QoS策略

• History

  • Keep last: only store up to N samples, configurable via the queue depth option.

  • Keep all: store all samples, subject to the configured resource limits of the underlying middleware.

• Depth

  • Queue size: only honored if the “history” policy was set to “keep last”.

• Reliability

  • Best effort: attempt to deliver samples, but may lose them if the network is not robust.

  • Reliable: guarantee that samples are delivered, may retry multiple times.

• Durability

  • Transient local: the publisher becomes responsible for persisting samples for “late-joining” subscriptions.

  • Volatile: no attempt is made to persist samples.

• Deadline

  • Duration: the expected maximum amount of time between subsequent messages being published to a topic

• Lifespan

  • Duration: the maximum amount of time between the publishing and the reception of a message without the message being considered stale or expired (expired messages are silently dropped and are effectively never received).

• Liveliness

  • Automatic: the system will consider all of the node’s publishers to be alive for another “lease duration” when any one of its publishers has published a message.

  • Manual by topic: the system will consider the publisher to be alive for another “lease duration” if it manually asserts that it is still alive (via a call to the publisher API).

• Lease Duration

  • Duration: the maximum period of time a publisher has to indicate that it is alive before the system considers it to have lost liveliness (losing liveliness could be an indication of a failure).

The following tables show the compatibility of the different policy settings and the result:

Compatibility of reliability QoS policies:

Compatibility of durability QoS policies:

Compatibility of deadline QoS policies:

Assume x and y are arbitrary valid duration values.

Compatibility of liveliness QoS policies:

Compatibility of lease duration QoS policies:

Assume x and y are arbitrary valid duration values.

 
   为了建立连接，所有影响兼容性的策略都必须是兼容的。例如，即使请求和提供的QoS配置文件对具有兼容的可靠性QoS策略，但它们具有不兼容的持久性QoS策略，仍然不会建立连接。当没有建立连接时，将不会在发布者和订阅之间传递消息。