Description: The size of the initial window, this value is used during flow control. If the max-connections() option is set, the log-iw-size() will be divided by the number of connections, otherwise log-iw-size() is divided by 10 (the default value of the max-connections() option). The resulting number is the initial window size of each connection. For optimal performance when receiving messages from syslog-ng PE clients, make sure that the window size is larger than the flush-lines() option set in the destination of your clients.
If log-iw-size(1000) and max-connections(10), then each connection will have an initial window size of 100.