Prioritize other requests over start requests

scrapy/core/scheduler.py

@@ -173,8 +173,8 @@ class Scheduler(BaseScheduler):
 
     :ref:`Start requests <start-requests>` are sent in the order they are
     yielded from :meth:`~scrapy.Spider.start`, and given the same
-    :attr:`~scrapy.http.Request.priority`, start requests take precedence over
-    other requests.
+    :attr:`~scrapy.http.Request.priority`, other requests take precedence over
+    start requests.
 
     You can set :setting:`SCHEDULER_START_MEMORY_QUEUE` and
     :setting:`SCHEDULER_START_DISK_QUEUE` to ``None`` to handle start requests

scrapy/pqueues.py

@@ -160,28 +160,32 @@ class ScrapyPriorityQueue:
 
     def pop(self) -> Request | None:
         while self.curprio is not None:
-            if self._start_queues:
-                try:
-                    q = self._start_queues[self.curprio]
-                except KeyError:
-                    pass
-                else:
-                    m = q.pop()
-                    if not q:
-                        del self._start_queues[self.curprio]
-                        q.close()
-                    return m
             try:
                 q = self.queues[self.curprio]
             except KeyError:
-                self._update_curprio()
+                pass
             else:
                 m = q.pop()
                 if not q:
                     del self.queues[self.curprio]
                     q.close()
-                    self._update_curprio()
+                    if not self._start_queues:
+                        self._update_curprio()
                 return m
+            if self._start_queues:
+                try:
+                    q = self._start_queues[self.curprio]
+                except KeyError:
+                    self._update_curprio()
+                else:
+                    m = q.pop()
+                    if not q:
+                        del self._start_queues[self.curprio]
+                        q.close()
+                        self._update_curprio()
+                    return m
+            else:
+                self._update_curprio()
         return None
 
     def _update_curprio(self) -> None:

tests/test_engine_loop.py

@@ -189,9 +189,9 @@ class RequestSendOrderTestCase(TestCase):
 
     @deferred_f_from_coro_f
     async def test_default(self):
-        """By default, start requests take priority over callback requests and
+        """By default, callback requests take priority over start requests and
         are sent in order. Priority matters, but given the same priority, a
-        start request takes precedence."""
+        callback request takes precedence."""
         nums = [1, 2, 3, 4, 5, 6]
         response_seconds = 0
         download_slots = 1
@@ -207,13 +207,13 @@ class RequestSendOrderTestCase(TestCase):
             yield _request(1)
 
             for request in (
-                _request(4, priority=1),
-                _request(6),
+                _request(2, priority=1),
+                _request(5),
             ):
                 spider.crawler.engine._slot.scheduler.enqueue_request(request)
-            yield _request(5)
-            yield _request(2, priority=1)
+            yield _request(6)
             yield _request(3, priority=1)
+            yield _request(4, priority=1)
 
         def parse(spider, response):
             return
@@ -249,13 +249,13 @@ class RequestSendOrderTestCase(TestCase):
             yield _request(1)
 
             for request in (
-                _request(4, priority=1),
-                _request(6),
+                _request(2, priority=1),
+                _request(5),
             ):
                 spider.crawler.engine._slot.scheduler.enqueue_request(request)
-            yield _request(5)
+            yield _request(6)
+            yield _request(4, priority=1)
             yield _request(3, priority=1)
-            yield _request(2, priority=1)
 
         def parse(spider, response):
             return