Get list of Cache Keys in Django

Question

I'm trying to understand how Django is setting keys for my views. I'm wondering if there's a way to just get all the saved keys from Memcached. something like a cache.all() or something. I've been trying to find the key with cache.has_key('test') but still can't figure out how the view keys are being named.

UPDATE: The reason I need this is because I need to manually delete parts of the cache but dont know the key values Django is setting for my cache_view key

Tacho

Could you clarify why you need this? As my answer below mentions, this isn't possible inside of Django. If we know your use-case, we might be able to provide alternate solutions. – Lavoisier

Does this answer your question? How do I check the content of a Django cache with Python memcached? – Paratyphoid

Related question: How do I delete a cached template fragment in Django? – Luhe

Answer 1

You can use http://www.darkcoding.net/software/memcached-list-all-keys/ as explained in How do I check the content of a Django cache with Python memcached?

Omphalos

Answer 2

For RedisCache you can get all available keys with.

from django.core.cache import cache

cache.keys('*')

Absorbefacient

'RedisCache' object has no attribute 'keys' – Zealot

@KaramHaj I think for newer versions you can try to use cache.get('*') – Absorbefacient

@KaramHaj cache.get('*') returns None instead of every keys like cache.keys('*'). Tested on django 3.2.3 and redis 3.5.3 – Isa

This answer does not work for RedisCache that is provided by Django 4+ See my answer below for more details. – Keiko

This answer does not work for RedisCache in Django >= 4: 'RedisCache' object has no attribute 'keys' – Spradling

Answer 3

As mentioned there is no way to get a list of all cache keys within django. If you're using an external cache (e.g. memcached, or database caching) you can inspect the external cache directly.

But if you want to know how to convert a django key to the one used in the backend system, django's make_key() function will do this.

https://docs.djangoproject.com/en/1.8/topics/cache/#cache-key-transformation

>>> from django.core.cache import caches
>>> caches['default'].make_key('test-key')
u':1:test-key'

Paracasein

Answer 4

For debugging, you can temporarily switch to LocMemCache instead of PyMemcacheCache:

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        'LOCATION': 'unique-snowflake',
    }
}

then see this question:

from django.core.cache.backends import locmem
print(locmem._caches)

Paratyphoid

Answer 5

For Redis Backend

I'm going to add this answer because I landed on this SO question searching for exactly the same question but using a different cache backend. Also with REDIS in particular if you are using the same REDIS server for multiple applications you will want to scope your cache keys with the KEY_PREFIX option otherwise you could end up with cache keys from another application.

My answer is for if you have setup KEY_PREFIX in your settings.py and if you are using either redis_cache.RedisCache or django.core.cache.backends.redis.RedisCache

e.g.

 CACHES = {
    "default": {
        "BACKEND": "redis_cache.RedisCache",
        "LOCATION": f"redis://localhost:6379",
        "KEY_PREFIX": "my_prefix",
    },
 }

or

 CACHES = {
    "default": {
        "BACKEND": "django.core.cache.backends.redis.RedisCache",
        "LOCATION": f"redis://localhost:6379",
        "KEY_PREFIX": "my_prefix",
    },
 }

redis_cache.RedisCache

from django.conf import settings
from django.core.cache import cache

cache_keys = cache.get_client(1).keys(
   f"*{settings.CACHES['default']['KEY_PREFIX']}*"
)

django.core.cache.backends.redis.RedisCache

Doing some tests shows that using Django's built in RedisCache may already be scoped but in my case I'm doing it to be explicit. calling .keys("*") will also return keys that belong to celery tasks

from django.conf import settings
from django.core.cache import cache

cache_keys = cache._cache.get_client().keys(
    f"*{settings.CACHES['default']['KEY_PREFIX']}*"
)

Bonus: Deleting all app keys

If you want to clear the cache for your specific app instead of ALL the keys in REDIS you'll want to using the prior technique and then call cache.delete_many(cache_keys) instead of cache.clear() as the Django Docs warns that using cache.clear() will remove ALL keys in your cache, not just the ones that are created by your app.

Keiko

Answer 6

In my setup with Django 3.2 there is a method to get a "raw" client for Redis which you can get the keys from.

from django.core.cache import cache

cache.get_client(1).keys()

Contraction

This is the answer I was looking for. – Keiko

Note this does not work for the RedisCache backend that is provided with Django>=4. See my answer below for more details. – Keiko

Works for django 2.2.12 as well – Meurer

django 3.2 with redis: this answer gives "AttributeError: 'RedisCache' object has no attribute 'get_client'", while "cache.keys('*')" works fine – Uintathere

Answer 7

The Memcached documentation recommends that instead of listing all the cache keys, you run memcached in verbose mode and see everything that gets changed. You should start memcached like this

memcached -vv

and then it will print the keys as they get created/updated/deleted.

Paratyphoid

Answer 8

You can use memcached_stats from: https://github.com/dlrust/python-memcached-stats. This package makes it possible to view the memcached keys from within the python environment.

Greenheart

Answer 9

If this is not too out of date, I have had similar issue, due I have had to iterate over whole cache. I managed it, when I add something to my cache like in following pseudocode:

#create caches key list if not exists
if not my_cache.get("keys"):
    my_cache.set("keys", [])

#add to my cache
my_cache.set(key, value)

#add key to keys
if key not in my_cache.get("keys"):
    keys_list = my_cache.get("keys")
    keys_list.append(key)
    my_cache.set("keys", keys_list)

Shikari

Answer 10

this helps.

Ref:

https://lzone.de/blog/How-to%20Dump%20Keys%20from%20Memcache

https://github.com/dlrust/python-memcached-stats

import re, telnetlib, sys

key_regex = re.compile(r"ITEM (.*) \[(.*); (.*)\]")
slab_regex = re.compile(r'STAT items:(.*):number')

class MemcachedStats:

    def __init__(self, host='localhost', port='11211'):
        self._host = host
        self._port = port
        self._client = None

    @property
    def client(self):
        if self._client is None:
            self._client = telnetlib.Telnet(self._host, self._port)
        return self._client

    def command(self, cmd):
        ' Write a command to telnet and return the response '
        self.client.write("{}\n".format(cmd).encode())
        res = self.client.read_until('END'.encode()).decode()
        return res

    def slab_ids(self):
        ' Return a list of slab ids in use '
        slab_ids =  slab_regex.findall(self.command('stats items'))
        slab_ids = list(set(slab_ids))
        return slab_ids

    def get_keys_on_slab(self, slab_id, limit=1000000):
        cmd = "stats cachedump {} {}".format(slab_id, limit)
        cmd_output = self.command(cmd)
        matches = key_regex.findall(cmd_output)
        keys = set()
        for match_line in matches:
            keys.add(match_line[0])
        return keys

    def get_all_keys(self):
        slab_ids = self.slab_ids()
        all_keys = set()
        for slab_id in slab_ids:
            all_keys.update(self.get_keys_on_slab(slab_id))
        return list(all_keys)


def main():
    m = MemcachedStats()
    print(m.get_all_keys())

if __name__ == '__main__':
    main()

Dameron

Answer 11

You can get all keys with cache._cache.keys() in reverse order for LocMemCache.

For example, you set 4 cache values as shown below:

from django.core.cache import cache

cache.set("first_name", "John")
cache.set("last_name", "Smith", version=2)
cache.set("age", 36, version=3)
cache.set("gender", "Male")

Then, you can get all the keys with cache._cache.keys() in reverse order as shown below. *:1:, :2: or :3: before each key indicates version:

from django.core.cache import cache

print(cache._cache.keys())
# odict_keys([':1:gender', ':3:age', ':2:last_name', ':1:first_name'])

And, you can iterate all the keys as shown below:

from django.core.cache import cache

for key in cache._cache.keys():
    print(key)

Output:

:1:gender
:3:age
:2:last_name
:1:first_name

And, you can iterate all the keys with the versions as shown below:

from django.core.cache import cache

for key in cache._cache.keys():
    new_key = key.split(":", 2)[2]
    version = key.split(":", 2)[1]
    print(new_key, version)

Output:

gender 1
age 3
last_name 2
first_name 1

Lastly, you can iterate all the key's values which match the keys and versions as shown below. *list() is needed for cache._cache.keys() otherwise you get error and specifying a version is needed for cache.delete() otherwise you cannot delete all the cache values and the answer of my question explains the default version of a cache value with LocMemCache:

from django.core.cache import cache

        # `list()` is needed
for key in list(cache._cache.keys()):
    new_key = key.split(":", 2)[2]
    version = key.split(":", 2)[1]
    print(cache.get(new_key, version=version))

Output:

Male
36
Smith
John

Platelet

Answer 12

>>> from django.core.cache import cache
>>> cache.keys("foo_*")
["foo_1", "foo_2"]

A simple search like this will return all matched values. In databases with a large number of keys this isn't suitable method. Instead, you can use the iter_keys function that works like the keys function but uses Redis server side cursors. Calling iter_keys will return a generator that you can then iterate over efficiently.

>>> from django.core.cache import cache
>>> cache.iter_keys("foo_*")
<generator object algo at 0x7ffa9c2713a8>
>>> next(cache.iter_keys("foo_*"))
"foo_1"

https://github.com/jazzband/django-redis#scan--delete-keys-in-bulk

Organism

Answer 13

There are some weird workarounds you can do to get all keys from the command line, but there is no way to do this with memcached inside of Django. See this thread.

Lavoisier