Package: django-autoshard
Django AutoshardADjangolibrary that makes sharding easy, using theConsistent Hashingalgorithm.NotesWriting a general sharding library for all business models is practically impossible, but there are common particularities that apply to most of them.If you are not familiar with sharding, you should first document yourself on what sharding means and how you could apply it to your own business model. You can starthere.This library was written with the following business model in mind.An application usually has a user account that must be different from other user accounts either by using a unique email address, or username, or other information that can be considered unique across the application.Each user account will be sharded using that unique constraint and all data that belongs to that user will live on the same shard that the user account does.You can perhaps customize this business model to fit your own requirements, but the idea of this library was to add sharding to a Django app, with a minimum amount of effort.The sharding algorithm used by this library is inspired byInstagram’s sharding solution, but instead of an auto-increment ID and stored procedures, this library uses a RNG for the local ID part. This probably means that when the stars align, you might get a collision if an insert is made in the same millisecond and the RNG gives you the same number.Installationpipinstalldjango-autoshardAdddjango_autoshardto your INSTALLED_APPS settings like this:INSTALLED_APPS=(...'django_autoshard',)Create a new user model that extends theShardedModeland extend all related models fromShardRelatedModelfromdjango.contrib.auth.modelsimportAbstractUserfromdjango_autoshard.modelsimportShardedModel,ShardRelatedModelfromdjango_autoshard.managersimportShardedManagerclassUser(ShardedModel,AbstractUser):SHARD_KEY='email'objects=ShardedManager()classBook(ShardRelatedModel):user=models.ForeignKey(User)Use this model as the default auth model in yoursettings.pyfile.AUTH_USER_MODEL='<path.to.your.model>.User'Make sure you have set up thesettings.DATABASEScorrectly(any Django supported database back-end will work) and add the following to your settings file. The range() will create the logical shards, so in the example below, range(10) will create 10 logical shards on the NODE “192.168.0.100” using the default database name, user and password:DJANGO_AUTOSHARD={"NODES":[{"HOST":"192.168.0.100",# DB MACHINE 1"RANGE":range(10)},{"HOST":"192.168.0.101",# DB MACHINE 2"RANGE":range(10,20)}# and so on ...]}Runpythonmanage.pycreate_shardsRunpythonmanage.pymigrateRunpythonmanage.pymigrate_shardsRunpythonmanage.pydrop_constraintsCommandsManagement Commands that come with this library:create_shards:this command will create all the logical shards(new databases) on all of the configured shard nodes insettings.DJANGO_AUTOSHARDmigrate_shards:this command will migrate all your application’s models to all of the logical shards created with “create_shards”drop_constraints:this command will drop all the foreign key constraints from the “default” database that have a relation with your “ShardedModel”SettingsThe settings are isolated into a single dict in your settings.py file like so:DJANGO_AUTOSHARD={'EPOCH':'2016-01-01','MAX_SHARDS':1000,'NODES':{...}}EPOCH- defaults to'2016-01-01'. Must be in'%Y-%m-%d'format.MAX_SHARDS- defaults to8192. This should NEVER be changed after initial setup, unless you want to rehash all your sharded data.Caveatsyou will no longer be able to use database joins between your sharded models, but you can still use joins on models that are related to your sharded model(models on the same shard as the user)models that come from third party apps that are related to your sharded model and you don’t have any control over, will need to have their foreign key dropped(usedrop_constraintscommand).instead of usingBook.objects.create(...)you will have to usebook=Book(...)and thenbook.save(). This is because of how Django model managers work.if your business model requires to do searches on shard related models, or other fields of the sharded model besides the configuredSHARD_KEY, for example text based search, you will need to use tools like Elasticsearch, where you will store your text info and the shard id of tha object that this text info belongs to, in a single Elasticsearch document.ShardedModeldoes not supportcount()andall()django.contrib.adminwill not work with sharded modelsTODOAdd replicas supportCreate shard migration scriptCreate a benchmarking scriptAdd more testsChange Log1.2.0 [2016-06-30]Changed the way shards are built, usingsettings.DJANGO_AUTOSHARD[‘NODES’]. See INSTALLATIONadded support for Django 1.7removed support for python 3.3, because it only worked with Django 1.8django_autoshard User model is only created when testing now.1.1.2 [2016-06-27]allowall()andcount()ifusingis passed.1.1 [2016-05-21]fixes management commands for python2 and python3 < 3.5raiseNotImplementedErrorwhen trying to usecount()orall()on aShardedModelUpdate documentation1.0(alpha) [2016-04-02]Initial release.