I'm building a high-volume Beam pipeline using PubsubIO and running into some concerns over performance and delivery semantics, prompting me to want to better understand the implementation. Reading through the library, PubsubIO appears to be a completely separate implementation of Pubsub client behavior from Google's own Java client. As a developer trying to read and understand the implementation, this is a significant hurdle, since any previous knowledge of the Google library is not applicable and is potentially at odds with what's in PubsubIO.
Why doesn't beam use the Google clients for PubsubIO, BigQueryIO, etc.? Is it for historical reasons? Is there difficulty in packaging and integration of the Google clients? Or are the needs for Beam just substantially different from what the Google libraries provide?
