Apache Cassandra 3.0 introduces user-defined functions (UDFs) allowing users to execute custom code on Cassandra nodes, enhancing functionality without requiring new releases. UDFs can be written in Java and JavaScript, with capabilities to create user-defined aggregates for complex calculations across multiple rows. Permissions for UDF creation and execution are implemented to maintain security, emphasizing the importance of testing and performance optimization.

1. User Defined Functions
… new in Apache Cassandra 3.0
CASSANDRA-7395 + many more…

2. Me, Robert…
• Contribute code to Apache Cassandra (UDFs, row cache + more)
• Help customers to build Cassandra solutions
• Freelancer, Coder
Robert Stupp, Cologne, Germany
@snazy snazy@snazy.de

3. Disclaimer
• Apache Cassandra 3.0 is the next major release
• Everything is under development
• Things may change
• Things may be different in final 3.0 release

4. Apache Cassandra 3.0
• … will bring a lot of cool, new features !
• … will bring a lot of great improvements !
• UDFs is just one of these features :)

5. UDF -
What’s that??

6. UDF
• UDF means User Defined Function
• You write the code that’s executed on Cassandra nodes
• Functions are distributed transparently to the whole cluster
• You may not have to wait for a new release for new functionality :)

7. UDF Characteristics
• „Pure“
• just input parameters
• no state, side effects, dependencies to other code, etc
• Usually deterministic

8. Consider a Java function like…
import nothing;
public final class MyClass
{
public static int myFunction ( int argument )
{
return argument * 42;
}
}
This would be your UDF

9. CREATE FUNCTION sinPlusFoo
(
valueA double,
valueB double
arguments
return type
)
RETURNS double
LANGUAGE java
AS ’return Math.sin(valueA) + valueB;’;
Java works out of the box!
Example
define the UDF language
Java code

10. Next Example
CREATE FUNCTION sin (
value double )
RETURNS double
LANGUAGE javascript
AS ’Math.sin(value);’;
JavaScript works out of the box!
Cassandra 3.0 targets Java8 - so it’s „Nashorn“
JavaScript works, too!
Javascript code

11. JSR 223
• “Scripting for the Java Platform“
• UDFs can be written in Java and JavaScript
• Optionally: Groovy, JRuby, Jython, Scala
• Not: Clojure (JSR 223 implementation’s wrong)

12. Behind the scenes
• Builds Java (or script) source
• Compiles that code (Java class, or compiled script)
• Loads the compiled code
• Migrates the function to all other nodes
• Done - UDF is executable on any node

13. Types for UDFs
• Support for all Cassandra types for arguments and return value
• All means
• Primitives (boolean, int, double, uuid, etc)
• Collections (list, set, map)
• Tuple types, User Defined Types

14. UDF -
For what?

15. UDF invocation
SELECT sumThat ( colA, colB )
Now your application can
sum two values in one row -
or create the sin of a value!
GREAT NEW FEATURES!
Okay - not really…
FROM myTable
WHERE key = ...
SELECT sin ( foo )
FROM myCircle
WHERE pk = ...

16. UDFs are good for…
• UDFs on their own are just „nice to have“
• Nothing you couldn’t do better in your application

17. Real Use Case for UDFs ?

18. User Defined Aggregates !
CASSANDRA-8053

19. User Defined Aggregates
Use UDFs to code your own aggregation functions
(Aggregates are things like SUM, AVG, MIN, MAX, etc)
Aggregates :
consume values from multiple rows &
produce a single result

20. Example
name of the aggregate
function argument types
CREATE AGGREGATE minimum ( int )
STYPE int
SFUNC minimumState;
name of the “state“ UDF
Syntax similar to Postgres.
state type

21. How an aggregate works
SELECT minimum ( val ) FROM foo …
1. Initial state is set to null
2. for each row the state function is called with
current state and column value - returns new state
3. After all rows the aggregate returns the last state

22. More sophisticated
CREATE AGGREGATE average ( int )
SFUNC averageState
STYPE tuple<long,int>
FINALFUNC averageFinal
INITCOND (0, 0);
UDF called after last
row
FINALFUNC + INITCOND are optional initial state value

23. How that aggregate works
SELECT average ( val ) FROM foo …
1. Initial state is set to (0,0)
2. for each row the state function is called with
current state + column value - returns new state
3. After all rows the final function is called with last state
4. final function calculates the aggregate

24. Now everybody can execute evil
code on your cluster :)

25. UDF permissions
• There will be permissions to restrict (allow)
• UDF creation (DDL)
• UDF execution (DML)
CASSANDRA-7557

26. Built in functions
• All known built-in functions are called native functions
• Native functions belong to SYSTEM keyspace
• Native functions cannot be modified (or dropped)
Note: you already know native functions like
now, count, unixtimestampof

27. UDF belong to a keyspace
• User Defined Functions and
• User Defined Aggregate
• belong to a keyspace
• SYSTEM keyspace is searched first for functions
(then the current keyspace)
if function/aggregate is not fully qualified

28. UDF - some final words…
Keep in mind:
• JSR-223 has overhead - Java UDFs are much faster
• Do not allow everyone to create UDFs (in production)
• Keep your UDFs “pure“
• Test your UDFs and user defined aggregates thoroughly

29. For the geeks :)
• UDFs and user defined aggregates are executed on the coordinator node
• Prefer to use Java-UDFs for performance reasons

30. Let a man dream…
UDFs could be useful for…
• Functional indexes
• Partial indexes
• Filtering
• Distributed GROUP BY
• etc etc

31. Q & A
THANK YOU FOR YOUR ATTENTION :)
Robert Stupp, Cologne, Germany
@snazy snazy@snazy.de