lpcm

Large Persistent Cached Map: a dictionary-like Django interface for AWS DynamoDB and memcached

lpcm allows you to have a dictionary-like object in python that automatically interfaces DynamoDB and memcached:

  some_dict = LPCM('some_dict')
  some_dict['pi'] = 3.1415

This will save a key-value pair pi: 3.1415 in both memcached and DynamoDB associated with the map name some_dict. Similarly, you can access the stored values like a regular dictionary:

  some_dict = LPCM('some_dict')
  try:
    v = some_dict['pi']
  except KeyError:
    print "The pi is a lie"

This will first look for the key pi associated with the map name some_dict in memcached. If no associated value is found in memcached, a query is sent to DynamoDB. If DynamoDB returns a value, it will be cached in memcached and then returned, otherwise a KeyError exception is raised.

Atomic increments are also supported:

  user_count = LPCM('user_count')
  user_count.increment(request.user.id)

as are key iterators:

  user_count = LPCM('user_count')
  for user_id in user_count:
    do_stuff(user_id)

In addition to the syntactic sugar, lpcm allows you insulate your production data from the data accessed by unittests and general development. It also allows you to get faster and cheaper testing by switching to cached-only testing during development.

A detailed discussion of the motivations and use cases for lpcm is provided here.

Requirements

• Python 2.7+
• Django 1.4+
• pylibmc
• boto

Django is not really required for any of the lpcm core logic and is only used as a convenient framework for accessing memcached and running unit tests. If you require lpcm in a non-django Python project, please contact me and I will help you set it up.

Running the Tests

1. In settings.py, set your AWS credentials for LPCM_DYNAMODB_ACCESS_KEY and LPCM_DYNAMODB_SECRET_ACCESS_KEY.
2. You can either create the DynamoDB table (by default calledlpcm) manually through the AWS console, or run manage.py create_lpcm_table
3. Run the tests: manage.py test lpcm

Adding lpcm to your own projects

Simply copy the lpcm directory (inside project) and add the required fields to your settings module. Remember to also add it to your INSTALLED_APPS.

License

Copyright (c) 2012 Yavar Naddaf http://www.empiricalresults.ca/ Released Under GNU General Public License. www.gnu.org/licenses/gpl-3.0.txt

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

For a copy of the GNU General Public License, please see: http://www.gnu.org/licenses/.