Warning

Table partitioning is a relatively new and advanded PostgreSQL feature. It has plenty of ways to shoot yourself in the foot with.

We HIGHLY RECOMMEND you only use this feature if you’re already deeply familiar with table partitioning and aware of its advantages and disadvantages.

Do study the PostgreSQL documentation carefuly.

Table partitioning

PostgresPartitionedModel adds support for PostgreSQL Declarative Table Partitioning.

The following partitioning method are available:

  • PARTITION BY RANGE

  • PARTITION BY LIST

Note

Although table partitioning is available in PostgreSQL 10.x, it is highly recommended you use PostgresSQL 11.x. Table partitioning got a major upgrade in PostgreSQL 11.x.

PostgreSQL 10.x does not support creating foreign keys to/from partitioned tables and does not automatically create an index across all partitions.

Creating partitioned tables

Partitioned tables are declared like regular Django models with a special base class and two extra options to set the partitioning method and key. Once declared, they behave like regular Django models.

Declaring the model

Inherit your model from psqlextra.models.PostgresPartitionedModel and declare a child class named PartitioningMeta. On the meta class, specify the partitioning method and key.

from django.db import models

from psqlextra.types import PostgresPartitioningMethod
from psqlextra.models import PostgresPartitionedModel

class MyModel(PostgresPartitionedModel):
    class PartitioningMeta:
        method = PostgresPartitioningMethod.RANGE
        key = ["timestamp"]

    name = models.TextField()
    timestamp = models.DateTimeField()

Generating a migration

Run the following command to automatically generate a migration:

python manage.py pgmakemigrations

This will generate migrationt that creates the partitioned table with a default partition.

Adding/removing partitions manually

Postgres does not have support for automatically creating new partitions as needed. Therefor, one must manually add new partitions. Depending on the partitioning method you have chosen, the partition has to be created differently.

Partitions are tables. Each partition must be given a unique name. PostgresPartitionedModel does not require you to create a model for each partition because you are not supposed to query partitions directly.

Using migrations

Migrations for the creation and deletion of partitioned models can be handled automatically using the special pgmakemigrations command:

python manage.py pgmakemigrations

Adding a range partition

Use the PostgresAddRangePartition operation to add a new range partition. Only use this operation when your partitioned model uses the psqlextra.types.PostgresPartitioningMethod.RANGE.

from django.db import migrations, models

from psqlextra.migrations.operations import PostgresAddRangePartition

class Migration(migrations.Migration):
    operations = [
        PostgresAddRangePartition(
           model_name="mypartitionedmodel",
           name="pt1",
           from_values="2019-01-01",
           to_values="2019-02-01",
        ),
    ]

Adding a list partition

Use the PostgresAddListPartition operation to add a new list partition. Only use this operation when your partitioned model uses the psqlextra.types.PostgresPartitioningMethod.LIST.

from django.db import migrations, models

from psqlextra.migrations.operations import PostgresAddRangePartition

class Migration(migrations.Migration):
    operations = [
        PostgresAddListPartition(
           model_name="mypartitionedmodel",
           name="pt1",
           values=["car", "boat"],
        ),
    ]

Adding a default partition

Use the PostgresAddDefaultPartition operation to add a new default partition. A default partition is the partition where records get saved that couldn’t fit in any other partition.

Note that you can only have one default partition per partitioned table/model.

from django.db import migrations, models

from psqlextra.migrations.operations import PostgresAddDefaultPartition

class Migration(migrations.Migration):
    operations = [
        PostgresAddDefaultPartition(
           model_name="mypartitionedmodel",
           name="default",
        ),
    ]

Deleting a default partition

Use the PostgresDeleteDefaultPartition operation to delete an existing default partition.

from django.db import migrations, models

from psqlextra.migrations.operations import PostgresDeleteDefaultPartition

class Migration(migrations.Migration):
    operations = [
        PostgresDeleteDefaultPartition(
           model_name="mypartitionedmodel",
           name="pt1",
        ),
    ]

Deleting a range partition

Use the psqlextra.migrations.operations.PostgresDeleteRangePartition operation to delete an existing range partition.

from django.db import migrations, models

from psqlextra.migrations.operations import PostgresDeleteRangePartition

class Migration(migrations.Migration):
    operations = [
        PostgresDeleteRangePartition(
           model_name="mypartitionedmodel",
           name="pt1",
        ),
    ]

Deleting a list partition

Use the PostgresDeleteListPartition operation to delete an existing list partition.

from django.db import migrations, models

from psqlextra.migrations.operations import PostgresDeleteListPartition

class Migration(migrations.Migration):
    operations = [
        PostgresDeleteListPartition(
           model_name="mypartitionedmodel",
           name="pt1",
        ),
    ]

Using the schema editor

Use the psqlextra.backend.PostgresSchemaEditor to manage partitions directly in a more imperative fashion. The schema editor is used by the migration operations described above.

Adding a range partition

from django.db import connection

connection.schema_editor.add_range_partition(
    model=MyPartitionedModel,
    name="pt1",
    from_values="2019-01-01",
    to_values="2019-02-01",
)

Adding a list partition

from django.db import connection

connection.schema_editor.add_list_partition(
    model=MyPartitionedModel,
    name="pt1",
    values=["car", "boat"],
)

Adding a default partition

from django.db import connection

connection.schema_editor.add_default_partition(
    model=MyPartitionedModel,
    name="default",
)

Deleting a partition

from django.db import connection

connection.schema_editor.delete_partition(
    model=MyPartitionedModel,
    name="default",
)

Adding/removing partitions automatically

psqlextra.partitioning.PostgresPartitioningManager an experimental helper class that can be called periodically to automatically create new partitions if you’re using range partitioning.

Note

There is currently no scheduler or command to automatically create new partitions. You’ll have to run this function in your own cron jobs.

The auto partitioner supports automatically creating yearly, monthly, weekly or daily partitions. Use the count parameter to configure how many partitions it should create ahead.

Partitioning strategies

Monthly partitioning

Partitions will be named [table_name]_[3-letter month name].

from psqlextra.partitioning import (
   PostgresPartitioningManager,
   partition_by_current_time,
)

# 3 partitions ahead, each partition is one month
manager = PostgresPartitioningManager(
   model=MyPartitionedModel,
   count=3,
   months=1,
)
manager.apply()

Weekly partitioning

Partitions will be named [table_name]_week_[week number].

from psqlextra.partitioning import (
   PostgresPartitioningManager,
   partition_by_current_time,
)

# 4 partitions ahead, each partition is 1 week
manager = PostgresPartitioningManager(
   model=MyPartitionedModel,
   count=4,
   weeks=1,
)
manager.apply()


# 6 partitions ahead, each partition is 2 weeks
manager = PostgresPartitioningManager(
   model=MyPartitionedModel,
   count=6,
   weeks=2,
)
manager.apply()

Switching partitioning strategies

When switching partitioning strategies, you might encounter the problem that partitions for part of a particular range already exist. In order to combat this, you can specify the start_from parameter to not create partitions for a date/time earlier than specified.