run_transaction session leak

We just switched over from using db.sessions.commit() to using run_transaction as per the diff:
https://github.com/cockroachdb/examples-python/commit/4fecdf17d1def80b349bd84e58ec042f997fcdcf

After making this change in our test environment after a little bit the api continues to get slower and eventually become completely bound up.

The following error eventually prints out: sqlalchemy.exc.TimeoutError: QueuePool limit of size 5 overflow 20 reached

If there some type of clean up that needs to occur? Or is this a sign of something else?