postgres=# CREATE TABLE cities (
postgres(#     name            text,
postgres(#     population      float,
postgres(#     altitude        int     -- in feet
postgres(# );
CREATE TABLE
postgres=# \d+ cities
                       Table "public.cities"
   Column   |       Type       | Modifiers | Storage  | Description 
------------+------------------+-----------+----------+-------------
 name       | text             |           | extended | 
 population | double precision |           | plain    | 
 altitude   | integer          |           | plain    | 
Has OIDs: no

postgres=# CREATE TABLE capitals (
postgres(#     state           char(2)
postgres(# ) INHERITS (cities);
CREATE TABLE
postgres=# \d+ capitals;
                      Table "public.capitals"
   Column   |       Type       | Modifiers | Storage  | Description 
------------+------------------+-----------+----------+-------------
 name       | text             |           | extended | 
 population | double precision |           | plain    | 
 altitude   | integer          |           | plain    | 
 state      | character(2)     |           | extended | 
Inherits: cities
Has OIDs: no

postgres=# insert into cities values('kms',10.23,1000);
INSERT 0 1
postgres=# insert into capitals values('kms',10.23,1000,'01');
INSERT 0 1
postgres=# select * from cities;
 name | population | altitude 
------+------------+----------
 kms  |      10.23 |     1000
 kms  |      10.23 |     1000
(2 rows)
                           ^
postgres=# select * from only cities;
 name | population | altitude 
------+------------+----------
 kms  |      10.23 |     1000
(1 row)

postgres=# create table streets(col1 char(1)) inherits(capitals);
insert into streets values ('kms',20.24,2100,02,'1');
INSERT 0 1

postgres=# select * from only cities;
 name | population | altitude 
------+------------+----------
 kms  |      10.23 |     1000
(1 row)

postgres=# select * from only capitals;
 name | population | altitude | state 
------+------------+----------+-------
 kms  |      10.23 |     1000 | 01
(1 row)

postgres=# select * from streets;
 name | population | altitude | state | col1 
------+------------+----------+-------+------
 kms  |      20.24 |     2100 | 2     | 1
(1 row)

postgres=# select * from cities;
 name | population | altitude 
------+------------+----------
 kms  |      10.23 |     1000
 kms  |      10.23 |     1000
 kms  |      20.24 |     2100
(3 rows)

FATAL:  could not create semaphores: No space left on device
[2012-10-24 16:49:55.313 KST][][][][][20731]DETAIL:  Failed system call was semget(5433033, 17, 03600).
[2012-10-24 16:49:55.313 KST][][][][][20731]HINT:  This error does *not* mean that you have run out of disk space.
 It occurs when either the system limit for the maximum number of semaphore sets (SEMMNI), or the system wide maximum number
 of semaphores (SEMMNS), would be exceeded.  You need to raise the respective kernel parameterively, reduce PostgreSQL's 
consumption of semaphores by reducing its max_connections parameter (currently 510).
 The PostgreSQL documentation contains more information about configuring your system for PostgreSQL.

$ ipcs -l

------ Shared Memory Limits --------
max number of segments = 4096
max seg size (kbytes) = 67108864
max total shared memory (kbytes) = 17179869184
min seg size (bytes) = 1

------ Semaphore Limits --------
max number of arrays = 128
max semaphores per array = 250
max semaphores system wide = 32000
max ops per semop call = 32
semaphore max value = 32767

------ Messages: Limits --------
max queues system wide = 16
max size of message (bytes) = 65536
default max size of queue (bytes) = 65536

$ vi /etc/sysctl.conf
kerlel.sem=250 256000 32 128    ## 네번째 값이 SEMMNI이고 이 값을 증가시켜야 합니다.(세마포어 배열의 최대갯수).
$ sysctl -p /etc/sysctl.conf    ## 수정한 값으로 리로드 합니다.

$ cd .src/contrib/dblink
$ make
$ make install

test=# create extension dblink;
CREATE extension

test=# select dblink_connect('db링크이름','hostaddr=호스트IP port=호스트PORT dbname=DB명 user=유저명 password=비밀번호');
 dblink_connect 
----------------
 OK
(1 row)
-- 조회(as 뒤에 select결과에 대한 type을 column별로 지정)
test=# select * from dblink('db2', 'select * from test') as t1(c1 char);
 c1 
----
 d
(1 row)
-- 접속해제
test=# select dblink_disconnect('db2');
 dblink_disconnect 
-------------------
 OK
(1 row)