StatefulDoFnRunner creates GC timers for every record

Hi 

So currently the StatefulParDoFn create timers for all the records.
https://github.com/apache/beam/blob/master/runners/core-java/src/main/java/org/apache/beam/runners/core/StatefulDoFnRunner.java#L211

This becomes a problem if you are using GlobalWindows for streaming where these timers get created and never get closed since the window will never close.

This is a problem especially if your memory bound in rocksDB where these timers take up potential space and sloe the pipelines considerably.

Was wondering that if the pipeline runs in global windows we should avoid adding timers to it at all?