fix: slow responses on schema cache reload

CHANGELOG.md

@@ -24,6 +24,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
  - #3237, Dump media handlers and timezones with --dump-schema - @wolfgangwalther
  - #3323, #3324, Don't hide error on LISTEN channel failure - @steve-chavez
  - #3330, Incorrect admin server `/ready` response on slow schema cache loads - @steve-chavez
+ - #3327, Fix slow responses on schema cache reloads - @steve-chavez
 
 ### Deprecated
 

src/PostgREST/AppState.hs

@@ -319,10 +319,12 @@ loadSchemaCache appState observer = do
           return SCOnRetry
 
     Right sCache -> do
-      putSchemaCache appState $ Just sCache
       observer $ SchemaCacheQueriedObs resultTime
       (t, _) <- timeItT $ observer $ SchemaCacheSummaryObs sCache
       observer $ SchemaCacheLoadedObs t
+      -- it's important to update AppState schema cache only once it has been fully evaluated before (this will be done by the observer above)
+      -- otherwise requests will wait for the schema cache to be loaded
+      putSchemaCache appState $ Just sCache
       putSchemaCacheLoaded appState True
       return SCLoaded
 

test/io/big_schema.sql

@@ -11384,3 +11384,7 @@ GRANT USAGE ON SCHEMA apflora TO postgrest_test_anonymous;
 
 GRANT ALL PRIVILEGES ON ALL TABLES IN SCHEMA apflora
 TO postgrest_test_anonymous;
+
+create or replace function apflora.notify_pgrst() returns void as $$
+  notify pgrst;
+$$ language sql;

test/io/test_big_schema.py

@@ -18,7 +18,7 @@ def test_first_request_succeeds(defaultenv):
         "PGRST_SERVER_TIMING_ENABLED": "true",
     }
 
-    with run(env=env, wait_max_seconds=20) as postgrest:
+    with run(env=env, wait_max_seconds=30) as postgrest:
         response = postgrest.session.get("/tpopmassn?select=*,tpop(*)")
         assert response.status_code == 200
 
@@ -27,8 +27,8 @@ def test_first_request_succeeds(defaultenv):
         assert plan_dur < 2.0
 
 
-def test_requests_wait_for_schema_cache_to_be_loaded(defaultenv):
+def test_requests_do_not_wait_for_schema_cache_reload(defaultenv):
-    "requests that use the schema cache (e.g. resource embedding) wait for schema cache to be loaded"
+    "requests that use the schema cache (e.g. resource embedding) do not wait for the schema cache to reload"
 
     env = {
         **defaultenv,
@@ -38,15 +38,20 @@ def test_requests_wait_for_schema_cache_to_be_loaded(defaultenv):
         "PGRST_SERVER_TIMING_ENABLED": "true",
     }
 
-    with run(env=env, wait_for_readiness=False) as postgrest:
+    with run(env=env, wait_max_seconds=30) as postgrest:
-        time.sleep(1.5)  # manually wait for schema cache to start loading
+        # reload the schema cache
+        response = postgrest.session.get("/rpc/notify_pgrst")
+        assert response.status_code == 204
+
+        time.sleep(1.5)  # wait for schema cache to start reloading
 
         response = postgrest.session.get("/tpopmassn?select=*,tpop(*)")
         assert response.status_code == 200
 
+        # response should be fast
         server_timings = parse_server_timings_header(response.headers["Server-Timing"])
         plan_dur = server_timings["plan"]
-        assert plan_dur > 10000.0
+        assert plan_dur < 2.0
 
 
 # TODO: This test fails now because of https://github.com/PostgREST/postgrest/pull/2122