feat: Add GIN index on Identity.identifier (#5369)

Author: khvn26

api/environments/identities/migrations/0003_add_idenity_identifier_gin_index.py

@@ -0,0 +1,47 @@
+# Generated by Django 4.2.18 on 2025-04-22 10:15
+
+from django.contrib.postgres.indexes import GinIndex
+from django.contrib.postgres.operations import TrigramExtension
+from django.db import migrations
+import django.contrib.postgres.indexes
+import django.db.models.functions.text
+
+from core.migration_helpers import PostgresOnlyRunSQL
+
+
+_create_index_sql = "CREATE INDEX CONCURRENTLY IF NOT EXISTS identity_identifier_idx ON environments_identity USING GIN (UPPER(identifier) gin_trgm_ops);"
+_create_index_reverse_sql = (
+    "DROP INDEX CONCURRENTLY IF EXISTS identity_identifier_idx;"
+)
+
+
+class Migration(migrations.Migration):
+    atomic = False
+
+    dependencies = [
+        ("identities", "0002_alter_identity_index_together"),
+    ]
+
+    operations = [
+        migrations.SeparateDatabaseAndState(
+            state_operations=[
+                migrations.AddIndex(
+                    model_name="identity",
+                    index=GinIndex(
+                        django.contrib.postgres.indexes.OpClass(
+                            django.db.models.functions.text.Upper("identifier"),
+                            name="gin_trgm_ops",
+                        ),
+                        name="identity_identifier_idx",
+                    ),
+                ),
+            ],
+            database_operations=[
+                TrigramExtension(),
+                PostgresOnlyRunSQL(
+                    sql=_create_index_sql,
+                    reverse_sql=_create_index_reverse_sql,
+                ),
+            ],
+        ),
+    ]

api/environments/identities/models.py

@@ -1,8 +1,10 @@
 import typing
 from itertools import chain
 
+from django.contrib.postgres.indexes import GinIndex, OpClass
 from django.db import models
 from django.db.models import Prefetch, Q
+from django.db.models.functions import Upper
 from django.utils import timezone
 from flag_engine.segments.evaluator import evaluate_identity_in_segment
 
@@ -40,6 +42,12 @@ class Meta:
         # avoid any downtime. If people using MySQL / Oracle have issues with poor performance on the identities table,
         # we can provide them the SQL to add it manually in a small window of downtime.
         index_together = (("environment", "created_date"),)
+        indexes = [
+            GinIndex(
+                OpClass(Upper("identifier"), name="gin_trgm_ops"),
+                name="identity_identifier_idx",
+            ),
+        ]
 
     def natural_key(self):  # type: ignore[no-untyped-def]
         return self.identifier, self.environment.api_key