title: Mysterious hash collision issue in DynamoDB
body: <p>I am pretty new in DynamoDB. I am currently investigating an issue in DynamoDB. Once a transaction file was validated as a normal transaction in a lambda, dynamoDB has found it duplicated transaction. It turned out it was not a duplicated transaction and it had to be normally processed with other transactions. But it was not the successful case weirdly. I am suspecting that there was collision when it compared hashes(partition key) and somehow it understood the key was not unique enough. It is definitely unique one along with sort key. If it is a duplicated matter, it throws ConditionalCheckFailedException in the current situation and it won't be recorded further once it's filtered in db. I would like to have a better understanding on how DynamoDB can have the issue and what could be the good solutions to prevent the same incident. It never had this issue before. If you have any idea, I would love to hear you!</p>