
Repeat steps 2 to 5 for each source definition in the mapping.
Choose the largest precision of all the source and target precisions for the total precision in the buffer block size calculation.
The total precision represents the total bytes needed to move the largest row of data. For example, if the total precision equals 33,000, then the Integration Service requires 33,000 bytes in the buffer block to move that row. If the buffer block size is only 64,000 bytes, the Integration Service cannot move more than one row at a time.
To set the buffer block size, open the session properties and click the Config Object tab. Edit the Default Buffer Block Size property in the Advanced settings.
As with DTM buffer memory allocation, increasing buffer block size should improve performance. If you do not see an increase, buffer block size is not a factor in session performance.