Ecto.Adapters.DynamoDB.Query.get_best_index-exclamation-mark

You're seeing just the function get_best_index-exclamation-mark, go back to Ecto.Adapters.DynamoDB.Query module for more information.
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get_best_index!(repo, tablename, search, opts \\ [])

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Same as get_best_index, but refers to a scan option on failure