Any time an item is inserted/updated/removed from a DynamoDB table, a record in written to the stream and stored for up to 24 hours.
Streams allow to capture a time-ordered sequence of item level modifications
Depending on your use case you can define what data to put in the stream:
Keys only
New image
Old image
both old and new image ( meaning entire attributes before and after the modification)
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"arn:aws:dynamodb:{aws-region}:{aws-account-number}:table/{table-name}/stream/2019-11-07T20:49:20.459"