Add celery_once

arkindex/documents/tasks.py

 from celery import shared_task
+from celery_once import QueueOnce
 from django.conf import settings
 from arkindex.documents.models import Element, Act, Transcription
 from arkindex.documents.indexer import Indexer
 
 
-@shared_task
+@shared_task(base=QueueOnce, once={'graceful': True})
 def refresh_db_cache():
     '''
     Refresh materialized views
@@ -12,7 +13,7 @@ def refresh_db_cache():
     Element.objects.refresh_cache()
 
 
-@shared_task
+@shared_task(base=QueueOnce, once={'graceful': True})
 def reindex_acts():
     '''
     Reindex all acts
@@ -22,7 +23,7 @@ def reindex_acts():
     indexer.run_index(settings.ES_INDEX_ACTS, Act.INDEX_TYPE, acts, bulk_size=100)
 
 
-@shared_task
+@shared_task(base=QueueOnce, once={'graceful': True})
 def reindex_transcriptions():
     '''
     Reindex all transcriptions

arkindex/project/celery.py

 from __future__ import absolute_import, unicode_literals
 import os
 from celery import Celery
+from django.conf import settings
 
 # set the default Django settings module for the 'celery' program.
 os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'arkindex.project.settings')
@@ -12,6 +13,7 @@ app = Celery('arkindex')
 # - namespace='CELERY' means all celery-related configuration keys
 #   should have a `CELERY_` prefix.
 app.config_from_object('django.conf:settings', namespace='CELERY')
+app.conf.ONCE = settings.CELERY_ONCE
 
 # Load task modules from all registered Django app configs.
 app.autodiscover_tasks()

arkindex/project/settings.py

@@ -268,6 +268,13 @@ LOGGING = {
 # Async Workers
 CELERY_BROKER_URL = os.environ.get('QUEUE_URL', 'redis://localhost:6379/0')
 CELERY_RESULT_BACKEND = os.environ.get('QUEUE_URL', 'redis://localhost:6379/0')
+CELERY_ONCE = {
+    'backend': 'celery_once.backends.Redis',
+    'settings': {
+        'url': os.environ.get('QUEUE_URL', 'redis://localhost:6379/0'),
+        'default_timeout': 3600,
+    }
+}
 
 # Email
 if os.environ.get('EMAIL_HOST'):

requirements.txt

 celery==4.1.1
+celery_once==2.0.0
 certifi==2017.7.27.1
 chardet==3.0.4
 Django==2.0