postgresql cidr查找子块

Question

I'm looking for a way to get direct children networks from cidr blocks stored in postgresql using the builtin cidr type.

Example database

CREATE TABLE nets (
    id serial primary key,
    net cidr
);
INSERT INTO nets (net) VALUES 
    ('10.1.0.0/16'),
    ('10.1.0.0/20'),
    ('10.1.1.0/24'),
    ('10.1.1.8/29'),
    ('10.1.1.32/28'),
    ('10.2.15.0/24'),
    ('10.2.15.64/27')

The desired query should fe

• return 10.1.0.0/20 for searchkey 10.1.0.0/16
• 10.1.1.8/29 and 10.1.1.32/28 for searchkey 10.1.1.0/24

What I came up with is ( http://sqlfiddle.com/#!15/2b4b5/1 ):

SELECT
  id,
  net
FROM 
  nets n
WHERE 
  net << '10.1.1.0/24' AND
  '10.1.1.0/24' IN (
    SELECT 
      net 
    FROM
      nets
    WHERE
      net >> n.net
    ORDER BY
      net DESC
    LIMIT 1
  )
ORDER BY 
  net

This gives the desired result, but it does not scale. Even with only a few thousand entries in the database this gets terribly slow.

Is there another way to achieve this, without adding an explicit parent/child relationship to the database model?

Answer 1

Update : This is a variant, transformed from the Nested set model , it could be even faster (mainly on 9.4+ with the inet_ops GiST index):

SELECT c.id, c.net
FROM   nets c
WHERE  c.net << '10.1.1.0/24'
AND    NOT EXISTS(
  SELECT 1
  FROM   nets AS m
  WHERE  c.net << m.net AND m.net << '10.1.1.0/24'
);

Original answer :

A simple EXCEPT should scale better with larger input-sets (it won't calculate a sub-plan for every child network):

(SELECT id, net
 FROM   nets
 WHERE  net << '10.1.1.0/24')
EXCEPT
(SELECT c.id, c.net
 FROM   nets p
 JOIN   nets c ON c.net << p.net
 WHERE  p.net << '10.1.1.0/24')
ORDER BY net;

Note : with smaller input-sets, the EXCEPT variant might be even slower than your query.

But to maximize performance (both with this & with your query), you should use some index.

If you have PostgreSQL 9.4+, you should use the new inet_ops GiST index:

CREATE INDEX nets_inet_net_gist ON nets USING gist (inet(net) inet_ops);

Otherwise, you can use the network_ops btree index:

CREATE INDEX nets_inet_net_btree ON nets USING btree (inet(net) network_ops);

While inet_ops can directly use the << operator, network_ops will transform your expression to something like that:

Index Cond: (((net)::inet > '10.1.1.0/24'::inet) AND ((net)::inet <= '10.1.1.255'::inet))