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 <database> < _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 <message>: 200000
Size of table <message_section_map>: 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|
+----------+-------+-------+--------+-------+