At initialization, the DTM allocates the buffer memory that the session will use at run time. You can configure the Integration Service to automatically allocate the buffer memory size or you can set the memory buffer and block size.
By default, the PowerCenter Integration Service automatically calculates the buffer memory required for a session based on the transformation requirements and the sources and targets in the mapping. The calculation is not based on the amount of memory on the host machine or on how much of that memory is available. In some cases, the PowerCenter Integration Service might allocate only a small portion of the available memory to the session.
If the buffer memory automatically calculated by the PowerCenter Integration Service does not appear to produce the memory footprint that you expect for a session, you can specify the size of the buffer memory and the size of the blocks that the PowerCenter Integration Service allocates to the session.