openGauss每日一练第9天 |PG_DATABASE

今日目标：学习表空间与数据库对象的关系,了解oid的含义。

openGauss在内部使用对象标识符（OID）作为各种系统表的主键。系统不会给用户创建的表增加一个OID系统字段，OID类型代表一个对象标识符。

OID类型：主要作为数据库系统表中字段使用。

系统表

• PG_DATABASE

  系统表存储关于可用数据库的信息。
  

• PG_TABLESPACE
  PG_TABLESPACE系统表存储表空间信息。
  

1.实验准备

• 创建表空间music_tbs ，并在该表空间下创建数据库musicdb

创建user1，并授予sysadmin权限

omm=# create tablespace music_tbs relative location 'tablespace/test_ts1';
CREATE TABLESPACE
omm=# create database musicdb with tablespace music_tbs ;
CREATE DATABASE
omm=# create user user1 sysadmin  identified by 'gauss@1234';
NOTICE:  The encrypted password contains MD5 ciphertext, which is not secure.
CREATE ROLE
omm=# \db
           List of tablespaces
    Name    | Owner |      Location       
------------+-------+---------------------
 music_tbs  | omm   | tablespace/test_ts1
 pg_default | omm   | 
 pg_global  | omm   | 
(3 rows)

omm=# \l
                         List of databases
   Name    | Owner | Encoding | Collate | Ctype | Access privileges 
-----------+-------+----------+---------+-------+-------------------
 musicdb   | omm   | UTF8     | C       | C     | 
 omm       | omm   | UTF8     | C       | C     | 
 postgres  | omm   | UTF8     | C       | C     | 
 template0 | omm   | UTF8     | C       | C     | =c/omm           +
           |       |          |         |       | omm=CTc/omm
 template1 | omm   | UTF8     | C       | C     | =c/omm           +
           |       |          |         |       | omm=CTc/omm
(5 rows)

omm=# \du
                                                              List of roles
 Role name |                                                    Attributes                                                    | Member of 
-----------+------------------------------------------------------------------------------------------------------------------+-----------
 gaussdb   | Sysadmin                                                                                                         | {}
 omm       | Sysadmin, Create role, Create DB, Replication, Administer audit, Monitoradmin, Operatoradmin, Policyadmin, UseFT | {}
 user1     | Sysadmin                                                                                                         | {}

omm=# 

• openGauss的默认表空间查看

musicdb=> select datname,dattablespace,spcname from pg_database d, pg_tablespace t where d.dattablespace=t.oid;
  datname  | dattablespace |  spcname   
-----------+---------------+------------
 template1 |          1663 | pg_default
 omm       |          1663 | pg_default
 musicdb   |         16389 | music_tbs
 template0 |          1663 | pg_default
 newdb1    |         16396 | newtbs1
 postgres  |          1663 | pg_default
(6 rows)

• 查询数据库的默认表空间上的对象

  select relname, relkind, relpages,pg_size_pretty(pg_relation_size(a.oid)),reltablespace,relowner  
  from pg_class a  
  where a.relkind in ('r', 'i')  
  and reltablespace='0'  
  order by a.relpages desc;
  

2.课后作业

2.1.创建表空间newtbs1

\db // 查看表表空间

omm=# create tablespace newtbs1 relative location 'tablespace/tablespace_test';
CREATE TABLESPACE
omm=# \db
               List of tablespaces
    Name    | Owner |          Location          
------------+-------+----------------------------
 music_tbs  | omm   | tablespace/test_ts1
 newtbs1    | omm   | tablespace/tablespace_test
 pg_default | omm   | 
 pg_global  | omm   | 
(4 rows)
 
omm=# select oid ,* from pg_tablespace;
  oid  |  spcname   | spcowner | spcacl | spcoptions | spcmaxsize | relative 
-------+------------+----------+--------+------------+------------+----------
  1663 | pg_default |       10 |        |            |            | f
  1664 | pg_global  |       10 |        |            |            | f
 16389 | music_tbs  |       10 |        |            |            | t
 16398 | newtbs1    |       10 |        |            |            | t
(4 rows)

2.2 创建3个数据库newdb1、newdb2、newdb3，默认表空间为newtbs1

omm=# create database newdb1 with tablespace = newtbs1 ;
CREATE DATABASE 
omm=# create database newdb2 with tablespace newtbs1 ;
CREATE DATABASE
omm=# create database newdb3 with tablespace = newtbs1 ;
CREATE DATABASE
omm=# 

2.3 使用sql查看表空间newtbs1上有几个数据库

omm=# select * from pg_tablespace ;
  spcname   | spcowner | spcacl | spcoptions | spcmaxsize | relative 
------------+----------+--------+------------+------------+----------
 pg_default |       10 |        |            |            | f
 pg_global  |       10 |        |            |            | f
 music_tbs  |       10 |        |            |            | t
 newtbs1    |       10 |        |            |            | t
(4 rows)
omm=# select datname,dattablespace,spcname from pg_database d ,pg_tablespace t where d.dattablespace = t.oid;
  datname  | dattablespace |  spcname   
-----------+---------------+------------
 template1 |          1663 | pg_default
 omm       |          1663 | pg_default
 musicdb   |         16389 | music_tbs
 template0 |          1663 | pg_default
 musicdb2  |         16389 | music_tbs
 musicdb3  |         16389 | music_tbs
 musicdb1  |         16389 | music_tbs
 postgres  |          1663 | pg_default
 newdb1    |         16398 | newtbs1
 newdb2    |         16398 | newtbs1
 newdb3    |         16398 | newtbs1
(11 rows)
omm=# select datname,dattablespace,spcname from pg_database d, pg_tablespace t where d.dattablespace = t.oid and spcname = 'newtbs1';
 datname | dattablespace | spcname 
---------+---------------+---------
 newdb1  |         16398 | newtbs1
 newdb2  |         16398 | newtbs1
 newdb3  |         16398 | newtbs1
(3 rows)

omm=#

2.4. 在文件系统中查看表空间newtbs1中的多个数据库

omm=# select oid,* from pg_tablespace where spcname = 'newtbs1';
  oid  | spcname | spcowner | spcacl | spcoptions | spcmaxsize | relative 
-------+---------+----------+--------+------------+------------+----------
 16398 | newtbs1 |       10 |        |            |            | t
(1 row)

omm=# select oid,datname,dattablespace from pg_database where dattablespace = '16398';
oid  | datname | dattablespace 
-------+---------+---------------
 16399 | newdb1  |         16398
 16400 | newdb2  |         16398
 16401 | newdb3  |         16398
 (3 rows)
 omm=# select datname ,dattablespace,spcname from pg_database d,pg_tablespace t where d.dattablespace = t.oid and t.spcname = 'newtbs1';
 datname | dattablespace | spcname 
---------+---------------+---------
 newdb1  |         16398 | newtbs1
 newdb2  |         16398 | newtbs1
 newdb3  |         16398 | newtbs1
(3 rows)

omm=# 

退出数据库，进入文件系统查看表空间

omm=# \q
omm@modb:/var/lib/opengauss/data/pg_tblspc$ pwd
/var/lib/opengauss/data/pg_tblspc
omm@modb:/var/lib/opengauss/data/pg_tblspc$ ls
16389  16398
omm@modb:/var/lib/opengauss/data/pg_tblspc$ cd 16398
omm@modb:/var/lib/opengauss/data/pg_tblspc/16398$ ls -lrht
total 4.0K
drwx------ 6 omm omm 4.0K Dec  2 22:01 PG_9.2_201611171_gaussdb
omm@modb:/var/lib/opengauss/data/pg_tblspc/16398$ cd PG_9.2_201611171_gaussdb/
omm@modb:/var/lib/opengauss/data/pg_tblspc/16398/PG_9.2_201611171_gaussdb$ ls
16399  16400  16401  pgsql_tmp
omm@modb:/var/lib/opengauss/data/pg_tblspc/16398/PG_9.2_201611171_gaussdb$