fix(llm): skip the database-wide iterative_scan ALTER once it is in place

hnsw.iterative_scan = relaxed_order is already set on the llm database
(pg_db_role_setting), but migrate re-issued ALTER DATABASE on every
index run as the llm role, which may not, and postgres logged two
permission ERRORs each time. migrate now checks the setting first.
Verified live: the check sees it, a migrate run logs nothing.

src/llm/migrate.py

@@ -89,6 +89,12 @@ _METADATA_INDEX_DDL = [
 # — the API's pooled connections included — inherits it without having
 # to load the extension's GUCs first.
 ITERATIVE_SCAN_DDL = "ALTER DATABASE {db} SET hnsw.iterative_scan = 'relaxed_order'"
+_ITERATIVE_SCAN_SET_SQL = (
+    "SELECT EXISTS (SELECT 1 FROM pg_db_role_setting s "
+    "JOIN pg_database d ON d.oid = s.setdatabase "
+    "WHERE d.datname = current_database() AND s.setrole = 0 "
+    "AND 'hnsw.iterative_scan=relaxed_order' = ANY (s.setconfig))"
+)
 
 
 def migrate(engine: Engine) -> None:
@@ -109,6 +115,10 @@ def ensure_iterative_scan(engine: Engine) -> None:
     try:
         with engine.begin() as conn:
             db = conn.execute(text("SELECT current_database()")).scalar()
+            # Already in place (set once by a role that may): re-issuing it
+            # as the llm role only logs a permission ERROR in postgres.
+            if conn.execute(text(_ITERATIVE_SCAN_SET_SQL)).scalar():
+                return
             conn.execute(text(ITERATIVE_SCAN_DDL.format(db=db)))
     except Exception as exc:  # noqa: BLE001 — the llm role usually may not ALTER DATABASE
         # every connection also SETs it itself (llm.index.set_iterative_scan),

tests/llm/test_migrate.py

@@ -88,7 +88,15 @@ class TestIterativeScan:
 
         engine = MagicMock()
         conn = engine.begin.return_value.__enter__.return_value
-        conn.execute.return_value.scalar.return_value = "llm"
+
+        def answer(stmt, *a, **k):
+            r = MagicMock()
+            r.scalar.return_value = (
+                False if "pg_db_role_setting" in str(stmt) else "llm"
+            )
+            return r
+
+        conn.execute.side_effect = answer
         migrate(engine)
         sql = [str(c.args[0]) for c in conn.execute.call_args_list]
         assert any(
@@ -96,6 +104,26 @@ class TestIterativeScan:
             for q in sql
         )
 
+    def test_already_set_database_wide_issues_no_alter(self):
+        # The llm role may not ALTER DATABASE; re-issuing it on every index
+        # run only logged two permission ERRORs in postgres per run.
+        from unittest.mock import MagicMock
+
+        from llm.migrate import ensure_iterative_scan
+
+        engine = MagicMock()
+        conn = engine.begin.return_value.__enter__.return_value
+
+        def answer(stmt, *a, **k):
+            r = MagicMock()
+            r.scalar.return_value = True if "pg_db_role_setting" in str(stmt) else "llm"
+            return r
+
+        conn.execute.side_effect = answer
+        ensure_iterative_scan(engine)
+        sql = [str(c.args[0]) for c in conn.execute.call_args_list]
+        assert not any("ALTER DATABASE" in q for q in sql)
+
     def test_failure_is_a_warning_not_an_error(self, caplog):
         from unittest.mock import MagicMock