CODEWITHSUNDEEP
ruby-on-railsrubyamazon-web-servicesamazon-sqs
rubyist
rubyist

Reputation: 3132

how to retrieve nth item in a queue with amazon sqs and ruby

Iam sending messages to the queue and using amazon sqs queuing system in a rails application. But since the queue follows FIFO process, it will get the next items in the same fashion. Suppose if I have 100 items in a queue, how can I retrieve the 35th item from the queue and process it. As far as I know, there is no such method that amazon sqs provides for doing it. So is there any other method/workaround where I can achieve the this functionality.

Upvotes: 0

Views: 324

Answers (2)

Nikhil
Nikhil

Reputation: 3152

SQS is designed to guarantee at-least-once delivery and does not take into account the order of messages. So the simple answer to your question on whether you can do that, is no.

A work around would depend on your use-case:

  1. To split work among different processes handling queue messages and making sure they don't both process the same item - Different queues is one approach, or prefixing every message with an identifier denoting which process is supposed to work on it. For example, if I have 4 daemons's running, I could prefix every message in the queue with the ID of the process which should work on it - 1,2,3 or 4. Every process would only process messages with the number corresponding to it's ID.

  2. Order of arrival is critical - In this case, you're better off not using SQS because it wasn't to be used this way. CloudAMQP is a cloud based service that is based off RabbitMQ which is a true FIFO queue and would suit this case better than SQS.

Upvotes: 0

E.J. Brennan
E.J. Brennan

Reputation: 46841

There is no method to do that; SQS does not guarantee order of items in the queue due to its geographically redundant nature; it can't even guarantee FIFO. If you absolutely must process things in order, and need the ability to 'look ahead' in the queue, SQS may not be your best choice. Perhaps a custom made queue in something like DynamoDB may be work better.

Upvotes: 1

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