Welcome to Django Horizon’s documentation!

Django Horizon

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Simple database sharding (horizontal partitioning) library for Django applications.



  • Shard (horizontal partitioning) by some ForeignKey field like user account.


To install Django Horizon, run this command in your terminal:

$ pip install django-horizon

This is the preferred method to install Django Horizon, as it will always install the most recent stable release.

If you don’t have pip installed, this Python installation guide can guide you through the process.



Add database router configuration in your settings.py:

Horizontal database groups and a metadata store
    'GROUPS': {
        'group1': {  # The name of database horizontal partitioning group
            'DATABASES': {
                1: {
                    'write': 'member1-primary',
                    'read': ['member1-replica-1', 'member1-replica-2'],  # Pick randomly by router
                2: {
                    'write': 'member2-primary',
                    'read': ['member2-replica'],
                3: {
                    'write': 'a3',  # Used by 'read' too
            'PICKABLES': [2, 3],  # Group member keys to pick new database
    'METADATA_MODEL': 'app.HorizontalMetadata',  # Metadata store for horizontal partition key and there database
Database router

Example models

Horizontal partitioning by user

Metadata store
from horizon.models import AbstractHorizontalMetadata

class HorizontalMetadata(AbstractHorizontalMetadata):

In the example, metadata store save followings.

  • group: Group name for horizontal partitioning.
  • key: Determines the distribution of the table’s records among the horizontal partitioning group.
  • index: Choosed database index in horizontal partitioning groups.
Sharded model
from django.conf import settings

from horizon.manager import HorizontalManager  # For Django<1.10
from horizon.models import AbstractHorizontalModel

class SomeLargeModel(AbstractHorizontalModel):
    user = models.ForeignKey(
        db_constraint=False,  # May be using anothor database

    objects = HorizontalManager()  # For Django<1.10

    class Meta(object):
        horizontal_group = 'group1'  # Group name
        horizontal_key = 'user'  # Field name to use group key

In many cases use UUIDField field for id. The AbstractHorizontalModel uses UUIDField as a them id field in default.

Using a model
from django.contrib.auth import get_user_model

user_model = get_user_model()
user = user_model.objects.get(pk=1)

# Get by foreign instance

# Get by foreign id
Model limitations
  • django.db.utils.IntegrityError occured when not specify horizontal key field to filter

  • Cannot lookup by foreign key field, cause there are other (like default) database


Indices and tables