AWS Glue with Dynamo - Not getting DuplicateItemException when duplicate Primary keys are inserted

Question

#Part of Glue Job code - that is writing  dataframe into Dynamo   table

# Write df_dyn_target_1 into Dynamo database
    glueContext.**write_dynamic_frame_from_options**(
        frame=df_dyn_target_1,
        connection_type="dynamodb",
        connection_options={"dynamodb.output.tableName": "dy_lookup_table",
            "dynamodb.throughput.write.percent": "1.0"
        }
    )
I'm trying to write contents from dataframe (df_dyn_target_1) into "dy_lookup_table" table. As these records (primary keys = partition+sort) are already present in Dynamo table, I am expecting** "DuplicateItemException: Duplicate primary key exists in table"** and eventually a Glue Job failure. But it isn't working in that way and Job is successful. Do I need to pass any parameters in connection_options={} to solve the issue. 
Pleas suggest

Accepted Answer

You will not get a `DuplicateItemException` when you write an item which already exists, instead DynamoDB will just overwrite the existing item as this is how DynamoDB works.

Where you could receive a `DuplicateItemException` is when Glue creates a batch of 25 items to do its `BatchWriteItem` (which happens under the hood) and in that batch of 25, 2 or more items have the same key.

Unfortunately with Glue you cannot do a conditional write, as it uses `BatchWriteItem` and its not supported.

AWS Glue with Dynamo - Not getting DuplicateItemException when duplicate Primary keys are inserted

Write df_dyn_target_1 into Dynamo database

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