🔧(backend) add DB_PSYCOPG_POOL_ENABLED settings

The psycopg pool config was enabled by default forcing its usage. Using
psycopg pool can be difficult, finding the good configuration take time.
By default its usage should be disable and the maintainer of the
instance should decide to enable it or not.

src/backend/core/tests/test_settings.py

@@ -28,3 +28,39 @@ def test_invalid_settings_oidc_email_configuration():
         "Both OIDC_FALLBACK_TO_EMAIL_FOR_IDENTIFICATION and "
         "OIDC_ALLOW_DUPLICATE_EMAILS cannot be set to True simultaneously. "
     )
+
+
+def test_settings_psycopg_pool_not_enabled():
+    """
+    Test that not changing DB_PSYCOPG_POOL_ENABLED should not configure psycopg in the DATABASES
+    settings.
+    """
+
+    class TestSettings(Base):
+        """Fake test settings without enabling psycopg"""
+
+    TestSettings.post_setup()
+
+    assert TestSettings.DATABASES["default"].get("OPTIONS") == {}
+
+
+def test_settings_psycopg_pool_enabled(monkeypatch):
+    """
+    Test when DB_PSYCOPG_POOL_ENABLED is set to True, the psycopg pool options should be present
+    in the DATABASES OPTIONS.
+    """
+
+    monkeypatch.setenv("DB_PSYCOPG_POOL_ENABLED", "True")
+
+    class TestSettings(Base):
+        """Fake test settings without enabling psycopg"""
+
+    TestSettings.post_setup()
+
+    assert TestSettings.DATABASES["default"].get("OPTIONS") == {
+        "pool": {
+            "min_size": 4,
+            "max_size": None,
+            "timeout": 3,
+        }
+    }

src/backend/impress/settings.py

@@ -99,24 +99,7 @@ class Base(Configuration):
                 "localhost", environ_name="DB_HOST", environ_prefix=None
             ),
             "PORT": values.Value(5432, environ_name="DB_PORT", environ_prefix=None),
-            "OPTIONS": {
-                # https://www.psycopg.org/psycopg3/docs/api/pool.html#psycopg_pool.ConnectionPool
-                "pool": {
-                    "min_size": values.IntegerValue(
-                        4, environ_name="DB_PSYCOPG_POOL_MIN_SIZE", environ_prefix=None
-                    ),
-                    "max_size": values.IntegerValue(
-                        None,
-                        environ_name="DB_PSYCOPG_POOL_MAX_SIZE",
-                        environ_prefix=None,
-                    ),
-                    "timeout": values.IntegerValue(
-                        3,
-                        environ_name="DB_PSYCOPG_POOL_TIMEOUT",
-                        environ_prefix=None,
-                    ),
-                }
-            },
+            # Psycopg pool can be configured in the post_setup method
         }
     }
     DEFAULT_AUTO_FIELD = "django.db.models.AutoField"
@@ -1017,6 +1000,36 @@ class Base(Configuration):
                 "OIDC_ALLOW_DUPLICATE_EMAILS cannot be set to True simultaneously. "
             )
 
+        psycopg_pool_enabled = values.BooleanValue(
+            False, environ_name="DB_PSYCOPG_POOL_ENABLED", environ_prefix=""
+        )
+
+        if psycopg_pool_enabled:
+            cls.DATABASES["default"].update(
+                {
+                    "OPTIONS": {
+                        # https://www.psycopg.org/psycopg3/docs/api/pool.html#psycopg_pool.ConnectionPool
+                        "pool": {
+                            "min_size": values.IntegerValue(
+                                4,
+                                environ_name="DB_PSYCOPG_POOL_MIN_SIZE",
+                                environ_prefix=None,
+                            ),
+                            "max_size": values.IntegerValue(
+                                None,
+                                environ_name="DB_PSYCOPG_POOL_MAX_SIZE",
+                                environ_prefix=None,
+                            ),
+                            "timeout": values.IntegerValue(
+                                3,
+                                environ_name="DB_PSYCOPG_POOL_TIMEOUT",
+                                environ_prefix=None,
+                            ),
+                        }
+                    },
+                }
+            )
+
 
 class Build(Base):
     """Settings used when the application is built.