Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.sai.msu.su/~megera/postgres/gist/code/7.1/README.intarray Дата изменения: Mon Mar 19 17:29:02 2001 Дата индексирования: Sat Dec 22 07:52:30 2007 Кодировка: Поисковые слова: http www.badastronomy.com bad tv foxapollo.html

This is an implementation of RD-tree data structure using GiST interface
of PostgreSQL. It has built-in lossy compression - must be declared
in index creation - with (islossy). Current implementation provides index
support for one-dimensional array of int4's - gist__int_ops, suitable for
small and medium size of arrays (used on default), and gist__intbig_ops for
indexing large arrays (we use superimposed signature with length of 4096
bits to represent sets).

All work was done by Teodor Sigaev (teodor@stack.net) and Oleg Bartunov
(oleg@sai.msu.su). See http://www.sai.msu.su/~megera/postgres/gist
for additional information.

CHANGES:

March 19, 2001
1. Added support for toastable keys
2. Improved split algorithm for intbig (selection speedup is about 30%)

INSTALLATION:

gmake
gmake install
-- load functions
psql < _int.sql

REGRESSION TEST:

gmake installcheck

EXAMPLE USAGE:

create table message (mid int not null,sections int[]);
create table message_section_map (mid int not null,sid int not null);

-- create indices
CREATE unique index message_key on message ( mid );
CREATE unique index message_section_map_key2 on message_section_map (sid, mid );
CREATE INDEX message_rdtree_idx on message using gist ( sections gist__int_ops) with ( islossy );

-- select some messages with section in 1 OR 2 - OVERLAP operator
select message.mid from message where message.sections && '{1,2}';

-- select messages contains in sections 1 AND 2 - CONTAINS operator
select message.mid from message where message.sections @ '{1,2}';
-- the same, CONTAINED operator
select message.mid from message where '{1,2}' ~ message.sections;

BENCHMARK:

subdirectory bench contains benchmark suite.
cd ./bench
1. createdb TEST
2. psql TEST < ../_int.sql
3. ./create_test.pl | psql TEST
4. ./bench.pl - perl script to benchmark queries, supports OR, AND queries
with/without RD-Tree. Run script without arguments to
see availbale options.

a)test without RD-Tree (OR)
./bench.pl -d TEST -s 1,2 -v
b)test with RD-Tree
./bench.pl -d TEST -s 1,2 -v -r

BENCHMARKS:

Size of table : 200000
Size of table : 268538

Distribution of messages by sections:

section 0: 73899 messages
section 1: 16298 messages
section 50: 1241 messages
section 99: 705 messages

old - without RD-Tree support,
new - with RD-Tree

+----------+---------------+----------------+
|Search set|OR, time in sec|AND, time in sec|
| +-------+-------+--------+-------+
| | old | new | old | new |
+----------+-------+-------+--------+-------+
| 1| 1.427| 0.215| -| -|
+----------+-------+-------+--------+-------+
| 99| 1.029| 0.018| -| -|
+----------+-------+-------+--------+-------+
| 1,2| 1.829| 0.334| 5.654| 0.042|
+----------+-------+-------+--------+-------+
| 1,2,50,60| 2.057| 0.359| 5.044| 0.007|
+----------+-------+-------+--------+-------+