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A set of useful tools that enhance the standard Django cache experience

Project description

Calm Cache for Django

django-calm-cache keeps your cache calm while your site is being hammered by bucket loads of traffic.

this project is forked from pitcrews:django-calm-cache.
Thanks for all the contributors.
But the origin project can't be used in new verion of django.
And it seems the author didn't update the package in pypi.
So I forked and update the django3-calm-cache repository

Key Features

  • Mint caching to avoid the dog pile effect
  • Timeout jitter to reduce the number of entries expiring simultaneously
  • Works alongside any other Django cache backend
  • MemcachedCache and PyLibMCCache Django backends are extended to support data compression provided by python-memcached and pylibmc respectively
  • PyLibMCCache is extended to support binary protocol
  • cache_response decorator that could be applied to any Django view and conditionally cache responses just like Django standard CacheMiddleware and cache_page do, but more configurable, explicit and extensible

Installation

:::shell
pip3 install django3-calm-cache

Cache Backends

Update the cache settings in your settings.py:

:::python
CACHES = {
    'default': {
        'BACKEND' : 'calm_cache.backends.CalmCache',
        'LOCATION': 'locmem-cache',
        'KEY_FUNCTION': 'calm_cache.contrib.sha1_key_func',
        'OPTIONS': {
            'MINT_PERIOD': '10', # Allow stale results for this many seconds. Default: 0 (Off)
            'GRACE_PERIOD': '120', # Serve stale value once during this period. Default: 0 (Off)
            'JITTER': '10', # Upper bound on the random jitter in seconds. Default: 0 (Off)
        },
    },
    'locmem-cache': {
        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        'LOCATION': 'foo',
    },
    'zipped-memcached': {
        'BACKEND': 'calm_cache.backends.MemcachedCache',
        'LOCATION': '127.0.0.1:11211',
        'OPTIONS': {
            'MIN_COMPRESS_LEN': 1024, # Compress values of this size or larger, bytes. Default: 0 (Disabled)
        },
    },
    'zipped-bin-pylibmc': {
        'BACKEND': 'calm_cache.backends.PyLibMCCache',
        'LOCATION': '127.0.0.1:11211',
        'OPTIONS': {
            'MIN_COMPRESS_LEN': 1024, # Compress values of this size or larger, bytes. Default: 0 (Disabled)
            'BINARY': True, # Enable binary protocol for this backend. Default: False (Disabled)
        },
    },
}

Now relax knowing your site's caching won't fall over at the first sign of sustained traffic.

CalmCache Configuration

LOCATION parameter defines the name of another, "real", Django cache backend which will be used to actually store values

CalmCache backend accepts the following options:

  • MINT_PERIOD: the time period that starts right after the user-supplied or default timeout (TIMEOUT setting) ends. First request during this period receives get() miss (None or default) and refreshes the value while all other requests are returning cached (stale) value until it is either updated or expired. Seconds. Default: 0
  • GRACE_PERIOD: the time period starting after mint delay. During grace period stale value is returned only once and is removed after that. Seconds. Default: 0
  • JITTER: defines the range for [0 ... JITTER] random value that is added to client supplied and "real" cache timeouts. Seconds. Default: 0

CalmCache Guidelines

Actual stored key names are composed of CalmCache.make_key() and underlying cache's make_key() methods' outputs, and therefore are stacked:

real_cache_prefix:calm_cache_prefix:user_supplied_key

Minting is designed to cope with highly concurrent requests and good value of MINT_PERIOD would be comparable to the stored object regeneration time.

Grace period starts after mint delay and first request that comes during this time is satisfied with stale value. The value cached under the given key is invalidated immediately and next requesting client will refresh and store a new value. This technique improves hit ratio for infrequently accessed data when occasional staleness is affordable.

Add random variability to the expiry of cache objects as they may be generated at the same time, which mitigates expiry synchronisation

The maximum real cache TTL is caclulated as

timeout + MINT_PERIOD + GRACE_PERIOD + JITTER

Setting MINT_PERIOD, GRACE_PERIOD or JITTER to 0 or not setting them at all turns off relevant logic in the code.

CalmCache Limitations

  • CalmCache currently only supports cache methods add, set, get, delete, has_key and clear

Response Cache

Example usage:

:::python
from calm_cache.decorators import cache_response

@cache_response(15, key_prefix='my_view', codes=(200, 404))
def my_view(request, slug=None):
    return HttpResponse()

cache_response's constructor arguments, relevant Django settings and defaults:

  • cache_timeout: integer, default TTL for cached entries. Required
  • cache: Django cache backend name. If not specified, default cache backend will be used
  • key_prefix: this string is always prepending resulting keys. Default: ''. Django setting: CCRC_KEY_PREFIX
  • methods: a list/tuple with request methods that could be cached. Default: ('GET', ). Django setting: CCRC_CACHE_REQ_METHDODS
  • codes: a list/tuple with cacheable response codes. Default: (200, ). Django setting: CCRC_CACHE_RSP_CODES
  • nocache_req: a dictionary with request headers as keys and regular expressions as values (strings or compiled), so that when request has a header with value matching the expression, the response is never cached. The headers should be put in WSGI format, i.e. 'HTTP_X_FORWARDED_FOR'. Default: {}.
  • nocache_rsp: a list of response headers that prevents response from being cached. Default: ('Set-Cookie', 'Vary'). Django setting: CCRC_NOCACHE_RSP_HEADERS
  • anonymous_only: boolean selecting whether only anonymous requests should be served from the cache/responses cached. Default: True. Django setting: CCRC_ANONYMOUS_REQ_ONLY
  • cache_cookies: boolean, if False, requests with cookies will not be cached, otherwise cookies are ignored. Default: False. Django setting: CCRC_CACHE_REQ_COOKIES
  • excluded_cookies: if cache_cookies is False, cookies found in this list are ignored (considered as not set). If cache_cookies is True, response will not be cached if one of cookies listed is found in the request. Default: (). Django setting: CCRC_EXCLUDED_REQ_COOKIES
  • include_scheme: boolean selecting whether request scheme (http or https) should be used for the key. Default: True. Django setting: CCRC_KEY_SCHEME
  • include_host: boolean selecting whether requested Host: should be used for the key. Default: True. Django setting: CCRC_KEY_HOST
  • hitmiss_header: a tuple with three elements: header name, value for cache hit and another for cache miss. If set to None, the header is never added Default: ('X-Cache', 'Hit', 'Miss')'. Django setting: CCRC_HITMISS_HEADER
  • key_function: optional callable that should be used instead of built-in key function. Has to accept request as its only argument and return either a string with the key or None if the request should not be cached.

ResponseCache Features and Guidelines

  • Unlike CacheMiddleware, cache_response does not analyse Cache-Control header and does not change cache TTL. The header is cached along with the response just like any other header
  • Default settings for cache_reponse are chosen to be the safest, but in order to achieve better cache performance careful configuretion is required
  • By default, reponses with Set-Cookie and Vary headers are never cached, requests that have Cookie header are not cached either
  • Responses that have CSRF token(s) are never cached
  • Requests that have authenticated user associated with them are not cached by default
  • URL and Hostname are used to build the cache key, which could be a problem for certain caching engines due to their limitation to key characters and length. You are advised to use some hashing KEY_FUNCTION in your caching backend, like, for example, provided calm_cache.contrib.sha1_key_func

Legals

License: BSD 3-clause

Copyright (c) 2014, Fairfax Media Limited All rights reserved.

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