Question

A developer writes a Lambda function that loads 200 records into a DynamoDB table using a series of BatchWriteItem calls (25 items each). During peak load, some responses return successfully but the function later discovers that not all records were actually written. Reviewing the SDK response reveals a non-empty UnprocessedItems map. What is the correct way to ensure all records are eventually persisted?

Accepted Answer

Resubmit only the items listed in the UnprocessedItems map in a subsequent BatchWriteItem call, using exponential backoff between retries.

Answer

Treat the non-empty UnprocessedItems map as a fatal error, abort the batch, and return a 500 to the caller.

Answer

Switch the table to on-demand capacity mode, which guarantees that BatchWriteItem never returns unprocessed items.

Answer

Re-send the entire original batch of 25 items again to guarantee the missing items are written.