Stats Collection¶

Overview¶

Scrapy provides a convenient service for collecting stats in the form of key/values, both globally and per spider. It’s called the Stats Collector, and it’s a singleton which can be imported and used quickly, as illustrated by the examples in the Common Stats Collector uses section below.

The stats collection is enabled by default but can be disabled through the STATS_ENABLED setting.

However, the Stats Collector is always available, so you can always import it in your module and use its API (to increment or set new stat keys), regardless of whether the stats collection is enabled or not. If it’s disabled, the API will still work but it won’t collect anything. This is aimed at simplifying the stats collector usage: you should spend no more than one line of code for collecting stats in your spider, Scrapy extension, or whatever code you’re using the Stats Collector from.

Another feature of the Stats Collector is that it’s very efficient (when enabled) and extremely efficient (almost unnoticeable) when disabled.

The Stats Collector keeps one stats table per open spider and one global stats table. You can’t set or get stats from a closed spider, but the spider-specific stats table is automatically opened when the spider is opened, and closed when the spider is closed.

Common Stats Collector uses¶

Import the stats collector:

from scrapy.stats import stats

Set global stat value:

stats.set_value('hostname', socket.gethostname())

Increment global stat value:

stats.inc_value('spiders_crawled')

Set global stat value only if greater than previous:

stats.max_value('max_items_scraped', value)

Set global stat value only if lower than previous:

stats.min_value('min_free_memory_percent', value)

Get global stat value:

>>> stats.get_value('spiders_crawled')
8

Get all global stats (ie. not particular to any spider):

>>> stats.get_stats()
{'hostname': 'localhost', 'spiders_crawled': 8}

Set spider specific stat value (spider stats must be opened first, but this task is handled automatically by the Scrapy engine):

stats.set_value('start_time', datetime.now(), spider=some_spider)

Where some_spider is a BaseSpider object.

Increment spider-specific stat value:

stats.inc_value('pages_crawled', spider=some_spider)

Set spider-specific stat value only if greater than previous:

stats.max_value('max_items_scraped', value, spider=some_spider)

Set spider-specific stat value only if lower than previous:

stats.min_value('min_free_memory_percent', value, spider=some_spider)

Get spider-specific stat value:

>>> stats.get_value('pages_crawled', spider=some_spider)
1238

Get all stats from a given spider:

>>> stats.get_stats('pages_crawled', spider=some_spider)
{'pages_crawled': 1238, 'start_time': datetime.datetime(2009, 7, 14, 21, 47, 28, 977139)}

Stats Collector API¶

There are several Stats Collectors available under the scrapy.statscol module and they all implement the Stats Collector API defined by the StatsCollector class (which they all inherit from).

class scrapy.statscol.StatsCollector¶

get_value(key, default=None, spider=None)¶: Return the value for the given stats key or default if it doesn’t exist. If spider is None the global stats table is consulted, otherwise the spider specific one is. If the spider is not yet opened a KeyError exception is raised.

get_stats(spider=None)¶: Get all stats from the given spider (if spider is given) or all global stats otherwise, as a dict. If spider is not opened KeyError is raised.

set_value(key, value, spider=None)¶: Set the given value for the given stats key on the global stats (if spider is not given) or the spider-specific stats (if spider is given), which must be opened or a KeyError will be raised.

set_stats(stats, spider=None)¶: Set the given stats (as a dict) for the given spider. If the spider is not opened a KeyError will be raised.

inc_value(key, count=1, start=0, spider=None)¶: Increment the value of the given stats key, by the given count, assuming the start value given (when it’s not set). If spider is not given the global stats table is used, otherwise the spider-specific stats table is used, which must be opened or a KeyError will be raised.

max_value(key, value, spider=None)¶: Set the given value for the given key only if current value for the same key is lower than value. If there is no current value for the given key, the value is always set. If spider is not given, the global stats table is used, otherwise the spider-specific stats table is used, which must be opened or a KeyError will be raised.

min_value(key, value, spider=None)¶: Set the given value for the given key only if current value for the same key is greater than value. If there is no current value for the given key, the value is always set. If spider is not given, the global stats table is used, otherwise the spider-specific stats table is used, which must be opened or a KeyError will be raised.

clear_stats(spider=None)¶: Clear all global stats (if spider is not given) or all spider-specific stats if spider is given, in which case it must be opened or a KeyError will be raised.

iter_spider_stats()¶

Return a iterator over (spider, spider_stats) for each open spider currently tracked by the stats collector, where spider_stats is the dict containing all spider-specific stats.

Global stats are not included in the iterator. If you want to get those, use get_stats() method.

open_spider(spider)¶: Open the given spider for stats collection. This method must be called prior to working with any stats specific to that spider, but this task is handled automatically by the Scrapy engine.

close_spider(spider)¶: Close the given spider. After this is called, no more specific stats for this spider can be accessed. This method is called automatically on the spider_closed signal.

Available Stats Collectors¶

Besides the basic StatsCollector there are other Stats Collectors available in Scrapy which extend the basic Stats Collector. You can select which Stats Collector to use through the STATS_CLASS setting. The default Stats Collector used is the MemoryStatsCollector.

When stats are disabled (through the STATS_ENABLED setting) the STATS_CLASS setting is ignored and the DummyStatsCollector is used.

MemoryStatsCollector¶

class scrapy.statscol.MemoryStatsCollector¶

A simple stats collector that keeps the stats of the last scraping run (for each spider) in memory, after they’re closed. The stats can be accessed through the spider_stats attribute, which is a dict keyed by spider domain name.

This is the default Stats Collector used in Scrapy.

spider_stats¶: A dict of dicts (keyed by spider name) containing the stats of the last scraping run for each spider.

DummyStatsCollector¶

class scrapy.statscol.DummyStatsCollector¶: A Stats collector which does nothing but is very efficient. This is the Stats Collector used when stats are disabled (through the STATS_ENABLED setting).

SimpledbStatsCollector¶

class scrapy.contrib.statscol.SimpledbStatsCollector¶

A Stats collector which persists stats to Amazon SimpleDB, using one SimpleDB item per scraping run (ie. it keeps history of all scraping runs). The data is persisted to the SimpleDB domain specified by the STATS_SDB_DOMAIN setting. The domain will be created if it doesn’t exist.

In addition to the existing stats keys, the following keys are added at persitance time:

spider: the spider name (so you can use it later for querying stats for that spider)

timestamp: the timestamp when the stats were persisted

Both the spider and timestamp are used to generate the SimpleDB item name in order to avoid overwriting stats of previous scraping runs.

As required by SimpleDB, datetimes are stored in ISO 8601 format and numbers are zero-padded to 16 digits. Negative numbers are not currently supported.

This Stats Collector requires the boto library.

This Stats Collector can be configured through the following settings:

STATS_SDB_DOMAIN¶

Default: 'scrapy_stats'

A string containing the SimpleDB domain to use in the SimpledbStatsCollector.

STATS_SDB_ASYNC¶

Default: False

If True, communication with SimpleDB will be performed asynchronously. If False blocking IO will be used instead. This is the default as using asynchronous communication can result in the stats not being persisted if the Scrapy engine is shut down in the middle (for example, when you run only one spider in a process and then exit).

Stats signals¶

The Stats Collector provides some signals for extending the stats collection functionality:

scrapy.signals.stats_spider_opened(spider)¶

Sent right after the stats spider is opened. You can use this signal to add startup stats for the spider (example: start time).

Parameters:	spider (str) – the stats spider just opened

scrapy.signals.stats_spider_closing(spider, reason)¶

Sent just before the stats spider is closed. You can use this signal to add some closing stats (example: finish time).

Parameters:	spider (str) – the stats spider about to be closed reason (str) – the reason why the spider is being closed. See `spider_closed` signal for more info.

scrapy.signals.stats_spider_closed(spider, reason, spider_stats)¶

Sent right after the stats spider is closed. You can use this signal to collect resources, but not to add any more stats as the stats spider has already been closed (use stats_spider_closing for that instead).

Parameters:	spider (str) – the stats spider just closed reason (dict) – the reason why the spider was closed. See `spider_closed` signal for more info. spider_stats – the stats of the spider just closed.