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332 lines
11 KiB
ReStructuredText
.. _topics-stats:
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================
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Stats Collection
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================
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Overview
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========
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Scrapy provides a convenient service for collecting stats in the form of
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key/values, both globally and per spider. It's called the Stats Collector, and
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it's a singleton which can be imported and used quickly, as illustrated by the
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examples in the :ref:`topics-stats-usecases` section below.
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The stats collection is enabled by default but can be disabled through the
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:setting:`STATS_ENABLED` setting.
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However, the Stats Collector is always available, so you can always import it
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in your module and use its API (to increment or set new stat keys), regardless
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of whether the stats collection is enabled or not. If it's disabled, the API
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will still work but it won't collect anything. This is aimed at simplifying the
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stats collector usage: you should spend no more than one line of code for
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collecting stats in your spider, Scrapy extension, or whatever code you're
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using the Stats Collector from.
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Another feature of the Stats Collector is that it's very efficient (when
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enabled) and extremely efficient (almost unnoticeable) when disabled.
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The Stats Collector keeps one stats table per open spider and one global stats
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table. You can't set or get stats from a closed spider, but the spider-specific
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stats table is automatically opened when the spider is opened, and closed when
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the spider is closed.
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.. _topics-stats-usecases:
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Common Stats Collector uses
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===========================
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Import the stats collector::
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from scrapy.stats import stats
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Set global stat value::
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stats.set_value('hostname', socket.gethostname())
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Increment global stat value::
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stats.inc_value('spiders_crawled')
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Set global stat value only if greater than previous::
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stats.max_value('max_items_scraped', value)
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Set global stat value only if lower than previous::
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stats.min_value('min_free_memory_percent', value)
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Get global stat value::
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>>> stats.get_value('spiders_crawled')
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8
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Get all global stats (ie. not particular to any spider)::
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>>> stats.get_stats()
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{'hostname': 'localhost', 'spiders_crawled': 8}
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Set spider specific stat value (spider stats must be opened first, but this
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task is handled automatically by the Scrapy engine)::
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stats.set_value('start_time', datetime.now(), spider=some_spider)
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Where ``some_spider`` is a :class:`~scrapy.spider.BaseSpider` object.
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Increment spider-specific stat value::
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stats.inc_value('pages_crawled', spider=some_spider)
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Set spider-specific stat value only if greater than previous::
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stats.max_value('max_items_scraped', value, spider=some_spider)
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Set spider-specific stat value only if lower than previous::
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stats.min_value('min_free_memory_percent', value, spider=some_spider)
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Get spider-specific stat value::
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>>> stats.get_value('pages_crawled', spider=some_spider)
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1238
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Get all stats from a given spider::
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>>> stats.get_stats('pages_crawled', spider=some_spider)
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{'pages_crawled': 1238, 'start_time': datetime.datetime(2009, 7, 14, 21, 47, 28, 977139)}
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.. _topics-stats-ref:
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Stats Collector API
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===================
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There are several Stats Collectors available under the
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:mod:`scrapy.stats.collector` module and they all implement the Stats
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Collector API defined by the :class:`~scrapy.stats.collector.StatsCollector`
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class (which they all inherit from).
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.. module:: scrapy.stats.collector
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:synopsis: Basic Stats Collectors
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.. class:: StatsCollector
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.. method:: get_value(key, default=None, spider=None)
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Return the value for the given stats key or default if it doesn't exist.
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If spider is ``None`` the global stats table is consulted, otherwise the
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spider specific one is. If the spider is not yet opened a ``KeyError``
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exception is raised.
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.. method:: get_stats(spider=None)
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Get all stats from the given spider (if spider is given) or all global
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stats otherwise, as a dict. If spider is not opened ``KeyError`` is
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raied.
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.. method:: set_value(key, value, spider=None)
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Set the given value for the given stats key on the global stats (if
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spider is not given) or the spider-specific stats (if spider is given),
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which must be opened or a ``KeyError`` will be raised.
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.. method:: set_stats(stats, spider=None)
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Set the given stats (as a dict) for the given spider. If the spider is
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not opened a ``KeyError`` will be raised.
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.. method:: inc_value(key, count=1, start=0, spider=None)
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Increment the value of the given stats key, by the given count,
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assuming the start value given (when it's not set). If spider is not
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given the global stats table is used, otherwise the spider-specific
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stats table is used, which must be opened or a ``KeyError`` will be
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raised.
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.. method:: max_value(key, value, spider=None)
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Set the given value for the given key only if current value for the
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same key is lower than value. If there is no current value for the
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given key, the value is always set. If spider is not given the global
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stats table is used, otherwise the spider-specific stats table is used,
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which must be opened or a KeyError will be raised.
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.. method:: min_value(key, value, spider=None)
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Set the given value for the given key only if current value for the
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same key is greater than value. If there is no current value for the
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given key, the value is always set. If spider is not given the global
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stats table is used, otherwise the spider-specific stats table is used,
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which must be opened or a KeyError will be raised.
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.. method:: clear_stats(spider=None)
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Clear all global stats (if spider is not given) or all spider-specific
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stats if spider is given, in which case it must be opened or a
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``KeyError`` will be raised.
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.. method:: iter_spider_stats()
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Return a iterator over ``(spider, spider_stats)`` for each open spider
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currently tracked by the stats collector, where ``spider_stats`` is the
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dict containing all spider-specific stats.
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Global stats are not included in the iterator. If you want to get
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those, use :meth:`get_stats` method.
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.. method:: open_spider(spider)
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Open the given spider for stats collection. This method must be called
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prior to working with any stats specific to that spider, but this task
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is handled automatically by the Scrapy engine.
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.. method:: close_spider(spider)
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Close the given spider. After this is called, no more specific stats
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for this spider can be accessed. This method is called automatically on
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the :signal:`spider_closed` signal.
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Available Stats Collectors
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==========================
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Besides the basic :class:`StatsCollector` there are other Stats Collectors
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available in Scrapy which extend the basic Stats Collector. You can select
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which Stats Collector to use through the :setting:`STATS_CLASS` setting. The
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default Stats Collector is the :class:`MemoryStatsCollector` is used.
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When stats are disabled (through the :setting:`STATS_ENABLED` setting) the
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:setting:`STATS_CLASS` setting is ignored and the :class:`DummyStatsCollector`
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is used.
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MemoryStatsCollector
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--------------------
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.. class:: MemoryStatsCollector
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A simple stats collector that keeps the stats of the last scraping run (for
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each spider) in memory, after they're closed. The stats can be accessed
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through the :attr:`domain_stats` attribute, which is a dict keyed by spider
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domain name.
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This is the default Stats Collector used in Scrapy.
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.. attribute:: domain_stats
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A dict of dicts (keyed by spider domain name) containing the stats of
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the last scraping run for each domain.
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DummyStatsCollector
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-------------------
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.. class:: DummyStatsCollector
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A Stats collector which does nothing but is very efficient. This is the
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Stats Collector used when stats are diabled (through the
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:setting:`STATS_ENABLED` setting).
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SimpledbStatsCollector
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----------------------
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.. module:: scrapy.stats.collector.simpledb
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:synopsis: Simpledb Stats Collector
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.. class:: SimpledbStatsCollector
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A Stats collector which persists stats to `Amazon SimpleDB`_, using one
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SimpleDB item per scraping run (ie. it keeps history of all scraping runs).
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The data is persisted to the SimpleDB domain specified by the
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:setting:`STATS_SDB_DOMAIN` setting. The domain will be created if it
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doesn't exist.
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In addition to the existing stats keys the following keys are added at
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persitance time:
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* ``domain``: the spider domain (so you can use it later for querying stats
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for that domain)
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* ``timestamp``: the timestamp when the stats were persisited
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Both the ``domain`` and ``timestamp`` are used for generating the SimpleDB
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item name in order to avoid overwriting stats of previous scraping runs.
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As `required by SimpleDB`_, datetime's are stored in ISO 8601 format and
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numbers are zero-padded to 16 digits. Negative numbers are not currently
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supported.
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This Stats Collector requires the `boto`_ library.
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.. _Amazon SimpleDB: http://aws.amazon.com/simpledb/
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.. _required by SimpleDB: http://docs.amazonwebservices.com/AmazonSimpleDB/2009-04-15/DeveloperGuide/ZeroPadding.html
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.. _boto: http://code.google.com/p/boto/
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This Stats Collector can be configured through the following settings:
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.. setting:: STATS_SDB_DOMAIN
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STATS_SDB_DOMAIN
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~~~~~~~~~~~~~~~~
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Default: ``'scrapy_stats'``
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A string containing the SimpleDB domain to use in the
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:class:`SimpledbStatsCollector`.
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.. setting:: STATS_SDB_ASYNC
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STATS_SDB_ASYNC
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~~~~~~~~~~~~~~~
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Default: ``False``
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If ``True`` communication with SimpleDB will be performed asynchronously. If
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``False`` blocking IO will be used instead. This is the default as using
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asynchronous communication can result in the stats not being persisted if the
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Scrapy engine is shut down in the middle (for example, when you run only one
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spider in a process and then exit).
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Stats signals
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=============
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The Stats Collector provides some signals for extending the stats collection
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functionality:
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.. module:: scrapy.stats.signals
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:synopsis: Stats Collector signals
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.. signal:: stats_spider_opened
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.. function:: stats_spider_opened(spider)
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Sent right after the stats spider is opened. You can use this signal to add
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startup stats for spider (example: start time).
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:param spider: the stats spider just opened
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:type spider: str
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.. signal:: stats_spider_closing
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.. function:: stats_spider_closing(spider, reason)
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Sent just before the stats spider is closed. You can use this signal to add
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some closing stats (example: finish time).
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:param spider: the stats spider about to be closed
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:type spider: str
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:param reason: the reason why the spider is being closed. See
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:signal:`spider_closed` signal for more info.
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:type reason: str
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.. signal:: stats_spider_closed
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.. function:: stats_spider_closed(spider, reason, spider_stats)
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Sent right after the stats spider is closed. You can use this signal to
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collect resources, but not to add any more stats as the stats spider has
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already been close (use :signal:`stats_spider_closing` for that instead).
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:param spider: the stats spider just closed
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:type spider: str
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:param reason: the reason why the spider was closed. See
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:signal:`spider_closed` signal for more info.
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:type reason: str
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:param spider_stats: the stats of the spider just closed.
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:type reason: dict
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