The gateway stores its data in the overflow area.
This area in the heap memory is retrieved by the gateway during initialization with malloc() default 10 MByte). The size of the overflow area is specified by the profile parameter gw/max_overflow_size.
The profile parameter gw/max_overflow_usage (specified as a percentage) specifies the usage of the overflow area as of which the gateway slows down the sender. If this value is exceeded, the sender is slowed down by SYNC calls. An SYNC ensures that control is returned to the sender only when the data has been retrieved by the receiver. You must, however, make sure that 5 CPIC requests can still be saved in the gateway, since the sender only executes CMSEND synchronously with every 5th request.
A specific number of requests can be temporarily stored per CPIC connection. The number of requests is determined by the profile parameter gw/req_stack_size. The default is 30. When the number of requests stored at one time exceeds the threshold value, the sender is slowed down by SYNC calls.
The threshold value is calculated according to the following formula:
max(stack_size-6 , stack_size*0,9),
whereby i stack_size is the value gw/req_stack_size.
By default the threshold value is the maximum of 24 (=30-6) and 27 (=30*0,9), therefore 27. The gateway starts to slow down the communication partner when 27 requests have accumulated.