Fix 500 error of stats page when cache isn't ready

Signed-off-by: Alfredos-Panagiotis Damkalis <fredy@fredy.gr>

db/base/tasks.py

@@ -10,6 +10,7 @@ from celery import shared_task
 from django.conf import settings
 from django.contrib.auth import get_user_model
 from django.contrib.sites.models import Site
+from django.core.cache import cache
 from django.core.exceptions import ValidationError
 from django.core.files import File
 from django.core.mail import send_mail
@@ -30,6 +31,12 @@ LOGGER = logging.getLogger('db')
 CONTEXT = zmq.Context()
 
 
+def delay_task_with_lock(task, lock_id, lock_expiration, *args):
+    """Ensure unique run of a task by aquiring lock"""
+    if cache.add('{0}-{1}'.format(task.name, lock_id), '', lock_expiration):
+        task.delay(*args)
+
+
 @shared_task
 def check_celery():
     """Dummy celery task to check that everything runs smoothly."""

db/base/tests.py

@@ -279,7 +279,7 @@ class PopulatedDBTest(TestCase):
         # refresh statistics first
         refresh = self.client.get('/statistics/')
         response = self.client.get('/stats/')
-        assertContains(response, 'Total Satellites')
+        assertContains(response, 'calculation')
 
 
 def test_robots(client):

db/base/views.py

@@ -11,7 +11,6 @@ from django.contrib.auth.mixins import LoginRequiredMixin
 from django.core.cache import cache
 from django.core.exceptions import ObjectDoesNotExist
 from django.core.paginator import Paginator
-from django.db import OperationalError
 from django.db.models import Count, Max, Prefetch, Q
 from django.http import HttpResponse, HttpResponseServerError, JsonResponse
 from django.shortcuts import get_object_or_404, redirect, render
@@ -24,8 +23,9 @@ from db.base.forms import MergeSatellitesForm, SatelliteCreateForm, SatelliteUpd
 from db.base.helpers import get_api_token
 from db.base.models import DemodData, Satellite, SatelliteEntry, SatelliteIdentifier, \
     SatelliteSuggestion, Transmitter, TransmitterEntry, TransmitterSuggestion
-from db.base.tasks import export_frames, notify_suggestion
+from db.base.tasks import background_cache_statistics, delay_task_with_lock, export_frames, \
-from db.base.utils import cache_statistics, millify, read_influx
+    notify_suggestion
+from db.base.utils import millify, read_influx
 
 LOGGER = logging.getLogger('db')
 
@@ -334,18 +334,15 @@ def search(request):
 def stats(request):
     """View to render stats page.
 
-    :returns: base/stats.html
+    :returns: base/stats.html or base/calc-stats.html
     """
     cached_satellites = []
     ids = cache.get('satellites_ids')
     observers = cache.get('stats_observers')
     if not ids or not observers:
-        try:
+        delay_task_with_lock(background_cache_statistics, 1, 3600)
-            cache_statistics()
+        return render(request, 'base/calc-stats.html')
-            ids = cache.get('satellites_ids')
+
-            observers = cache.get('stats_observers')
-        except OperationalError:
-            pass
     for sid in ids:
         stat = cache.get(sid)
         cached_satellites.append(stat)
@@ -359,13 +356,12 @@ def stats(request):
 
 
 def statistics(request):
-    """Triggers a refresh of cached statistics if the cache does not exist
+    """Return transmitter cached statistics if the cache exist
 
     :returns: JsonResponse of statistics
     """
     cached_stats = cache.get('stats_transmitters')
     if not cached_stats:
-        cache_statistics()
         cached_stats = []
     return JsonResponse(cached_stats, safe=False)
 

db/templates/base/calc-stats.html

@@ -0,0 +1,38 @@
+{% extends "base.html" %}
+
+{% load tags %}
+{% load static %}
+
+{% block title %} - Stats{% endblock %}
+
+{% block top-menu-left %}
+<span class="h4 mb-0 mr-3 text-truncate d-none d-md-block">Statistics</span>
+{% endblock %}
+
+{% block top %}
+<span class="h4 mb-0">Statistics</span>
+{% endblock %}
+
+{% block content %}
+<!-- SatNOGS DB Calculating Stats -->
+<div class="container-fluid">
+  <div class="row justify-content-center">
+    <div class="col-md-9">
+      <div class="card card-info first-card">
+        <div class="card-header card-satnogs-header">
+          Statistics
+        </div>
+        <div class="card-body">
+          <p>
+              Statistics calculation is in progress and it may take several minutes to complete.
+          </p>
+          <p>
+              Please come back later!
+          </p>
+        </div>
+      </div>
+    </div>
+  </div>
+</div>
+{% endblock %}
+