Reduce image server statistics to three SQL queries

arkindex/documents/management/commands/telegraf.py

@@ -4,7 +4,7 @@ from django.conf import settings
 from django.db.models import Count
 from django.utils.text import slugify
 from arkindex.documents.models import Element, ElementType, Transcription, Corpus
-from arkindex.images.models import ImageServer, ImageStatus
+from arkindex.images.models import ImageServer, ImageStatus, Image
 from urllib.parse import urljoin
 import time
 import requests
@@ -64,13 +64,26 @@ class Command(BaseCommand):
                 with_transcriptions=vol_with_transcriptions_count.get(corpus.id, 0),
             )
 
+        # Image server statistics, in three SQL queries
+        checked_counts = dict(
+            Image.objects
+                 .filter(status=ImageStatus.Checked)
+                 .values_list('server')
+                 .annotate(Count('server'))
+        )
+        error_counts = dict(
+            Image.objects
+                 .filter(status=ImageStatus.Error)
+                 .values_list('server')
+                 .annotate(Count('server'))
+        )
         for server in ImageServer.objects.annotate(img_total=Count('images')):
             self.output(
                 'images',
                 tags={'imageserver': server.grafana_tag},
                 total=server.img_total,
-                checked=server.images.filter(status=ImageStatus.Checked).count(),
-                errors=server.images.filter(status=ImageStatus.Error).count(),
+                checked=checked_counts.get(server.id, 0),
+                errors=error_counts.get(server.id, 0),
             )
 
     def dict_to_str(self, data):