Question

What’s the fast method to compress Python objects (list, dictionary, string, etc) before saving them to cache and decompress after read from cache?

I’m using Django and I hope to add compress/decompress support directly in Django’s cache backend which makes it available to all my Django apps.

I looked into django/core/cache/backends/memcached.py

import cmemcache as memcache

class CacheClass(BaseCache):

    def __init__(self, server, params):
        BaseCache.__init__(self, params)
        self._cache = memcache.Client(server.split(';'))

    def get(self, key, default=None):
        val = self._cache.get(smart_str(key))
        if val is None:
            return default
        return val

    def set(self, key, value, timeout=0):
        self._cache.set(smart_str(key), value, self._get_memcache_timeout(timeout))

Looks like pickle/unpickle is done by cmemcache library. I dont know where to put the compress/decompress code.

Answer 1

I looked further into python-memcache’s source code.

It already supported compressing values by zlib before sending them to memcached.

lv = len(val)
# We should try to compress if min_compress_len > 0 and we could
# import zlib and this string is longer than our min threshold.
if min_compress_len and _supports_compress and lv > min_compress_len:
    comp_val = compress(val)
    # Only retain the result if the compression result is smaller
    # than the original.
    if len(comp_val) < lv:
        flags |= Client._FLAG_COMPRESSED
        val = comp_val

def _set(self, cmd, key, val, time, min_compress_len = 0):

Here is Django’s implemention for the “set” command in its memcache backend:

def set(self, key, value, timeout=0):
    self._cache.set(smart_str(key), value, self._get_memcache_timeout(timeout))

Apparently it does not have “min_compress_len” parameter.