Message-ID: <928c165be24ee307c2fbaa29a2c6360eb8a00e02.camel@cybertec.at>
Subject: Re: Clarification of behaviour when dropping partitions
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Bolaji Wahab <bolajiwahab23@gmail.com>, pgsql-general@postgresql.org
Date: Wed, 04 Dec 2024 18:20:55 +0100
In-Reply-To: <CA+f_mLPhCa_G3nRrB4=e3trqCSQ88x56ZvfeweH-AhwS77xEGg@mail.gmail.com>
References: 
	<CA+f_mLPhCa_G3nRrB4=e3trqCSQ88x56ZvfeweH-AhwS77xEGg@mail.gmail.com>
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On Wed, 2024-12-04 at 14:22 +0100, Bolaji Wahab wrote:
> I have these two partitioned tables, with=C2=A0referential integrity. The=
 tables
> are structured=C2=A0in such=C2=A0a way that we have 1 to 1 mapping betwee=
n their
> partitions. This is achieved with a foreign key.
>=20
> CREATE TABLE parent (
> =C2=A0 =C2=A0 partition_date date NOT NULL,
> =C2=A0 =C2=A0 id uuid NOT NULL,
> =C2=A0 =C2=A0 external_transaction_id uuid NOT NULL,
>=20
> =C2=A0 =C2=A0 CONSTRAINT parent_pkey
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 PRIMARY KEY (id, partition_date),
>=20
> =C2=A0 =C2=A0 CONSTRAINT parent_external_transaction_id_key
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 UNIQUE (external_transaction_id, partition_da=
te)
> ) PARTITION BY RANGE (partition_date);
>=20
> CREATE TABLE parent_2024_12_01
> =C2=A0 =C2=A0 PARTITION OF public.parent
> =C2=A0 =C2=A0 FOR VALUES FROM ('2024-12-01') TO ('2024-12-02');
>=20
> CREATE TABLE parent_2024_12_02
> =C2=A0 =C2=A0 PARTITION OF public.parent
> =C2=A0 =C2=A0 FOR VALUES FROM ('2024-12-02') TO ('2024-12-03');
>=20
> [...]
>=20
> CREATE TABLE child (
> =C2=A0 =C2=A0 partition_date date NOT NULL,
> =C2=A0 =C2=A0 transaction_id uuid NOT NULL,
> =C2=A0 =C2=A0 key =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0text NOT NULL,
> =C2=A0 =C2=A0 value =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0text NOT NULL,
>=20
> =C2=A0 =C2=A0 CONSTRAINT child_pkey
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 PRIMARY KEY (transaction_id, key, partition_d=
ate),
>=20
> =C2=A0 =C2=A0 CONSTRAINT child_transaction_id_fkey
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 FOREIGN KEY (transaction_id, partition_date)
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 REFERENCES parent (id, partition_date)
> ) PARTITION BY RANGE (partition_date);
>=20
> CREATE TABLE child_2024_12_01
> =C2=A0 =C2=A0 PARTITION OF child
> =C2=A0 =C2=A0 FOR VALUES FROM ('2024-12-01') TO ('2024-12-02');
>=20
> CREATE TABLE child_2024_12_02
> =C2=A0 =C2=A0 PARTITION OF public.child
> =C2=A0 =C2=A0 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