4、postgresql拓展表空间

base是数据保存目录，

OID：对象标识符，无符号4字节整数，

数据库的oid在pg_database中，表，索引，序列等OID存储在pg_class中

表空间：pg最大的逻辑存储单元，表索引数据库都分配到对应表空间，创建数据库时会默认创建表空间，pg_default和pg_global两个表空间。

还可以自定义表空间，分配在不同性能的磁盘上

-bash-4.2$ mkdir new_space
-bash-4.2$ psql
psql (10.21)
Type "help" for help.

postgres=# \db+
                                  List of tablespaces
    Name    |  Owner   | Location | Access privileges | Options |  Size   | Description 
------------+----------+----------+-------------------+---------+---------+-------------
 pg_default | postgres |          |                   |         | 1447 MB | 
 pg_global  | postgres |          |                   |         | 574 kB  | 
(2 rows)

postgres=# create tablespace new_space location '/var/lib/pgsql/new_space';
CREATE TABLESPACE
postgres=# \db+
                                          List of tablespaces
    Name    |  Owner   |         Location         | Access privileges | Options |  Size   | Description 
------------+----------+--------------------------+-------------------+---------+---------+-------------
 new_space  | postgres | /var/lib/pgsql/new_space |                   |         | 0 bytes | 
 pg_default | postgres |                          |                   |         | 1447 MB | 
 pg_global  | postgres |                          |                   |         | 574 kB  | 

在新的表空间上创建表

postgres=# create tablespace new_space location '/var/lib/pgsql/new_space';
CREATE TABLESPACE
postgres=# \db+
                                          List of tablespaces
    Name    |  Owner   |         Location         | Access privileges | Options |  Size   | Description 
------------+----------+--------------------------+-------------------+---------+---------+-------------
 new_space  | postgres | /var/lib/pgsql/new_space |                   |         | 0 bytes | 
 pg_default | postgres |                          |                   |         | 1447 MB | 
 pg_global  | postgres |                          |                   |         | 574 kB  | 
(3 rows)

postgres=# create table new_test(id int ) tablespace new_space ;
CREATE TABLE

数据块在磁盘中叫page[读写的最小单位默认大小8kb],在内存中叫buffer

表和索引叫relation

行称为tuple