Re: inet/cidr indexes almost not used

OK, see the FAQ on index usage and run some tests.

I have just added the following to our FAQ section on index usage:

<P>If you believe the optimizer is incorrect in choosing a
sequential scan, use <CODE>SET enable_seqscan TO 'off'</CODE> and
run tests to see if an index scan is indeed faster.</P>

---------------------------------------------------------------------------

Gleb Kouzmenko wrote:
> Your name : Gleb Kouzmenko
> Your email address : gleb(at)well(dot)ru
>
>
> System Configuration
> ---------------------
> Architecture (example: Intel Pentium) : Intel Pentium
>
> Operating System (example: Linux 2.0.26 ELF) : Linux 2.4.19
>
> PostgreSQL version (example: PostgreSQL-7.3.1): PostgreSQL-7.3.1 (REL7_3_STABLE 2003-01-16)
>
> Compiler used (example: gcc 2.95.2) : gcc 3.2
>
>
> Please enter a FULL description of your problem:
> ------------------------------------------------
>
> I almost never could not use single-column index on cidr or inet fields
> for ops <<,<<=,>>,>>= - optimizer does seq scan instead of index scan.
>
> index scan happens only when
> ( ops is << or ops is <<= ) and column is left-side operand
>
>
> Examples
> ____________
> [table and rows from src/test/regress/sql/inet.sql]
>
> CREATE TABLE INET_TBL (c cidr, i inet);
> INSERT INTO INET_TBL (c, i) VALUES ('192.168.1', '192.168.1.226/24');
> ... inserts from inet.sql
> create index inet_idx1 on inet_tbl(i);
> create index inet_idx2 on inet_tbl(c);
> =========
>
> test=# set enable_seqscan to off;
> SET
> test=# explain select * from inet_tbl where i<<'192.168.1.0/24'::cidr;
> QUERY PLAN
> -------------------------------------------------------------------------------
> Index Scan using inet_idx1 on inet_tbl (cost=0.00..4.68 rows=7 width=64)
> Index Cond: ((i > '192.168.1.0/24'::inet) AND (i <= '192.168.1.255'::inet))
> Filter: (i << '192.168.1.0/24'::inet)
> (2 rows)
>
> test=# explain select * from inet_tbl where '192.168.1.0/24'::cidr>>i;
> QUERY PLAN
> -------------------------------------------------------------------------
> Seq Scan on inet_tbl (cost=100000000.00..100000001.17 rows=7 width=64)
> Filter: ('192.168.1.0/24'::inet >> i)
> (2 rows)
>
> test=# explain select * from inet_tbl where c>>'192.168.1.0/24'::cidr;
> QUERY PLAN
> -------------------------------------------------------------------------
> Seq Scan on inet_tbl (cost=100000000.00..100000001.17 rows=7 width=64)
> Filter: (c >> '192.168.1.0/24'::cidr)
> (2 rows)
>
> test=# explain select * from inet_tbl where '192.168.1.0/24'::cidr<<c;
> QUERY PLAN
> -------------------------------------------------------------------------
> Seq Scan on inet_tbl (cost=100000000.00..100000001.17 rows=7 width=64)
> Filter: ('192.168.1.0/24'::cidr << c)
> (2 rows)
>
>
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