How large is user's generated content in average? Have you considered S3 for your use case?
Storage in DDB can be quite pricey (when combining storage cost and and read capacity usage cost)
We are a messaging application, so every chat message is stored in DynamoDB in an ordered stream. We frequently fetch slices of a stream, so the granularity of storage is a single message.
S3 does not do well (cost wise) with billions of files. Provisioning 1000 Write IOPS on Dynamo costs around $100/month. That's 2.5B writes. On S3 that's going to be on the order of $10k. Similarly 1000 Read IOPS on Dynamo is ~$20/month vs 2.5B reads on s3 costing $1000. Storage is cheaper on S3 by about 10x, but per TB that comes out to $250 vs $25, which is hardly a dominating cost factor.
