message: [druid] Fixing issue 3894  multi-processing w/ Gunicorn
diff: @@ -4,7 +4,7 @@ from copy import deepcopy
  from datetime import datetime, timedelta
  import json
  import logging
  -from multiprocessing import Pool
  +from multiprocessing.pool import ThreadPool
  from dateutil.parser import parse as dparse
  from flask import escape, Markup
  @@ -157,7 +157,7 @@ class DruidCluster(Model, AuditMixinNullable):
  session.flush()
  # Prepare multithreaded executation
  - pool = Pool()
  + pool = ThreadPool()
  ds_refresh = list(ds_map.values())
  metadata = pool.map(_fetch_metadata_for, ds_refresh)
  pool.close()
  