PostgreSQL vs DynamoDB

When I'd use DDB:

• if key value access is enough
• I need heavy write (more than 10k writes per second)
• automatic and managed sharding

What you're giving up with postgres:

• relations and joins: in ddb, you have to manage constraints yourself or duplicate documents
• ad-hoc querying: harder to find specific data or debug without doing sequential scans
  • you lose ability to do aggregations like group by or avg
• transactions
• strong consistency
• cost predictability (some ddb queries can be expensive as you pay per query)