Short and Long Polling¶

Reference: https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-short-and-long-polling.html

什么是 Short Polling¶

SQS 后台是分布式的, 一个队列的许多消息是分布在多台机器上的. Short Polling 是指每次消费数据时, 根据权重从这些机器上随机采样, 并汇总返回数据. 但是这是完全可能采样到的机器上没有消息, 导致返回 Empty Response. 或是其他机器上有消息, 但是被采样的机器没有, 这又叫 False Empty Response.

什么是 Long Polling¶

长轮询是指客户端发起消费请求时, 如果队列中没有消息, 队列不会立刻返回, 而是 Hold 住一段时间直到返回数据. 这样能够减少 Empty Response 的概率, 从而节约开支, 提高效率.

Differences Between Long and Short Polling¶

Short polling occurs when the WaitTimeSeconds parameter of a ReceiveMessage request is set to 0 in one of two ways:

The ReceiveMessage call sets WaitTimeSeconds to 0.
The ReceiveMessage call doesn’t set WaitTimeSeconds, but the queue attribute ReceiveMessageWaitTimeSeconds is set to 0.