# Considerations and limitations
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Consider the following points when you use user defined function (UDFs) in Athena.
+ **Built-in Athena functions** – Built-in functions in Athena are designed to be highly performant. We recommend that you use built-in functions over UDFs when possible. For more information about built-in functions, see [Functions in Amazon Athena](functions.md).
+ **Scalar UDFs only** – Athena only supports scalar UDFs, which process one row at a time and return a single column value. Athena passes a batch of rows, potentially in parallel, to the UDF each time it invokes Lambda. When designing UDFs and queries, be mindful of the potential impact to network traffic of this processing.
+ **UDF handler functions use abbreviated format** – Use abbreviated format (not full format), for your UDF functions (for example, `package.Class` instead of `package.Class::method`). 
+ **UDF methods must be lowercase** – UDF methods must be in lowercase; camel case is not permitted. 
+ **UDF methods require parameters** – UDF methods must have at least one input parameter. Attempting to invoke a UDF defined without input parameters causes a runtime exception. UDFs are meant to perform functions against data records, but a UDF without arguments takes in no data, so an exception occurs.
+ **Java runtime support** – Currently, Athena UDFs support the Java 8, Java 11, and Java 17 runtimes for Lambda. For more information, see [Building Lambda functions with Java](https://docs.aws.amazon.com/lambda/latest/dg/lambda-java.html) in the *AWS Lambda Developer Guide*.
**Note**  
 For Java 17, you must set the value of `JAVA_TOOL_OPTIONS` environment variable as `--add-opens=java.base/java.nio=ALL-UNNAMED` in your Lambda. 
+ **IAM permissions** – To run and create UDF query statements in Athena, the IAM principal running the query must be allowed to perform actions in addition to Athena functions. For more information, see [Allow access to Athena UDFs: Example policies](udf-iam-access.md).
+ **Lambda quotas** – Lambda quotas apply to UDFs. For more information, see [Lambda quotas](https://docs.aws.amazon.com/lambda/latest/dg/limits.html) in the *AWS Lambda Developer Guide*.
+ **Row-level filtering** – Lake Formation row-level filtering is not supported for UDFs. 
+ **Views** – You cannot use views with UDFs. 
+ **Known issues** – For the most up-to-date list of known issues, see [Limitations and issues](https://github.com/awslabs/aws-athena-query-federation/wiki/Limitations_And_Issues) in the awslabs/aws-athena-query-federation section of GitHub.