Merge pull request #6527 from Gallaecio/dont-throttle-meta

Replace Slot.throttle with Request.meta['dont_throttle']

docs/topics/autothrottle.rst

@@ -21,9 +21,14 @@ Design goals
 How it works
 ============
 
-AutoThrottle extension adjusts download delays dynamically to make spider send
-:setting:`AUTOTHROTTLE_TARGET_CONCURRENCY` concurrent requests on average
-to each remote website.
+Scrapy allows defining the concurrency and delay of different download slots,
+e.g. through the :setting:`DOWNLOAD_SLOTS` setting. By default requests are
+assigned to slots based on their URL domain, although it is possible to
+customize the download slot of any request.
+
+The AutoThrottle extension adjusts the delay of each download slot dynamically,
+to make your spider send :setting:`AUTOTHROTTLE_TARGET_CONCURRENCY` concurrent
+requests on average to each remote website.
 
 It uses download latency to compute the delays. The main idea is the
 following: if a server needs ``latency`` seconds to respond, a client
@@ -47,18 +52,6 @@ effect, but there are some important differences:
 
 AutoThrottle doesn't have these issues.
 
-Disabling throttling on a downloader slot
-=========================================
-
-It is possible to disable AutoThrottle for a specific download slot at run time
-by setting its ``throttle`` attribute to ``False``, e.g. using
-:setting:`DOWNLOAD_SLOTS`.
-
-Note, however, that AutoThrottle still determines the starting delay of every
-slot by setting the ``download_delay`` attribute on the running spider. You
-might want to set a custom value for the ``delay`` attribute of the slot, e.g.
-using :setting:`DOWNLOAD_SLOTS`.
-
 Throttling algorithm
 ====================
 
@@ -92,6 +85,33 @@ callback, for example, and unable to attend downloads. However, these latencies
 should still give a reasonable estimate of how busy Scrapy (and ultimately, the
 server) is, and this extension builds on that premise.
 
+.. reqmeta:: autothrottle_dont_adjust_delay
+
+Prevent specific requests from triggering slot delay adjustments
+================================================================
+
+AutoThrottle adjusts the delay of download slots based on the latencies of
+responses that belong to that download slot. The only exceptions are non-200
+responses, which are only taken into account to increase that delay, but
+ignored if they would decrease that delay.
+
+You can also set the ``autothrottle_dont_adjust_delay`` request metadata key to
+``True`` in any request to prevent its response latency from impacting the
+delay of its download slot:
+
+.. code-block:: python
+
+    from scrapy import Request
+
+    Request("https://example.com", meta={"autothrottle_dont_adjust_delay": True})
+
+Note, however, that AutoThrottle still determines the starting delay of every
+download slot by setting the ``download_delay`` attribute on the running
+spider. If you want AutoThrottle not to impact a download slot at all, in
+addition to setting this meta key in all requests that use that download slot,
+you might want to set a custom value for the ``delay`` attribute of that
+download slot, e.g. using :setting:`DOWNLOAD_SLOTS`.
+
 Settings
 ========
 

docs/topics/request-response.rst

@@ -668,6 +668,7 @@ are some special keys recognized by Scrapy and its built-in extensions.
 
 Those are:
 
+* :reqmeta:`autothrottle_dont_adjust_delay`
 * :reqmeta:`bindaddress`
 * :reqmeta:`cookiejar`
 * :reqmeta:`dont_cache`

docs/topics/settings.rst

@@ -845,12 +845,7 @@ Allows to define concurrency/delay parameters on per slot (domain) basis:
     .. code-block:: python
 
         DOWNLOAD_SLOTS = {
-            "quotes.toscrape.com": {
-                "concurrency": 1,
-                "delay": 2,
-                "randomize_delay": False,
-                "throttle": False,
-            },
+            "quotes.toscrape.com": {"concurrency": 1, "delay": 2, "randomize_delay": False},
             "books.toscrape.com": {"delay": 3, "randomize_delay": False},
         }
 
@@ -862,9 +857,6 @@ Allows to define concurrency/delay parameters on per slot (domain) basis:
     -   :setting:`CONCURRENT_REQUESTS_PER_DOMAIN`: ``concurrency``
     -   :setting:`RANDOMIZE_DOWNLOAD_DELAY`: ``randomize_delay``
 
-    There is no global setting for ``throttle``, whose default value is
-    ``None``.
-
 
 .. setting:: DOWNLOAD_TIMEOUT
 

scrapy/core/downloader/__init__.py

@@ -36,13 +36,10 @@ class Slot:
         concurrency: int,
         delay: float,
         randomize_delay: bool,
-        *,
-        throttle: bool | None = None,
     ):
         self.concurrency: int = concurrency
         self.delay: float = delay
         self.randomize_delay: bool = randomize_delay
-        self.throttle = throttle
 
         self.active: set[Request] = set()
         self.queue: deque[tuple[Request, Deferred[Response]]] = deque()
@@ -67,15 +64,13 @@ class Slot:
         return (
             f"{cls_name}(concurrency={self.concurrency!r}, "
             f"delay={self.delay:.2f}, "
-            f"randomize_delay={self.randomize_delay!r}, "
-            f"throttle={self.throttle!r})"
+            f"randomize_delay={self.randomize_delay!r})"
         )
 
     def __str__(self) -> str:
         return (
             f"<downloader.Slot concurrency={self.concurrency!r} "
             f"delay={self.delay:.2f} randomize_delay={self.randomize_delay!r} "
-            f"throttle={self.throttle!r} "
             f"len(active)={len(self.active)} len(queue)={len(self.queue)} "
             f"len(transferring)={len(self.transferring)} "
             f"lastseen={datetime.fromtimestamp(self.lastseen).isoformat()}>"
@@ -146,8 +141,7 @@ class Downloader:
                 slot_settings.get("delay", delay),
             )
             randomize_delay = slot_settings.get("randomize_delay", self.randomize_delay)
-            throttle = slot_settings.get("throttle", None)
-            new_slot = Slot(conc, delay, randomize_delay, throttle=throttle)
+            new_slot = Slot(conc, delay, randomize_delay)
             self.slots[key] = new_slot
 
         return key, self.slots[key]

scrapy/extensions/throttle.py

@@ -64,7 +64,11 @@ class AutoThrottle:
     ) -> None:
         key, slot = self._get_slot(request, spider)
         latency = request.meta.get("download_latency")
-        if latency is None or slot is None or slot.throttle is False:
+        if (
+            latency is None
+            or slot is None
+            or request.meta.get("autothrottle_dont_adjust_delay", False) is True
+        ):
             return
 
         olddelay = slot.delay

tests/test_core_downloader.py

@@ -8,5 +8,5 @@ class SlotTest(unittest.TestCase):
         slot = Slot(concurrency=8, delay=0.1, randomize_delay=True)
         self.assertEqual(
             repr(slot),
-            "Slot(concurrency=8, delay=0.10, randomize_delay=True, throttle=None)",
+            "Slot(concurrency=8, delay=0.10, randomize_delay=True)",
         )

tests/test_downloaderslotssettings.py

@@ -80,7 +80,6 @@ def test_params():
         "concurrency": 1,
         "delay": 2,
         "randomize_delay": False,
-        "throttle": False,
     }
     settings = {
         "DOWNLOAD_SLOTS": {

tests/test_extension_throttle.py

@@ -157,17 +157,24 @@ def test_startdelay_definition(min_spider, min_setting, start_setting, expected)
 
 
 @pytest.mark.parametrize(
-    ("meta", "slot", "throttle"),
+    ("meta", "slot"),
     (
-        ({}, None, None),
-        ({"download_latency": 1.0}, None, None),
-        ({"download_slot": "foo"}, None, None),
-        ({"download_slot": "foo"}, "foo", None),
-        ({"download_latency": 1.0, "download_slot": "foo"}, None, None),
-        ({"download_latency": 1.0, "download_slot": "foo"}, "foo", False),
+        ({}, None),
+        ({"download_latency": 1.0}, None),
+        ({"download_slot": "foo"}, None),
+        ({"download_slot": "foo"}, "foo"),
+        ({"download_latency": 1.0, "download_slot": "foo"}, None),
+        (
+            {
+                "download_latency": 1.0,
+                "download_slot": "foo",
+                "autothrottle_dont_adjust_delay": True,
+            },
+            "foo",
+        ),
     ),
 )
-def test_skipped(meta, slot, throttle):
+def test_skipped(meta, slot):
     crawler = get_crawler()
     at = build_from_crawler(AutoThrottle, crawler)
     spider = TestSpider()
@@ -178,9 +185,7 @@ def test_skipped(meta, slot, throttle):
     crawler.engine.downloader = Mock()
     crawler.engine.downloader.slots = {}
     if slot is not None:
-        _slot = Mock()
-        _slot.throttle = throttle
-        crawler.engine.downloader.slots[slot] = _slot
+        crawler.engine.downloader.slots[slot] = object()
     at._adjust_delay = None  # Raise exception if called.
 
     at._response_downloaded(None, request, spider)