Commands | AMQP QoS

AMQP allows to set a QoS level to limit the number of messages the server sends to the client before wait to get the acknowledgment of the messages.

 

Set QoS

The method SetQoS is used to limit the number messages the server sends to the AMQP client.

The method has the following arguments:

 

• ChannelName: it's the name of the channel (must be open before call this method).
• PrefetchSize: it's the windows size in bytes, the server doesn't send messages to the client if the total size of all currently unacknowledged messages already sent plus the next message to be sent it's greater than PrefetchSize argument. If the value is zero, means no limit.
• PrefetchCount: is the maximum number of unacknowledged messages already sent and not acknowledged, if the number is greater, the server stops sending messages to the client.
• Global: if true the QoS applies to all existing and new consumers of the connection. If false, the QoS applies to all existing and new consumers of the channel.

 

The response from the server is received OnAMQPBasicQoS event.

AMQP.SetQoS('channel_name', 1024000, 100, false);
 
procedure OnAMQPBasicQoS(Sender: TObject; const aChannel: string; 
  const aQoS: TsgcAMQPFramePayload_Method_BasicQoS);
begin
  DoLog('#AMQP_basic_qos: ' + aChannel + ' ' + IntToStr(aQoS.PrefetchSize) + ' '
    + IntToStr(aQoS.PrefetchCount) + ' ' + BoolToStr(aQoS.Global));
end;

 

A Synchronous call can be done just calling the method SetQoSEx, this method returns true if the request has been processed, otherwise the result will be false.