[syslog-ng] Flow-control

Could you please explain the following statement:

If the control window is full, syslog-ng stops reading messages from the source until some messages are successfully sent to the destination.

What does that mean - "stops reading messages from the source"? My applications is still sending messages to this souce so where will all the logs at that moment? Where will it start reading the source? From the same point it stopped or not? -- Best regards, Koldaev Anton