Re: The problem is related to concurrent resquests - Mailing list pgsql-admin

Please keep the list posted!

Nguyen Hoai Nam wrote:
> Step1: I would to create "network" table with three columns including id, network_id, subnet. It's
> like below:
>
> +--------------------+---------------+
> |  id    |network_id |  subnet       |
> +------------------------------------+
> |   1    |     aa    |192.168.1.0/24 |
> |        |           |               |
> |        |           |               |
> +--------+-----------+---------------+
>
> This table have condition: If a new record with overlap subnet and same value's network_id then DB
> will not allow inster to DB
>
> For example:
>
> Request1: test=> INSERT INTO network VALUES (2, aa,'192.168.1.0/24');
> The result is that DB doesn't allow to insert to DB. Becase it violate overlap CIDR and same value's
> network_id
>
> Request2: test=> INSERT INTO network VALUES (3, bb,'192.168.1.0/24');
> The result is that DB ALLOW to insert to DB. Because this reqest has network_id = bb, this value is
> different with existing value (aa)

This is getting more difficult, but you can *still* do it with an exclusion
constraint in PostgreSQL. You need to install an extension with a
GiST operator class for varchar:

test=# CREATE EXTENSION btree_gist;

Then you can do the following:

   CREATE TABLE network (
      id integer PRIMARY KEY,
      network_id varchar(20) NOT NULL,
      subnet cidr NOT NULL
   );

   ALTER TABLE network
      ADD CONSTRAINT network_subnet_excl
         EXCLUDE USING gist (
            network_id gist_text_ops WITH =,
            subnet inet_ops WITH &&
         );

Then you get:

test=> INSERT INTO network VALUES (1, 'aa','192.168.1.0/24');
INSERT 0 1

test=> INSERT INTO network VALUES (2, 'aa', '192.168.1.0/24');
ERROR:  conflicting key value violates exclusion constraint "network_subnet_excl"
DETAIL:  Key (network_id, subnet)=(aa, 192.168.1.0/24) conflicts with existing key (network_id, subnet)=(aa, 192.168.1.0/24).

test=> INSERT INTO network VALUES (3, 'bb', '192.168.1.0/24');
INSERT 0 1


As Kevin said, using SERIALIZABLE transactions is an alternative, but a constraint
is probably better.

Yours,
Laurenz Albe