Hi Swapnil Sarkar ,
Welcome to Microsoft Q&A platform and thanks for posting your question here.
As per my understanding, you have noticed that the NUMBER datatype in Oracle gets converted to Decimal, String (if precision > 28) in the Parquet file. You want to know if that is expected and in case it is , then which resource is responsible to do that.
This is an expected behavior. When you copy data from and to Oracle, interim data type mappings are used within the service . Oracle data types like FLOAT, INTEGER and NUMBER are converted into Decimal, String (if precision > 28)
For more details, kindly check the official documentation : Data type mapping for Oracle
Probably, the conversion is taken care in the oracle connector present in ADF. Since it is increasing the copy duration and impacting the data loads, you can try utilizing the guidance provided in the following documentation to improve the performance while using copy activity : Copy activity performance and scalability guide
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