Update the FAQ

docs/conf.py

@@ -177,3 +177,21 @@ hoverxref_role_types = {
 hoverxref_roles = ["command", "reqmeta", "setting", "signal"]
 
 default_dark_mode = False
+
+# -- setup -------------------------------------------------------------------
+
+
+def setup(app):
+    # https://stackoverflow.com/a/58982001
+    for cls_name in (
+        "FifoMemoryQueue",
+        "LifoMemoryQueue",
+        "PickleFifoDiskQueue",
+        "PickleLifoDiskQueue",
+        "MarshalFifoDiskQueue",
+        "MarshalLifoDiskQueue",
+    ):
+        import scrapy.squeues
+
+        cls = getattr(scrapy.squeues, cls_name)
+        cls.__name__ = cls_name

docs/faq.rst

@@ -105,27 +105,22 @@ By default, Scrapy uses a `LIFO`_ queue for storing pending requests, which
 basically means that it crawls in `DFO order`_. This order is more convenient
 in most cases.
 
-If you do want to crawl in true `BFO order`_, you can do it by
-setting the following settings:
+To crawl in `BFO order`_:
 
-.. code-block:: python
+-   Set :setting:`DEPTH_PRIORITY` to ``1``.
 
-    DEPTH_PRIORITY = 1
-    SCHEDULER_DISK_QUEUE = "scrapy.squeues.PickleFifoDiskQueue"
-    SCHEDULER_MEMORY_QUEUE = "scrapy.squeues.FifoMemoryQueue"
+-   Set :setting:`SCHEDULER_MEMORY_QUEUE` to
+    :class:`~scrapy.squeues.FifoMemoryQueue`.
 
-While pending requests are below the configured values of
-:setting:`CONCURRENT_REQUESTS`, :setting:`CONCURRENT_REQUESTS_PER_DOMAIN` or
-:setting:`CONCURRENT_REQUESTS_PER_IP`, those requests are sent
-concurrently. As a result, the first few requests of a crawl rarely follow the
-desired order. Lowering those settings to ``1`` enforces the desired order, but
-it significantly slows down the crawl as a whole.
+-   Set :setting:`SCHEDULER_DISK_QUEUE` to
+    :class:`~scrapy.squeues.PickleFifoDiskQueue`.
 
+-   :ref:`Send start requests before other requests <start-requests-order>`.
 
 My Scrapy crawler has memory leaks. What can I do?
 --------------------------------------------------
 
-See :ref:`topics-leaks`.
+See :ref:`optimize-memory` and :ref:`topics-leaks`.
 
 Also, Python has a builtin memory leak issue which is described in
 :ref:`topics-leaks-without-leaks`.
@@ -133,7 +128,7 @@ Also, Python has a builtin memory leak issue which is described in
 How can I make Scrapy consume less memory?
 ------------------------------------------
 
-See previous question.
+See the previous question.
 
 How can I prevent memory errors due to many allowed domains?
 ------------------------------------------------------------

scrapy/squeues.py

@@ -167,10 +167,30 @@ _MarshalLifoSerializationDiskQueue = _serializable_queue(
     marshal.loads,
 )
 
-# public queue classes
+# Public queue classes
+
+#: FIFO_ disk queue that serializes :ref:`requests <request>` using
+#: :mod:`pickle`.
+#:
+#: .. _FIFO: https://en.wikipedia.org/wiki/FIFO_(computing_and_electronics)
 PickleFifoDiskQueue = _scrapy_serialization_queue(_PickleFifoSerializationDiskQueue)
+
+#: LIFO_ disk queue that serializes :ref:`requests <request>` using
+#: :mod:`pickle`.
+#:
+#: .. _LIFO: https://en.wikipedia.org/wiki/LIFO_(computing)
 PickleLifoDiskQueue = _scrapy_serialization_queue(_PickleLifoSerializationDiskQueue)
+
+#: FIFO_ disk queue that serializes :ref:`requests <request>` using
+#: :mod:`marshal`.
 MarshalFifoDiskQueue = _scrapy_serialization_queue(_MarshalFifoSerializationDiskQueue)
+
+#: LIFO_ disk queue that serializes :ref:`requests <request>` using
+#: :mod:`marshal`.
 MarshalLifoDiskQueue = _scrapy_serialization_queue(_MarshalLifoSerializationDiskQueue)
+
+#: FIFO_ memory queue.
 FifoMemoryQueue = _scrapy_non_serialization_queue(queue.FifoMemoryQueue)  # type: ignore[arg-type]
+
+#: LIFO_ memory queue.
 LifoMemoryQueue = _scrapy_non_serialization_queue(queue.LifoMemoryQueue)  # type: ignore[arg-type]