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Merge pull request #502 from scrapy/doc-fixes 

DOWNLOAD_DELAY docs clarification
This commit is contained in:
Pablo Hoffman 2014-01-14 21:07:42 -08:00
parent 3d308d7732 9a999daa2a
commit ea2f897b81
2 changed files with 16 additions and 5 deletions
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4
docs/topics/autothrottle.rst
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@ -40,7 +40,9 @@ This adjusts download delays and concurrency based on the following rules:
.. note:: The AutoThrottle extension honours the standard Scrapy settings for
concurrency and delay. This means that it will never set a download delay
lower than :setting:`DOWNLOAD_DELAY` or a concurrency higher than :setting:`CONCURRENT_REQUESTS_PER_DOMAIN` (or :setting:`CONCURRENT_REQUESTS_PER_IP`, depending on which one you use).
lower than :setting:`DOWNLOAD_DELAY` or a concurrency higher than
:setting:`CONCURRENT_REQUESTS_PER_DOMAIN`
(or :setting:`CONCURRENT_REQUESTS_PER_IP`, depending on which one you use).
Settings
========

17
docs/topics/settings.rst
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@ -200,6 +200,11 @@ performed to any single IP. If non-zero, the
used instead. In other words, concurrency limits will be applied per IP, not
per domain.
This setting also affects :setting:`DOWNLOAD_DELAY`:
if :setting:`CONCURRENT_REQUESTS_PER_IP` is non-zero, download delay is
enforced per IP, not per domain.
.. setting:: DEFAULT_ITEM_CLASS
DEFAULT_ITEM_CLASS
@ -339,18 +344,22 @@ DOWNLOAD_DELAY
Default: ``0``
The amount of time (in secs) that the downloader should wait before downloading
consecutive pages from the same spider. This can be used to throttle the
consecutive pages from the same website. This can be used to throttle the
crawling speed to avoid hitting servers too hard. Decimal numbers are
supported. Example::
DOWNLOAD_DELAY = 0.25 # 250 ms of delay
DOWNLOAD_DELAY = 0.25 # 250 ms of delay
This setting is also affected by the :setting:`RANDOMIZE_DOWNLOAD_DELAY`
setting (which is enabled by default). By default, Scrapy doesn't wait a fixed
amount of time between requests, but uses a random interval between 0.5 and 1.5
* :setting:`DOWNLOAD_DELAY`.
You can also change this setting per spider.
When :setting:`CONCURRENT_REQUESTS_PER_IP` is non-zero, delays are enforced
per ip address instead of per domain.
You can also change this setting per spider by setting ``download_delay``
spider attribute.
.. setting:: DOWNLOAD_HANDLERS
@ -644,7 +653,7 @@ Default: ``True``
If enabled, Scrapy will wait a random amount of time (between 0.5 and 1.5
* :setting:`DOWNLOAD_DELAY`) while fetching requests from the same
spider.
website.
This randomization decreases the chance of the crawler being detected (and
subsequently blocked) by sites which analyze requests looking for statistically