DiskCache: Disk Backed Cache
DiskCache is an Apache2 licensed disk and file backed cache library, written in pure-Python, and compatible with Django.
The cloud-based computing of 2018 puts a premium on memory. Gigabytes of empty space is left on disks as processes vie for memory. Among these processes is Memcached (and sometimes Redis) which is used as a cache. Wouldn’t it be nice to leverage empty disk space for caching?
Django is Python’s most popular web framework and ships with several caching backends. Unfortunately the file-based cache in Django is essentially broken. The culling method is random and large caches repeatedly scan a cache directory which slows linearly with growth. Can you really allow it to take sixty milliseconds to store a key in a cache with a thousand items?
In Python, we can do better. And we can do it in pure-Python!
In [1]: import pylibmc
In [2]: client = pylibmc.Client(['127.0.0.1'], binary=True)
In [3]: client[b'key'] = b'value'
In [4]: %timeit client[b'key']
10000 loops, best of 3: 25.4 µs per loop
In [5]: import diskcache as dc
In [6]: cache = dc.Cache('tmp')
In [7]: cache[b'key'] = b'value'
In [8]: %timeit cache[b'key']
100000 loops, best of 3: 11.8 µs per loop
Note: Micro-benchmarks have their place but are not a substitute for real measurements. DiskCache offers cache benchmarks to defend its performance claims. Micro-optimizations are avoided but your mileage may vary.
DiskCache efficiently makes gigabytes of storage space available for caching. By leveraging rock-solid database libraries and memory-mapped files, cache performance can match and exceed industry-standard solutions. There’s no need for a C compiler or running another process. Performance is a feature and testing has 100% coverage with unit tests and hours of stress.
Features
- Pure-Python
- Fully Documented
- Benchmark comparisons (alternatives, Django cache backends)
- 100% test coverage
- Hours of stress testing
- Performance matters
- Django compatible API
- Thread-safe and process-safe
- Supports multiple eviction policies (LRU and LFU included)
- Keys support “tag” metadata and eviction
- Developed on Python 2.7
- Tested on CPython 2.7, 3.4, 3.5, 3.6 and PyPy
- Tested on Linux, Mac OS X, and Windows
- Tested using Travis CI and AppVeyor CI
Quickstart
Installing DiskCache is simple with pip:
$ pip install diskcache
You can access documentation in the interpreter with Python’s built-in help function:
>>> from diskcache import Cache, FanoutCache, DjangoCache
>>> help(Cache)
>>> help(FanoutCache)
>>> help(DjangoCache)
User Guide
For those wanting more details, this part of the documentation describes introduction, benchmarks, development, and API.
Reference and Indices
Apache2 License
A large number of open source projects you find today are GPL Licensed. A project that is released as GPL cannot be used in any commercial product without the product itself also being offered as open source.
The MIT, BSD, ISC, and Apache2 licenses are great alternatives to the GPL that allow your open-source software to be used freely in proprietary, closed-source software.
DiskCache is released under terms of the Apache2 License.
DiskCache License
Copyright 2016-2018 Grant Jenks
Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.