Flow-control and multiple destinations

Using flow-control on a source has an important side-effect if the messages of the source are sent to multiple destinations. If flow-control is in use and one of the destinations cannot accept the messages, the other destinations do not receive any messages either, because syslog-ng OSE stops reading the source. For example, if messages from a source are sent to a remote server and also stored locally in a file, and the network connection to the server becomes unavailable, neither the remote server nor the local file will receive any messages.

NOTE: Creating separate log paths for the destinations that use the same flow-controlled source does not avoid the problem.

If you use flow-control and reliable disk-based buffering together with multiple destinations, the flow-control starts slowing down the source only when:

• one destination is down, and

• the number of messages stored in the disk buffer of the destination reaches (disk-buf-size() minus mem-buf-size()).