Flow Control

Flow control is the process of managing the rate of data transmission between two nodes to prevent a fast sender from overwhelming a slow receiver.

In the messaging platform flow control is possible both between the messaging platform and the message handlers, and between the nodes in the messaging platform cluster.

Messaging Platform - Messaging Handler:

The client (i.e. the Axon Application) needs to set the following properties to configure flow control:

• axon.axonserver.initial-nr-of-permits [1000] - number of messages that the server can initially send to client.

• axon.axonserver.nr-of-new-permits [500] - additional number of messages that the server can send to client.

• axon.axonserver.new-permits-threshold [500] - when client reaches this threshold in remaining messages, it sends a request with additional number of messages to receive.

Axon Server Nodes:

Set the following properties to control 'list aggregate events' prefetch rate, per aggregate and per segment:

• axoniq.axonserver.event.aggregate.prefetch [5] - Ensures that backpressure signals from clients are split into batches. The initial request amount is {prefetch}*5, and subsequent (or replenishing) request amount is {prefetch}

• axoniq.axonserver.event.events-per-segment-prefetch [10] - the maximum prefetched events from each opened event segment (max two opened segments in parallel)

Set the following properties to set flow control on the synchronization between nodes in an Axon Server cluster:

• axoniq.axonserver.commandFlowControl.initial-nr-of-permits [10000] - number of messages that the master can initially send to replica.

• axoniq.axonserver.commandFlowControl.nr-of-new-permits [5000] - additional number of messages that the master can send to replica.

• axoniq.axonserver.commandFlowControl.new-permits-threshold [5000] - when replica reaches this threshold in remaining messages, it sends a request with additional number of messages to receive.

• axoniq.axonserver.queryFlowControl.initial-nr-of-permits [10000] - number of messages that the master can initially send to replica.

• axoniq.axonserver.queryFlowControl.nr-of-new-permits [5000] - additional number of messages that the master can send to replica.

• axoniq.axonserver.queryFlowControl.new-permits-threshold [5000] - when replica reaches this threshold in remaining messages, it sends a request with additional number of messages to receive.