Re: Clarification of behaviour when dropping partitions

On Wed, 2024-12-04 at 14:22 +0100, Bolaji Wahab wrote:
> I have these two partitioned tables, with referential integrity. The tables
> are structured in such a way that we have 1 to 1 mapping between their
> partitions. This is achieved with a foreign key.
>
> CREATE TABLE parent (
>     partition_date date NOT NULL,
>     id uuid NOT NULL,
>     external_transaction_id uuid NOT NULL,
>
>     CONSTRAINT parent_pkey
>         PRIMARY KEY (id, partition_date),
>
>     CONSTRAINT parent_external_transaction_id_key
>         UNIQUE (external_transaction_id, partition_date)
> ) PARTITION BY RANGE (partition_date);
>
> CREATE TABLE parent_2024_12_01
>     PARTITION OF public.parent
>     FOR VALUES FROM ('2024-12-01') TO ('2024-12-02');
>
> CREATE TABLE parent_2024_12_02
>     PARTITION OF public.parent
>     FOR VALUES FROM ('2024-12-02') TO ('2024-12-03');
>
> [...]
>
> CREATE TABLE child (
>     partition_date date NOT NULL,
>     transaction_id uuid NOT NULL,
>     key            text NOT NULL,
>     value          text NOT NULL,
>
>     CONSTRAINT child_pkey
>         PRIMARY KEY (transaction_id, key, partition_date),
>
>     CONSTRAINT child_transaction_id_fkey
>         FOREIGN KEY (transaction_id, partition_date)
>         REFERENCES parent (id, partition_date)
> ) PARTITION BY RANGE (partition_date);
>
> CREATE TABLE child_2024_12_01
>     PARTITION OF child
>     FOR VALUES FROM ('2024-12-01') TO ('2024-12-02');
>
> CREATE TABLE child_2024_12_02
>     PARTITION OF public.child
>     FOR VALUES FROM ('2024-12-02') TO ('2024-12-03');

I recommend that you don't create the foreign key constraint between the
partitioned tables, but between the individual partitions.

That will make detaching and dropping partitions easier, and you will have
the same integrity guarantees.

Yours,
Laurenz Albe