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Throttling

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.. versionadded:: VERSION

Sending too many requests too quickly can overwhelm websites. :ref:`Throttling <basic-throttling>` and :ref:`backoff <backoff>` aim to prevent that.

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Concurrency and delay

Requests are throttled on a per-domain basis by default [1]. This allows efficient crawling of multiple sites simultaneously.

Each domain and subdomain is treated separately: requests to books.toscrape.com and quotes.toscrape.com each have their own throttling limits, as do toscrape.com and books.toscrape.com.

The main throttling :ref:`settings <topics-settings>` are:

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```
.. setting:: CONCURRENT_REQUESTS_PER_DOMAIN
```
:setting:`CONCURRENT_REQUESTS_PER_DOMAIN` (default: 1 (:ref:`fallback <default-settings>`: 8))

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Maximum number of simultaneous requests per domain.

It defines a number of “slots” per domain. Each slot can send 1 request at a time: it sends a request, waits for the response, then sends the next request, and so on.
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```
.. setting:: DOWNLOAD_DELAY
```
:setting:`DOWNLOAD_DELAY` (default: 1 (:ref:`fallback <default-settings>`: 0))

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Minimum seconds between any two requests to the same domain.

Even if you have multiple slots, requests to the same domain cannot be sent more frequently than this delay.

To target a specific number of requests per minute (RPM) per domain, set this to 60 / RPM. For example, DOWNLOAD_DELAY = 1.0 for 60 RPM, or DOWNLOAD_DELAY = 2.0 for 30 RPM.
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```
.. setting:: DOWNLOAD_DELAY_PER_SLOT
```
:setting:`DOWNLOAD_DELAY_PER_SLOT` (default: None)

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Minimum seconds to wait between two consecutive requests sent to the same download slot. Unlike :setting:`DOWNLOAD_DELAY`, which applies per domain (:ref:`throttling scope <throttling-scopes>`), this delay is per slot.

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When None (default), the per-slot delay falls back to :setting:`DOWNLOAD_DELAY`, preserving the historical behavior where :setting:`DOWNLOAD_DELAY` was enforced per slot.

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The wait time is measured from when the previous request was sent.

For example, with CONCURRENT_REQUESTS_PER_DOMAIN = 2, DOWNLOAD_DELAY = 0.3, and DOWNLOAD_DELAY_PER_SLOT = 1.0, sending 3 requests to the same domain would result in:

T=0.0s: Request 1 sent (slot 1)
T=0.3s: Request 2 sent (slot 2, respects same-domain delay)
T=0.6s: Request 3 must wait (same-domain delay satisfied, but slot 1 needs 1.0s)
T=1.0s: Request 3 sent (slot 1 can now be reused)

When configuring these settings, note that:

:setting:`CONCURRENT_REQUESTS` caps CONCURRENT_REQUESTS_PER_DOMAIN.

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If DOWNLOAD_DELAY ≥ response time, concurrency is effectively 1. This happens because all slots must wait for the delay between requests, preventing them from sending requests simultaneously.

[1]

(1, 2)

You can :ref:`customize <throttling-scopes>` how requests are grouped for throttling, but domain-based throttling works well in most cases. For more complex domain grouping strategies, see :ref:`alternative-domain-throttling`.

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.. setting:: THROTTLING_SCOPES

Per-domain throttling

The :setting:`THROTTLING_SCOPES` setting allows you to customize throttling behavior for specific domains [1].

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It is a dict that maps scope names to :class:`~scrapy.throttling.ThrottlingScopeConfig` dicts.

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Its default value allows faster crawling of the testing website using during the :ref:`tutorial <intro-tutorial>` while maintaining conservative defaults for other domains:

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.. code-block:: python

    THROTTLING_SCOPES = {
        "quotes.toscrape.com": {"concurrency": 16, "delay": 0.0},
    }

Additional keys like "jitter" and "backoff" can be used here and are covered later on.

Backoff

When servers respond with rate limiting errors (like HTTP 429) or network timeouts occur, request rate is automatically reduced using exponential backoff.

The key settings are:

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```
.. setting:: BACKOFF_HTTP_CODES
```
:setting:`BACKOFF_HTTP_CODES` (default: [429, 502, 503, 504, 520, 521, 522, 523, 524])

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HTTP response status codes that trigger backoff.
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```
.. setting:: BACKOFF_DELAY_FACTOR
```
:setting:`BACKOFF_DELAY_FACTOR` (default: 2.0)

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Factor by which the delay of a scope is multiplied on each backoff step (2×, 4×, 8×, etc.).
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```
.. setting:: BACKOFF_MAX_DELAY
```
:setting:`BACKOFF_MAX_DELAY` (default: 300.0)

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Maximum delay, in seconds, that backoff can reach. Also caps :ref:`Retry-After <retry-after>` and :ref:`RateLimit-Reset <rate-limiting-headers>` delays.

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See :ref:`throttling-settings` for :setting:`BACKOFF_EXCEPTIONS`, :setting:`BACKOFF_JITTER`, :setting:`BACKOFF_MIN_DELAY` and :setting:`BACKOFF_WINDOW`.

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How backoff works

Every :ref:`throttling scope <throttling-scopes>` keeps a current delay that starts at its configured value (0 by default, or :setting:`DOWNLOAD_DELAY` for the default per-domain scopes).

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A backoff trigger is a response whose status code is in :setting:`BACKOFF_HTTP_CODES` or a download exception whose type is in :setting:`BACKOFF_EXCEPTIONS`. On each trigger:

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If the response carries a :ref:`Retry-After or RateLimit-Reset <rate-limiting-headers>` value, that value (capped at :setting:`BACKOFF_MAX_DELAY`) is honored as a hard minimum: no request is sent for the scope until it elapses.

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Otherwise the delay grows exponentially:
```
delay = min(BACKOFF_MAX_DELAY, max(BACKOFF_MIN_DELAY, delay * BACKOFF_DELAY_FACTOR))
```
:setting:`BACKOFF_JITTER` is then applied so that requests that backed off together do not retry in lockstep.

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Recovery is linear: after a scope goes a full :setting:`BACKOFF_WINDOW` without a new trigger, its delay drops by one :setting:`BACKOFF_DELAY_FACTOR` step toward the configured value, and keeps dropping one step per quiet window until it is back to the configured value. A new trigger resets the countdown.

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This exponential-increase / linear-decrease pattern, similar to TCP congestion control, makes a scope back off quickly when a server is unhappy and return to full speed gradually once it recovers. To keep a scope hovering around a target rate instead of repeatedly probing and backing off, enable :ref:`rampup <rampup>`.

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Per-scope backoff configuration

The global BACKOFF_* settings can be overridden per scope with the "backoff" key of a :setting:`THROTTLING_SCOPES` entry, an instance of :class:`~scrapy.throttling.BackoffConfig`:

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.. code-block:: python
    :caption: ``settings.py``

    THROTTLING_SCOPES = {
        "example.com": {
            "backoff": {
                "http_codes": [429, 503],
                "exceptions": ["builtins.IOError"],
                "delay_factor": 1.2,
                "max_delay": 180.0,
                "min_delay": 5.0,
                "jitter": [0.01, 0.33],
            },
        },
    }

Any key left out falls back to the matching global BACKOFF_* setting.

Rampup

When using APIs that charge per request, like web scraping APIs, you often want to maximize throughput while staying within rate limits. To do that, set "rampup" to True in :setting:`THROTTLING_SCOPES`:

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.. code-block:: python
    :caption: ``settings.py``

    THROTTLING_SCOPES = {
        "api.toscrape.com": {
            "rampup": True,
        },
    }

Rampup increases concurrency or lowers delay as needed based on the following setting:

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```
.. setting:: RAMPUP_BACKOFF_TARGET
```
:setting:`RAMPUP_BACKOFF_TARGET` (default: 1)

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Target number of backoff responses per :setting:`BACKOFF_WINDOW` that :ref:`rampup <rampup>` aims for when probing the rate limit of a scope. Can be a range like [1, 3].

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For every :setting:`BACKOFF_WINDOW` that stays below :setting:`RAMPUP_BACKOFF_TARGET` backoff triggers, rampup increases throughput one step: it first lowers the delay, and once the delay reaches its minimum it raises the concurrency limit above the "min_concurrency" floor of the scope. Windows that hit the target hold the current rate, and windows that exceed it let normal :ref:`backoff <backoff>` reduce the rate. The result is a rate that converges on roughly :setting:`RAMPUP_BACKOFF_TARGET` rate-limit responses per window — the most throughput a scope allows without being penalized.

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Rampup behavior can be fine-tuned per scope by giving "rampup" a dict instead of True:

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.. code-block:: python
    :caption: ``settings.py``

    THROTTLING_SCOPES = {
        "api.toscrape.com": {
            "rampup": {
                "backoff_target": [1, 3],  # overrides RAMPUP_BACKOFF_TARGET
                "delay_factor": 0.5,  # multiply the delay by this on each ramp-up step
                "min_delay": 0.05,  # do not ramp the delay below this
            },
        },
    }

Rate limiting headers

Servers may include Retry-After or RateLimit-Reset headers to indicate when you should make your next request. These headers are respected automatically during :ref:`backoff <backoff>`, using their values as minimum delays (capped at :setting:`BACKOFF_MAX_DELAY`).

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.. seealso:: :setting:`REDIRECT_MAX_DELAY`

robots.txt

Crawl-Delay is a non-standard robots.txt directive that indicates a number of seconds to wait between requests.

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.. setting:: THROTTLING_ROBOTSTXT_OBEY

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.. setting:: THROTTLING_ROBOTSTXT_MAX_DELAY

If :setting:`ROBOTSTXT_OBEY` and :setting:`THROTTLING_ROBOTSTXT_OBEY` are True (default), valid Crawl-Delay directives override :setting:`CONCURRENT_REQUESTS_PER_DOMAIN` and :setting:`DOWNLOAD_DELAY`. Concurrency is set to 1 and delay is set to the value of Crawl-Delay, capped at :setting:`THROTTLING_ROBOTSTXT_MAX_DELAY` (default: 60.0).

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If :setting:`THROTTLING_SCOPES` defines a different concurrency or delay, it will be respected, but a warning will be logged about the discrepancy with Crawl-Delay. Set ignore_robots_txt to True to silence this warning.

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Per-request throttling

Sometimes you need different throttling behavior for individual requests or for request groups that are not tied to a specific domain.

For example, you might want to throttle API endpoints differently than web pages on the same domain, group requests by content type (images vs HTML), or apply different throttling based on request priority.

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.. reqmeta:: throttling_scopes

Use the throttling_scopes request metadata to assign requests to custom throttling groups:

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.. code-block:: python

    Request("https://api.example/", meta={"throttling_scopes": "api"})

You can also assign multiple throttling groups to a single request:

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.. code-block:: python

    Request("https://api.example/users", meta={"throttling_scopes": {"api", "users"}})

You can then use the :setting:`THROTTLING_SCOPES` setting to customize throttling for such requests:

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.. code-block:: python
    :caption: ``settings.py``

    THROTTLING_SCOPES = {
        "api": {"concurrency": 2},
        "users": {"delay": 5.0},
    }

Note

These custom throttling groups persist through redirects. For redirect-aware throttling assignment, see :ref:`custom-throttling-scopes`.

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.. reqmeta:: throttling_delay

Delaying a single request

To hold a single request for a fixed number of seconds before it is sent, regardless of its scopes, set the throttling_delay request metadata key:

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.. code-block:: python

    Request("https://example.com/slow", meta={"throttling_delay": 5.0})

The delay is applied once, the first time the request reaches the throttling gate.

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.. reqmeta:: throttling_dont_track

Excluding a request from throttling state

Some requests (authentication flows, one-off API calls, file downloads) should not influence throttling state even if they get a :setting:`BACKOFF_HTTP_CODES` response or raise a :setting:`BACKOFF_EXCEPTIONS` exception. Set the throttling_dont_track request metadata key to True to process such a request normally without letting its outcome trigger :ref:`backoff <backoff>`:

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.. code-block:: python

    Request("https://example.com/login", meta={"throttling_dont_track": True})

Throttling scopes

Throttling scopes represent aspects of requests that can be throttled independently.

Customizing throttling scopes

There are 2 ways to customize throttling scopes.

To configure existing scopes, use the :setting:`THROTTLING_SCOPES` setting. Its keys are scope names and its values are :class:`~scrapy.throttling.ThrottlingScopeConfig` dicts, which accept the following keys:

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concurrency (:class:`int`): System Message: ERROR/3 (<stdin>, line 419); backlink
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Maximum number of concurrent requests for the scope. When unset, the per-domain concurrency (:setting:`CONCURRENT_REQUESTS_PER_DOMAIN`) applies instead.

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min_concurrency (:class:`int`): System Message: ERROR/3 (<stdin>, line 423); backlink
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Concurrency floor that :ref:`backoff <backoff>` and :ref:`rampup <rampup>` never drop below. Defaults to 1.

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delay (:class:`float`): System Message: ERROR/3 (<stdin>, line 427); backlink
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Minimum seconds between requests for the scope. Defaults to :setting:`DOWNLOAD_DELAY`.

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jitter (:class:`float` or 2-:class:`list`): System Message: ERROR/3 (<stdin>, line 430); backlink
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Per-scope override of :setting:`RANDOMIZE_DOWNLOAD_DELAY`.

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quota (:class:`float`): System Message: ERROR/3 (<stdin>, line 433); backlink
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Maximum :ref:`quota <throttling-quotas>` consumed per window.

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window (:class:`float`): System Message: ERROR/3 (<stdin>, line 436); backlink
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Quota window in seconds. Defaults to :setting:`THROTTLING_WINDOW`.

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rampup (:class:`bool` or :class:`dict`): System Message: ERROR/3 (<stdin>, line 439); backlink
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Enables :ref:`rampup <rampup>` for the scope.

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backoff (:class:`~scrapy.throttling.BackoffConfig`): System Message: ERROR/3 (<stdin>, line 442); backlink
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Per-scope :ref:`backoff overrides <per-scope-backoff>`.

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manager (:class:`str` or :class:`type`): System Message: ERROR/3 (<stdin>, line 446); backlink
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Import path or class of a :ref:`custom scope manager <custom-throttling-scope-managers>` for the scope.

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ignore_robots_txt (:class:`bool`): System Message: ERROR/3 (<stdin>, line 450); backlink
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Silences the warning logged when this configuration is more aggressive than a :ref:`robots.txt Crawl-delay <crawl-delay>`.

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.. setting:: THROTTLING_MANAGER

To change how scopes are assigned (or anything beyond per-scope settings), set :setting:`THROTTLING_MANAGER` (default: :class:`~scrapy.throttling.ThrottlingManager`) to a :ref:`component <topics-components>` that implements the :class:`~scrapy.throttling.ThrottlingManagerProtocol` protocol (or its import path as a string):

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.. code-block:: python
    :caption: ``settings.py``

    THROTTLING_MANAGER = "myproject.throttling.MyThrottlingManager"

Handling of multiple throttling scopes

When a request has multiple throttling scopes, it is not sent until all of its throttling scopes allow it.

Throttling quotas

When different requests can consume different amounts of a throttling scope, you can express this using throttling quotas.

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.. setting:: THROTTLING_WINDOW

Use the :setting:`THROTTLING_WINDOW` setting (default: 60.0) or the "window" key in the :setting:`THROTTLING_SCOPES` setting to define the time window after which throttling quotas are reset.

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Then use the :setting:`THROTTLING_SCOPES` setting to define the throttling quotas for each throttling scope:

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.. code-block:: python
    :caption: ``settings.py``

    THROTTLING_SCOPES = {
        "api.toscrape.com": {
            "quota": 500.0,
        },
    }

Then, in the :reqmeta:`throttling_scopes` request metadata key or in the return value of the :meth:`~scrapy.throttling.ThrottlingManagerProtocol.get_scopes` method, define a :class:`dict` where keys are throttling scopes and values are :class:`float` values that indicate the expected quota consumption (it does not need to be exact).

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Everything else being equal, :class:`~scrapy.pqueues.ScrapyPriorityQueue` will prioritize requests that consume a higher portion of the available throttling quota, to minimize the risk of those requests getting stuck.

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Customizing throttling scope managers

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.. setting:: THROTTLING_SCOPE_MANAGER

The :setting:`THROTTLING_SCOPE_MANAGER` setting (default: :class:`~scrapy.throttling.ThrottlingScopeManager`) is a :ref:`component <topics-components>` that implements the :class:`~scrapy.throttling.ThrottlingScopeManagerProtocol` (or its import path as a string):

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.. code-block:: python
    :caption: ``settings.py``

    THROTTLING_SCOPE_MANAGER = "myproject.throttling.MyThrottlingScopeManager"

For each throttling scope, an instance of this class is created to manage any gradual :ref:`backoff <backoff>` or :ref:`rampup <rampup>` required at run time.

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You can implement your own throttling scope manager if you wish to change the backoff or rampup behavior beyond what settings allow.

You can also define a custom throttling scope manager for a specific throttling scope by setting the "manager" key in the :setting:`THROTTLING_SCOPES` setting:

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.. code-block:: python
    :caption: ``settings.py``

    THROTTLING_SCOPES = {
        "api.toscrape.com": {
            "manager": "myproject.throttling.MyThrottlingScopeManager",
        },
    }

A scope manager only needs to implement the :class:`~scrapy.throttling.ThrottlingScopeManagerProtocol`. For example, the following manager enforces a fixed quota per time window without any delay or exponential backoff, similar to a fixed-window rate limiter:

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Unknown interpreted text role "class".

System Message: ERROR/3 (<stdin>, line 553)

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.. code-block:: python
    :caption: ``myproject/throttling.py``

    import time


    class FixedWindowScopeManager:
        def __init__(self, crawler, config):
            self.limit = config["quota"]
            self.window = config.get("window", 60.0)
            self.reset_at = None
            self.used = 0.0
            self.active = 0

        @classmethod
        def from_crawler(cls, crawler, config):
            return cls(crawler, config)

        def can_send(self, now=None, amount=None):
            now = now if now is not None else time.monotonic()
            if self.reset_at is not None and now >= self.reset_at:
                self.reset_at, self.used = None, 0.0
            if self.used and self.used + (amount or 0) > self.limit:
                return self.reset_at - now
            return 0.0

        def record_sent(self, now=None, amount=None):
            now = now if now is not None else time.monotonic()
            if self.reset_at is None:
                self.reset_at = now + self.window
            self.used += amount or 0
            self.active += 1

        def record_done(self, now=None):
            self.active = max(0, self.active - 1)

        def record_backoff(self, delay=None, now=None):
            pass  # this manager does not back off

        def reconcile_quota(self, consumed=None, remaining=None, now=None):
            if remaining is not None:
                self.used = max(0.0, self.limit - remaining)
            elif consumed is not None:
                self.used = max(0.0, self.used + consumed)

        def set_base_delay(self, delay):
            pass

        def set_concurrency(self, concurrency):
            pass

        def is_idle(self, now, max_idle):
            return self.active == 0

Throttling-aware scheduling

By default, throttling is enforced at the engine, where a request waiting on its :ref:`throttling scopes <throttling-scopes>` holds a concurrency slot. In a crawl that mixes heavily-throttled scopes with unthrottled ones, this can let throttled requests starve unthrottled ones that could be sent right away (head-of-line blocking; Scrapy logs a warning, see :setting:`DELAYED_REQUESTS_WARN_THRESHOLD`).

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:class:`~scrapy.core.scheduler.ThrottlingAwareScheduler` avoids this. To enable it:

System Message: ERROR/3 (<stdin>, line 619); backlink

Unknown interpreted text role "class".

System Message: ERROR/3 (<stdin>, line 622)

Error in "code-block" directive: unknown option: "caption".

.. code-block:: python
    :caption: ``settings.py``

    SCHEDULER = "scrapy.core.scheduler.ThrottlingAwareScheduler"
    SCHEDULER_PRIORITY_QUEUE = "scrapy.pqueues.ThrottlingAwarePriorityQueue"

System Message: ERROR/3 (<stdin>, line 628)

Unknown directive type "autoclass".

.. autoclass:: scrapy.core.scheduler.ThrottlingAwareScheduler

Examples

Alternative domain throttling

If you are not happy with the :ref:`default throttling scope behavior <basic-throttling>` with regards to domains and subdomains, you can change it.

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Alternative approaches include:

Using the highest-level registrable domain as the throttling scope, e.g. https://books.toscrape.com and https://toscrape.com both get a toscrape.com throttling scope.

This allows to apply the same throttling settings to all subdomains of a registrable domain.

For example:

System Message: ERROR/3 (<stdin>, line 654)

Error in "code-block" directive: unknown option: "caption".

.. code-block:: python
    :caption: ``settings.py``

    import tldextract
    from scrapy.utils.httpobj import urlparse_cached


    class MyThrottlingManager:

        def get_request_scopes(self, request):
            extracted = tldextract.extract(request.url)
            if extracted.domain and extracted.suffix:
                return f"{extracted.domain}.{extracted.suffix}"
            return urlparse_cached(request).netloc


    THROTTLING_MANAGER = MyThrottlingManager

Using multiple throttling scopes per request, one per registrable domain and for every higher-level subdomain, e.g. https://books.toscrape.com and https://toscrape.com both get a toscrape.com throttling scope, but https://books.toscrape.com also gets a books.toscrape.com throttling scope.

This allows to apply the same throttling settings to all subdomains of a registrable domain, but also allows applying further restrictions on each or on some subdomains.

For example:

System Message: ERROR/3 (<stdin>, line 684)

Error in "code-block" directive: unknown option: "caption".

.. code-block:: python
    :caption: ``settings.py``

    import tldextract
    from scrapy.utils.httpobj import urlparse_cached


    class MyThrottlingManager:

        def get_request_scopes(self, request):
            extracted = tldextract.extract(request.url)
            if not (extracted.domain and extracted.suffix):
                return urlparse_cached(request).netloc
            scopes = set()
            registrable_domain = f"{extracted.domain}.{extracted.suffix}"
            scopes.add(registrable_domain)
            if extracted.subdomain:
                subdomain_parts = extracted.subdomain.split(".")
                for i in range(len(subdomain_parts)):
                    subdomain = ".".join(subdomain_parts[i:])
                    full_domain = f"{subdomain}.{registrable_domain}"
                    scopes.add(full_domain)
            return scopes


    THROTTLING_MANAGER = MyThrottlingManager
    THROTTLING_SCOPES = {
        "toscrape.com": {"concurrency": 32},
        "books.toscrape.com": {"concurrency": 24},
        "quotes.toscrape.com": {"concurrency": 16},
    }

Here books.toscrape.com requests can reach 24 concurrency and quotes.toscrape.com requests can reach 16 concurrency, but never both at the same time, because that would sum 40 concurrency, and toscrape.com requests are limited to 32.

Endpoint-specific throttling

To apply different throttling settings to different endpoints of the same domain and not enforce any common throttling, effectively treating them as different domains:

Implement a :ref:`throttling manager <custom-throttling-scopes>` that sets endpoint-specific throttling scopes for that domain:

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.. code-block:: python

    from scrapy.throttling import ThrottlingManager, scope_cache
    from scrapy.utils.httpobj import urlparse_cached


    class MyThrottlingManager(ThrottlingManager):
        @scope_cache
        async def get_scopes(self, request):
            parsed_url = urlparse_cached(request)
            if parsed_url.netloc != "api.toscrape.com":
                return await super().get_scopes(request)
            return f"{parsed_url.netloc}{parsed_url.path}"

Use the :setting:`THROTTLING_SCOPES` setting to set different throttling settings per endpoint:

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```
.. code-block:: python
    :caption: ``settings.py``

    THROTTLING_SCOPES = {
        "api.toscrape.com/fast-endpoint": {"concurrency": 1000, "delay": 0.08},
        "api.toscrape.com/slow-endpoint": {"delay": 5.0},
    }
```

Web scraping API throttling

Imagine you are sending requests to a web scraping API, e.g. to avoid bans. Unless that API provides a Scrapy plugin to make it easier to use, you may want to:

Use the :setting:`THROTTLING_SCOPES` setting to increase concurrency for API requests. For example:

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Unknown interpreted text role "setting".
System Message: ERROR/3 (<stdin>, line 771)

Error in "code-block" directive: unknown option: "caption".
```
.. code-block:: python
    :caption: ``settings.py``

    THROTTLING_SCOPES = {
        "api.toscrape.com": {"concurrency": 1000, "delay": 0.08},
    }
```

Implement a :ref:`throttling manager <custom-throttling-scopes>` that:

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Adds a throttling scope for the URL being scraped.

For example, if you request https://api.toscrape.com/?url=https://example.com, by default it will get a api.toscrape.com throttling scope, but it should also get the example.com throttling scope:

System Message: WARNING/2 (<stdin>, line 787)

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.. code-block:: python

    from urllib.parse import urlparse

    from scrapy.throttling import add_scope, ThrottlingManager, scope_cache
    from scrapy.utils.httpobj import urlparse_cached
    from w3lib.url import url_query_parameter


    class MyThrottlingManager(ThrottlingManager):
        @scope_cache
        async def get_scopes(self, request):
            scopes = await super().get_scopes(request)
            if urlparse_cached(request).netloc != "api.toscrape.com":
                return scopes
            target_url = url_query_parameter(request.url, "url")
            if not target_url:
                return scopes
            target_domain = urlparse(target_url).netloc
            return add_scope(scopes, target_domain)

Can differentiate between exhaustion of the target website and exhaustion of the API itself. For example:

System Message: WARNING/2 (<stdin>, line 811)

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.. code-block:: python

    from scrapy.throttling import ThrottlingManager
    from scrapy.utils.httpobj import urlparse_cached


    class MyThrottlingManager(ThrottlingManager):
        async def get_response_backoff(self, response):
            if (
                urlparse_cached(response.request).netloc != "api.toscrape.com"
                or response.status != 200
            ):
                return await super().get_response_backoff(response)
            upstream_status_code = int(
                response.headers.get("X-Upstream-Status-Code", b"200")
            )
            upstream_response = response.__class__(
                response.url,
                status=upstream_status_code,
                headers=response.headers,
                body=response.body,
            )
            return await super().get_response_backoff(upstream_response)

Cost-capped throttling

Imagine you are using an API that charges different requests differently, e.g. based on the features used, and you want to limit how much you spend per time window (:setting:`BACKOFF_WINDOW`). You can use :ref:`throttling quotas <throttling-quotas>` for that:

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Implement a :ref:`throttling manager <custom-throttling-scopes>` that:

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Sets a cost throttling scope on each request to some estimation based e.g. on request URL parameters:

System Message: WARNING/2 (<stdin>, line 851)

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.. code-block:: python

    from scrapy.utils.httpobj import urlparse_cached
    from scrapy.throttling import ThrottlingManager, scope_cache


    class MyThrottlingManager(ThrottlingManager):
        @scope_cache
        async def get_scopes(self, request):
            scopes = await super().get_scopes(request)
            parsed_url = urlparse_cached(request)
            if parsed_url.netloc != "api.toscrape.com":
                return scopes
            return add_scope(scopes, "cost", estimate_request_cost(request))

Reconciles the estimated cost with the actual cost reported by the response, so that the quota tracks real spending:

System Message: WARNING/2 (<stdin>, line 869)

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.. code-block:: python

    from scrapy.throttling import ThrottlingManager, update_scope_backoff


    class MyThrottlingManager(ThrottlingManager):
        async def get_response_backoff(self, response):
            backoff = await super().get_response_backoff(response)
            if response.headers.get("X-Actual-Cost") is None:
                return backoff
            estimated = estimate_request_cost(response.request)
            actual = float(response.headers[b"X-Actual-Cost"])
            # Report the difference between actual and estimated cost.
            return update_scope_backoff(backoff, "cost", consumed=actual - estimated)

Use the :setting:`THROTTLING_SCOPES` setting to set a maximum cost per time window:

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```
.. code-block:: python
    :caption: ``settings.py``

    THROTTLING_SCOPES = {
        "cost": {"quota": 100.0},
    }
```
This will allow you to spend up to 100.0 units of cost per time window (default: 60 seconds) before throttling kicks in.

Per-IP concurrency limiting

A concurrency limit keyed by IP is just a throttling scope whose id is the request's IP, with a concurrency limit. A request then carries two scopes, its domain and its IP, and is only sent when both allow it (see :ref:`multiple-throttling-scopes`).

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Implement a :ref:`throttling manager <custom-throttling-scopes>` that adds the request's IP as a second scope:

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.. code-block:: python

    import socket

    from scrapy.throttling import ThrottlingManager, add_scope, scope_cache
    from scrapy.utils.asyncio import run_in_thread
    from scrapy.utils.httpobj import urlparse_cached


    class IPThrottlingManager(ThrottlingManager):
        @scope_cache
        async def get_scopes(self, request):
            scopes = await super().get_scopes(request)
            host = urlparse_cached(request).hostname
            address = await run_in_thread(socket.gethostbyname, host)
            return add_scope(scopes, address)

Additional settings

System Message: ERROR/3 (<stdin>, line 931)

Unknown directive type "setting".
```
.. setting:: BACKOFF_EXCEPTIONS
```
:setting:`BACKOFF_EXCEPTIONS`

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Default:
- :exc:`~scrapy.exceptions.DownloadFailedError`
  
  System Message: ERROR/3 (<stdin>, line 937); backlink
  
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- :exc:`~scrapy.exceptions.DownloadTimeoutError`
  
  System Message: ERROR/3 (<stdin>, line 938); backlink
  
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- :exc:`~scrapy.exceptions.ResponseDataLossError`
  
  System Message: ERROR/3 (<stdin>, line 939); backlink
  
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List of exception classes that trigger backoff when raised while downloading a request. Strings are interpreted as import paths.
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```
.. seealso:: :setting:`RETRY_EXCEPTIONS`
```
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```
.. setting:: BACKOFF_JITTER
```
:setting:`BACKOFF_JITTER` (default: 0.1)

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Random jitter applied to each backoff delay, as a fraction of the delay. With the default value of 0.1 the delay is randomized by ±10%. Overrides :setting:`RANDOMIZE_DOWNLOAD_DELAY` during backoff.

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```
.. setting:: BACKOFF_MIN_DELAY
```
:setting:`BACKOFF_MIN_DELAY` (default: 1.0)

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Delay, in seconds, applied on the first backoff step (and the minimum delay during backoff).
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```
.. setting:: BACKOFF_WINDOW
```
:setting:`BACKOFF_WINDOW` (default: 60.0)

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Time window, in seconds, used by :ref:`backoff <backoff>` and :ref:`rampup <rampup>`. During backoff, a :ref:`throttling scope <throttling-scopes>` must go this many seconds without a new backoff trigger (an HTTP error code from :setting:`BACKOFF_HTTP_CODES` or an exception from :setting:`BACKOFF_EXCEPTIONS`) before its delay decreases by one :setting:`BACKOFF_DELAY_FACTOR` step toward the configured value. A new trigger resets the countdown.

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```
.. setting:: DELAYED_REQUESTS_WARN_THRESHOLD
```
:setting:`DELAYED_REQUESTS_WARN_THRESHOLD` (default: 500)

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Number of requests held back by :ref:`throttling <throttling>` at which Scrapy logs a warning, to help detect throttling configurations that hold back more requests than expected.

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While throttled, requests in the :ref:`scheduler <topics-scheduler>` remain in the scheduler. However, requests sent with :meth:`engine.download() <scrapy.core.engine.ExecutionEngine.download>` bypass the scheduler, including requests sent by some built-in :ref:`components <topics-components>` and :ref:`inline requests <inline-requests>`. When such requests are throttled, they are paused and kept in memory, along with any run time context from the code that is sending them. If they accumulate, they can become a memory issue.

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System Message: ERROR/3 (<stdin>, line 990)

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```
.. setting:: RANDOMIZE_DOWNLOAD_DELAY
```
:setting:`RANDOMIZE_DOWNLOAD_DELAY` (default: True)

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Unknown interpreted text role "setting".

Randomize delays by this factor, e.g. if 0.2 randomize delays between delay*0.8 and delay*1.2.

It can be set to a 2-item list with low and high factors, e.g. [-0.1, 0.3] to randomize delays between delay*0.9 and delay*1.3.

If True, 0.5 (i.e. ±50%) is used as the randomization factor. If False, no randomization is applied.
System Message: ERROR/3 (<stdin>, line 1004)

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```
.. setting:: THROTTLING_DEBUG
```
:setting:`THROTTLING_DEBUG` (default: False)

System Message: ERROR/3 (<stdin>, line 1006); backlink

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Whether to log :ref:`throttling <throttling>` decisions (per-scope delays, backoff steps and recoveries) for debugging.

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```
.. setting:: THROTTLING_SCOPE_MAX_IDLE
```
:setting:`THROTTLING_SCOPE_MAX_IDLE` (default: 3600.0)

System Message: ERROR/3 (<stdin>, line 1013); backlink

Unknown interpreted text role "setting".

Seconds of inactivity after which the state of a :ref:`throttling scope <throttling-scopes>` is evicted from memory to bound memory usage on long-running crawls. Set to 0 to never evict. Scopes in active backoff are never evicted.

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Migrating from AutoThrottle

The AutoThrottle extension is deprecated in favor of the throttling and :ref:`backoff <backoff>` system described here, which is always active and does not need to be enabled.

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Setting :setting:`AUTOTHROTTLE_ENABLED` to True still works but logs a deprecation warning. To migrate, drop the AUTOTHROTTLE_* settings and use the following equivalents:

System Message: ERROR/3 (<stdin>, line 1029); backlink

Unknown interpreted text role "setting".

AutoThrottle	Throttling
`AUTOTHROTTLE_ENABLED = True`	No equivalent; throttling is always active.
`AUTOTHROTTLE_START_DELAY`	:setting:`DOWNLOAD_DELAY` System Message: ERROR/3 (`<stdin>`, line 1041); backlink Unknown interpreted text role "setting".
`AUTOTHROTTLE_MAX_DELAY`	:setting:`BACKOFF_MAX_DELAY` System Message: ERROR/3 (`<stdin>`, line 1043); backlink Unknown interpreted text role "setting".
`AUTOTHROTTLE_TARGET_CONCURRENCY`	:ref:`rampup <rampup>` (`"rampup": True`) System Message: ERROR/3 (`<stdin>`, line 1045); backlink Unknown interpreted text role "ref".
`AUTOTHROTTLE_DEBUG = True`	:setting:`THROTTLING_DEBUG` `= True` System Message: ERROR/3 (`<stdin>`, line 1047); backlink Unknown interpreted text role "setting".
`autothrottle_dont_adjust_delay` (request meta)	:reqmeta:`throttling_dont_track` (request meta) System Message: ERROR/3 (`<stdin>`, line 1049); backlink Unknown interpreted text role "reqmeta".

AutoThrottle adjusted the delay of each download slot based on response latency. The new system does not measure latency; instead, it reacts to explicit rate-limit signals (:setting:`BACKOFF_HTTP_CODES`, :setting:`BACKOFF_EXCEPTIONS`, :ref:`Retry-After / RateLimit-Reset <rate-limiting-headers>`) and, with :ref:`rampup <rampup>`, probes for the fastest rate a scope tolerates. If you specifically need latency-based control, implement a custom :ref:`throttling scope manager <custom-throttling-scope-managers>`.

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API

System Message: ERROR/3 (<stdin>, line 1066)

Unknown directive type "autoclass".

.. autoclass:: scrapy.throttling.ThrottlingManagerProtocol
    :members:
    :member-order: bysource

System Message: ERROR/3 (<stdin>, line 1070)

Unknown directive type "autoclass".

.. autoclass:: scrapy.throttling.ThrottlingManager
    :members: get_response_delay

System Message: ERROR/3 (<stdin>, line 1073)

Unknown directive type "autoclass".

.. autoclass:: scrapy.throttling.ThrottlingScopeManagerProtocol
    :members:
    :member-order: bysource

System Message: ERROR/3 (<stdin>, line 1077)

Unknown directive type "autoclass".

.. autoclass:: scrapy.throttling.ThrottlingScopeManager

System Message: ERROR/3 (<stdin>, line 1079)

Unknown directive type "autoclass".

.. autoclass:: scrapy.pqueues.ThrottlingAwarePriorityQueue

System Message: ERROR/3 (<stdin>, line 1081)

Unknown directive type "autoclass".

.. autoclass:: scrapy.throttling.ThrottlingScopeConfig

System Message: ERROR/3 (<stdin>, line 1083)

Unknown directive type "autoclass".

.. autoclass:: scrapy.throttling.BackoffConfig

System Message: ERROR/3 (<stdin>, line 1085)

Unknown directive type "autofunction".

.. autofunction:: scrapy.throttling.scope_cache

System Message: ERROR/3 (<stdin>, line 1086)

Unknown directive type "autofunction".

.. autofunction:: scrapy.throttling.add_scope

System Message: ERROR/3 (<stdin>, line 1087)

Unknown directive type "autofunction".

.. autofunction:: scrapy.throttling.update_scope_backoff

</html>

37 KiB Raw Blame History Unescape Escape

Throttling

Concurrency and delay

Per-domain throttling

Backoff

How backoff works

Per-scope backoff configuration

Rampup

Rate limiting headers

robots.txt

Per-request throttling

Delaying a single request

Excluding a request from throttling state

Throttling scopes

Customizing throttling scopes

Handling of multiple throttling scopes

Throttling quotas

Customizing throttling scope managers

Throttling-aware scheduling

Examples

Alternative domain throttling

Endpoint-specific throttling

Web scraping API throttling

Cost-capped throttling

Per-IP concurrency limiting

Additional settings

Migrating from AutoThrottle

API

37 KiB

Raw Blame History