Can a SQS consumer receives duplicated message during visibility timeout of message?

Question

I am building an application using SQS standard queue, which will trigger Lambda function when a new message is available in the queue. I am aware that my Lambda function might receive a duplicated message which it has processed before:

On rare occasions, one of the servers that stores a copy of a message might be unavailable when you receive or delete a message. If this occurs, the copy of the message isn't deleted on that unavailable server, and you might get that message copy again when you receive messages.

Based on my understanding, the Lambda service will launch multiple instances of my Lambda function, and that different instances of my Lambda function might process the same message. But according to the developer guide,

Immediately after a message is received, it remains in the queue. To prevent other consumers from processing the message again, Amazon SQS sets a visibility timeout, a period of time during which Amazon SQS prevents other consumers from receiving and processing the message.

I would like to know whether one instance of my Lambda function might received a duplicated message while another instance of my Lambda function is still processing the message. That is, I want to know whether it is possible for one Lambda instance to receive a message while the message is in visibility timeout.

Thank you in advance.

Answer 1

After reading these docs

No if its still processing the message then it can't but if the processing is failed then it might. In my view it depends on the number of messages and batch.

Lambda reads messages in batches and invokes your function once for each batch. When your function successfully processes a batch, Lambda deletes its messages from the queue.

1. This establishes the fact the concurrency of lambda depends on batch.

When Lambda reads a batch, the messages stay in the queue but are hidden for the length of the queue's visibility timeout. If your function successfully processes the batch, Lambda deletes the messages from the queue. By default, if your function encounters an error while processing a batch, all messages in that batch become visible in the queue again

2. This established the fact the all messages in the batch should be processed otherwise they will be visible in the queue.

For standard queues, Lambda uses long polling to poll a queue until it becomes active. When messages are available, Lambda reads up to five batches and sends them to your function. If messages are still available, Lambda increases the number of processes that are reading batches by up to 60 more instances per minute. The maximum number of batches that an event source mapping can process simultaneously is 1,000.

3. This establishes that a single lambda can read up to 5 batches.

Combining all the 3.

If it is upto 5 batch a single lambda can process 5 batches, if it is more than 5 batch multiple lambda will be invoked and in this time if the previous lambda couldn't process the message and it reappears in the queue and the new invoked lambda will be able to read the previous messages which was not be ables to processed.

This blog also explains the same better than docs https://data.solita.fi/lessons-learned-from-combining-sqs-and-lambda-in-a-data-project/