This may sound more elaborate than it's worth, but I don't know of
a better way to avoid a table scan.

You want to index on a computed value that is a common prefix of your
FROM and TO fields.

The next step is to search on a fixed SET of prefixes of different lengths. For example, some of your ranges might be common in the first 3 bytes of ipaddr, some in two, some in only one.

You create and index on one common prefix of either 1,2 or 3 bytes, for each row.

Your query then looks something like (pardon my ignorance in PGSQL)

        select  *
        from    ip2location
        where   ip2prefix in (
                network(:myaddr || '/8'),
                network(:myaddr || '/16'),
                network(:myaddr || '/24'),
                :myaddr --- assuming single-address ranges are possible
                )
        and :myaddr between ip_address_from and ip_address_to

Although this looks a little gross, it hits very few records.
It also adapts cleanly to a join between ip2location and a table of
ip addrs.

Gabriele Bartolini wrote:
Hi guys,

   please consider this scenario. I have this table:

CREATE TABLE ip2location (
    ip_address_from BIGINT NOT NULL,
    ip_address_to BIGINT NOT NULL,
    id_location BIGINT NOT NULL,
    PRIMARY KEY (ip_address_from, ip_address_to)
);

I created a cluster on its primary key, by running:
CLUSTER ip2location_ip_address_from_key ON ip2location;

This allowed me to organise data in a more efficient way: the data that is contained are ranges of IP addresses with empty intersections; for every IP class there is a related location's ID. The total number of entries is 1392443.

For every IP address I have, an application retrieves the corresponding location's id from the above table, by running a query like:

SELECT id_location FROM ip2location WHERE '11020000111' >= ip_address_from AND '11020000111' <= ip_address_to;

For instance, by running the 'EXPLAIN ANALYSE' command, I get this "funny" result:


QUERY PLAN
---------------------------------------------------------------------------------------------------------------------


Seq Scan on ip2location (cost=0.00..30490.65 rows=124781 width=8) (actual time=5338.120..40237.283 rows=1 loops=1)
Filter: ((1040878301::bigint >= ip_address_from) AND (1040878301::bigint <= ip_address_to))
Total runtime: 40237.424 ms



With other data, that returns an empty set, I get:

explain SELECT id_location FROM ip2location WHERE '11020000111' >= ip_address_from AND '11020000111' <= ip_address_to;

QUERY PLAN
-------------------------------------------------------------------------------------------------------


Index Scan using ip2location_ip_address_from_key on ip2location (cost=0.00..419.16 rows=140 width=8)
Index Cond: ((11020000111::bigint >= ip_address_from) AND (11020000111::bigint <= ip_address_to))



I guess the planner chooses the best of the available options for the first case, the sequential scan. This is not confirmed though by the fact that, after I ran "SET enable_scan TO off", I got this:
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------------------------


Index Scan using ip2location_ip_address_from_key on ip2location (cost=0.00..31505.73 rows=124781 width=8) (actual time=2780.172..2780.185 rows=1 loops=1)
Index Cond: ((1040878301::bigint >= ip_address_from) AND (1040878301::bigint <= ip_address_to))
Total runtime: 2780.359 ms



Is this a normal case or should I worry? What am I missing? Do you have any suggestion or comment to do (that would be extremely appreciated)? Is the CLUSTER I created worthwhile or not?


Thank you,
-Gabriele

--
Gabriele Bartolini: Web Programmer, ht://Dig & IWA/HWG Member, ht://Check maintainer
Current Location: Prato, Toscana, Italia
[EMAIL PROTECTED] | http://www.prato.linux.it/~gbartolini | ICQ#129221447
> "Leave every hope, ye who enter!", Dante Alighieri, Divine Comedy, The Inferno



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