Simple Queue Service (SQS) Cheat Sheet

• Serverless message queue
• 2 Types
  • Standard
  • FIFO

Visibility Timeout

• When a message is received, it is made invisible to subsequent ReceiveMessage calls for a duration called “visibility timeout”
• Consumer should delete processed messages, or the message will reappear after the timeout
• Can be set to 0 seconds to 12 hours, default 30 seconds
• Messages will be discarded after a retention period (can be set to 60 seconds to 14 days, default 4 days)

Polling

• Short polling
  • SQS samples queue nodes and returns messages immediately
  • May not return all messages as this is sample-based
  • Cloud return empty results

• Long polling
  • SQS waits up to 20 seconds to in attempt to get at least 1 message (less empty responses)
  • SQS query all queue nodes so no message in queue is missed
  • Note: long polling API is still synchronous so make sure your application can keep connection open during timeout
• Short vs. long 🎓
  • Return immediately vs. return after a given timeout or a message is received
  • Sample some nodes vs. query all nodes
  • More likely to return empty results vs. only return empty result after timeout and no messages received
  • Technically they both use ReceiveMessage API, only the WaitTimeSeconds parameter in long polling is set to value larger than 1
  • Because of long polling reduces number of requests, the cost of using long polling is lower than short polling
    • SQS is billed by number of requests so it does not matter a request is short or long polling
• Use cases
  • Use short polling when immediate return of result is needed
  • Otherwise, use long polling