By default, queues use short polling.

▪ Short polling, the ReceiveMessage request queries

only a subset of the servers to find messages that are

available to include in the response.

▪ Long polling, the ReceiveMessage request queries all

of the servers for messages. Amazon SQS sends a

response after it collects at least one available

message.

▪ Consume messages using short polling, Amazon SQS

samples a subset of its servers and returns messages

from only those servers.

▪ When the wait time for the ReceiveMessage API

action is greater than 0, long polling is in effect. Long

polling helps reduce the cost of using Amazon SQS

by eliminating the number of empty responses.

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