Do you have backend examples?

The server side model relies heavily on your backend providing with aggregations/sort/filter e.t.c. Because we can't provide with a sample implementation for each backend, in many cases you will find that you will have to implement this by yourself.

We do however have some reference implementations.

mySql: 

https://www.ag-grid.com/javascript-grid-server-side-model/#example-slice-and-dice-real-server

https://github.com/ag-grid/ag-grid-enterprise-mysql-example

Java + Oracle

https://www.ag-grid.com/oracle-server-side-operations/

Java + Spark

https://www.ag-grid.com/spark-server-side-operations/