Simple Queue Service (SQS)

SQS standard (offers as the default queue type)

• nearly-unlimited number of transactions per second

• message is delivered at least once (more than one copy of a message might be delivered out of order)

  

FIFO queue

• message is delivered once (remain until a consumer processes and deletes it)

• 300 transactions per second

  

Tips

• SQS is pull based, not pushed based
• messages are 256KB in size
• messages can be kept in the queue from 1 minute to 14 days, the default retention period is 4 days
• VisibilityTimeout: the amount of time that the message is invisible in the SQS queue after a reader picks up that message. Provided the job is processed before the visibility time out expires, the message will then be deleted from the queue. If the job is not processed within that time, the message will become visible again and another reader will process it. This could result in the same message begin deliverd twice
  • Visibility timeout maximum is 12 hours
• DelaySeconds: when a new message is added to the SQS queue, it will be hidden from consumer instances for a fixed period
• SQS long polling is a way to retrieve messages from your Amazon SQS queues. While the regular short polling returns messages immediately (even if the message queue being polled is empty), long polling doesn't return a response until a message arrives in the message queue, or the long poll times out ⇒ save money
  • WaitTimeSeconds + ReceiveMessageWaitTimeSeconds: when the consumer instance polls for new work, the SQS service will allow it to wait a certain time for one or more message to be available before closing the connection (if is 0 ⇒ short polling)

Simple Workflow (SWF)

• not recommended in following situation
  • if need external signals to intervene in the process
  • if need child processes that return values to parent processes

SQS vs SWF

SWF

• retention period 1 year

• task-oriented API

• task is assigned only once and is never duplicated

• keep track all the task and event

SQS

• 14 days
• message-oriented API
• need to handle duplicated messages and ensure that a message is processed only once
• need to implement your own application-level tracking, especially if you use multiple queues

SWF Actors

• workflow starter - initiate workflow