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 carefully.
Table partitioning¶
PostgresPartitionedModel
adds support for PostgreSQL Declarative Table Partitioning.
The following partitioning methods are available:
PARTITION BY RANGE
PARTITION BY LIST
PARTITION BY HASH
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.
Use
psqlextra.types.PostgresPartitioningMethod.RANGE
toPARTITION BY RANGE
Use
psqlextra.types.PostgresPartitioningMethod.LIST
toPARTITION BY LIST
Use
psqlextra.types.PostgresPartitioningMethod.HASH
toPARTITION BY HASH
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 a migration that creates the partitioned table with a default partition.
Warning
Always use python manage.py pgmakemigrations
for partitioned models.
The model must be created by the PostgresCreatePartitionedModel
operation.
Do not use the standard python manage.py makemigrations
command for partitioned models. Django will issue a standard CreateModel
operation. Doing this will not create a partitioned table and all subsequent operations will fail.
Adding/removing partitions manually¶
Postgres does not have support for automatically creating new partitions as needed. Therefore, 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.
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.backend.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",
),
]
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.backend.migrations.operations import PostgresAddListPartition
class Migration(migrations.Migration):
operations = [
PostgresAddListPartition(
model_name="mypartitionedmodel",
name="pt1",
values=["car", "boat"],
),
]
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.backend.migrations.operations import PostgresAddDefaultPartition
class Migration(migrations.Migration):
operations = [
PostgresAddDefaultPartition(
model_name="mypartitionedmodel",
name="default",
),
]
Use the PostgresDeleteDefaultPartition
operation to delete an existing default partition.
from django.db import migrations, models
from psqlextra.backend.migrations.operations import PostgresDeleteDefaultPartition
class Migration(migrations.Migration):
operations = [
PostgresDeleteDefaultPartition(
model_name="mypartitionedmodel",
name="pt1",
),
]
Use the psqlextra.backend.migrations.operations.PostgresDeleteRangePartition
operation to delete an existing range partition.
from django.db import migrations, models
from psqlextra.backend.migrations.operations import PostgresDeleteRangePartition
class Migration(migrations.Migration):
operations = [
PostgresDeleteRangePartition(
model_name="mypartitionedmodel",
name="pt1",
),
]
Use the PostgresDeleteListPartition
operation to delete an existing list partition.
from django.db import migrations, models
from psqlextra.backend.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¶
Time-based partitioning¶
from dateutil.relativedelta import relativedelta
from psqlextra.partitioning import (
PostgresPartitioningManager,
PostgresCurrentTimePartitioningStrategy,
PostgresTimePartitionSize,
partition_by_current_time,
)
manager = PostgresPartitioningManager([
# 3 partitions ahead, each partition is one month
# delete partitions older than 6 months
# partitions will be named `[table_name]_[year]_[3-letter month name]`.
PostgresPartitioningConfig(
model=MyPartitionedModel,
strategy=PostgresCurrentTimePartitioningStrategy(
size=PostgresTimePartitionSize(months=1),
count=3,
max_age=relativedelta(months=6),
),
),
# 6 partitions ahead, each partition is two weeks
# delete partitions older than 8 months
# partitions will be named `[table_name]_[year]_week_[week number]`.
PostgresPartitioningConfig(
model=MyPartitionedModel,
strategy=PostgresCurrentTimePartitioningStrategy(
size=PostgresTimePartitionSize(weeks=2),
count=6,
max_age=relativedelta(months=8),
),
),
# 12 partitions ahead, each partition is 5 days
# old partitions are never deleted, `max_age` is not set
# partitions will be named `[table_name]_[year]_[month]_[month day number]`.
PostgresPartitioningConfig(
model=MyPartitionedModel,
strategy=PostgresCurrentTimePartitioningStrategy(
size=PostgresTimePartitionSize(wdyas=5),
count=12,
),
),
])
# these are the default arguments
partioning_plan = manager.plan(
skip_create=False,
skip_delete=False,
using='default'
)
# prints a list of partitions to be created/deleted
partitioning_plan.print()
# apply the plan
partitioning_plan.apply(using='default');
Custom strategy¶
You can create a custom partitioning strategy by implementing the psqlextra.partitioning.PostgresPartitioningStrategy
interface.
You can look at psqlextra.partitioning.PostgresCurrentTimePartitioningStrategy
as an example.
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 use the psqlextra.partitioning.PostgresTimePartitioningStrategy
and specify the start_datetime parameter. As a result, no partitions will be created before the given date/time.