Question

A developer configures an AWS Lambda function with a DynamoDB Streams event source mapping to process changes to an orders table. During load testing, the team notices that updates to the same order item are occasionally processed out of order, causing incorrect final states. The function is configured with a batch size of 100 and a parallelization factor of 10. What is the MOST likely cause and the correct fix?

Accepted Answer

The parallelization factor greater than 1 allows multiple concurrent batches per shard, breaking per-item ordering; set the parallelization factor to 1 to preserve ordering within a partition key.

Answer

The batch size of 100 is too large; reduce the batch size to 1 so each record is processed individually and ordering is guaranteed.

Answer

DynamoDB Streams does not guarantee any ordering; add a FIFO SQS queue between the stream and Lambda to enforce ordering.

Answer

The Lambda function's reserved concurrency is too low; increase reserved concurrency so records are not throttled and reordered.