Add composite index main_detection(occurrence_id, timestamp DESC)

ami/main/migrations/0084_index_detection_occurrence_timestamp.py

@@ -0,0 +1,21 @@
+from django.contrib.postgres.operations import AddIndexConcurrently
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("main", "0083_dedupe_taxalist_names"),
+    ]
+
+    # AddIndexConcurrently requires running outside a transaction.
+    atomic = False
+
+    operations = [
+        AddIndexConcurrently(
+            model_name="detection",
+            index=models.Index(
+                fields=["occurrence", "-timestamp"],
+                name="detection_occurrence_ts_desc",
+            ),
+        ),
+    ]

ami/main/models.py

@@ -2778,6 +2778,16 @@ class Meta:
             "frame_num",
             "timestamp",
         ]
+        indexes = [
+            # Supports /captures/ list ordering and joins from Occurrence to
+            # its detections by (occurrence_id, timestamp DESC). Django's FK
+            # index alone is on occurrence_id, which forces a sort on a large
+            # row set after the join.
+            models.Index(
+                fields=["occurrence", "-timestamp"],
+                name="detection_occurrence_ts_desc",
+            ),
+        ]
 
     def best_classification(self):
         # @TODO where is this used?