optimize work horse initialization by configuration mappers on the wo…

…rker process (#4314)

redash/cli/rq.py

@@ -6,6 +6,7 @@
 from click import argument
 from flask.cli import AppGroup
 from rq import Connection, Worker
+from sqlalchemy.orm import configure_mappers
 
 from redash import rq_redis_connection
 from redash.schedule import rq_scheduler, schedule_periodic_jobs
@@ -22,6 +23,11 @@ def scheduler():
 @manager.command()
 @argument('queues', nargs=-1)
 def worker(queues='default'):
+    # Configure any SQLAlchemy mappers loaded until now so that the mapping configuration 
+    # will already be available to the forked work horses and they won't need 
+    # to spend valuable time re-doing that on every fork.
+    configure_mappers()
+
     if not queues:
         queues = ('default',)
     with Connection(rq_redis_connection):