openGauss 每日一练第10天

学习目标

表空间是数据的容器。掌握表空间的管理，包括创建表空间、删除表空间、重命名表空间、查看表空间的情况。

课程学习

通过使用表空间，管理员可以控制一个数据库安装的磁盘布局。

openGauss自带了两个表空间：pg_default和pg_global。

• 默认表空间pg_default：用来存储非共享系统表、用户表、用户表index、临时表、临时表index、内部临时表的默认表空间。对应存储目录为实例数据目录下的base目录。

• 共享表空间pg_global：用来存放共享系统表的表空间。对应存储目录为实例数据目录下的global目录。

准备

• 切换用户，连接数据库

  su - omm
  gsql -r
  

1、创建表空间t_tbspace、用户test，并使用test，在这个表空间上创建表t1

omm=#CREATE  TABLESPACE t_tbspace RELATIVE LOCATION 'tablespace/t_tbspace';
CREATE TABLESPACE

omm=#CREATE USER test IDENTIFIED BY 'abcd@1234';
NOTICE:  The encrypted password contains MD5 ciphertext, which is not secure.
CREATE ROLE

omm=# \c omm test
Password for user test: 
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "omm" as user "test".

-- 使用 test 用户 登录到库 omm ，并创建表 t1
omm=# \c omm test
Password for user test: 
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "omm" as user "test".
omm=> CREATE TABLE  t1(col01  int ) TABLESPACE t_tbspace;
ERROR:  permission denied for tablespace t_tbspace
DETAIL:  N/A
-- 可以看到，我们未对test 用户授权，创建表空间失败，我们切换到omm 用户 为test 赋予tablespace 的 create 权限

omm=> \c omm omm
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "omm" as user "omm".
omm=# grant CREATE  on TABLESPACE t_tbspace to test;
GRANT
-- 再次切换到 test 用户，创建表空间 t_tbspace 成功
omm=# \c omm test
Password for user test: 
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "omm" as user "test".
omm=> CREATE TABLE  t1(col01  int ) TABLESPACE t_tbspace;
CREATE TABLE

2、查看表空间t_tbspace的oid^[1]和大小

-- 查看表空间 t_tbspace 的oid
select oid,* from pg_tablespace;

omm=> select oid,* from pg_tablespace ;
  oid  |  spcname   | spcowner |         spcacl         | spcoptions | spcmaxsize | relative 
-------+------------+----------+------------------------+------------+------------+----------
  1663 | pg_default |       10 |                        |            |            | f
  1664 | pg_global  |       10 |                        |            |            | f
 16389 | t_tbspace  |       10 | {omm=C/omm,test=C/omm} |            |            | t
(3 rows)

-- 查看表空间 t_tbspace 的大小 
omm=> SELECT PG_TABLESPACE_SIZE('t_tbspace');

 pg_tablespace_size 
--------------------
               8192
(1 row)

PG_TABLESPACE_SIZE 为系统提供的对象管理函数 PG文档参考链接 9.26.6

3、查看数据库在默认表空间下有哪些对象

omm=> with objectInDefaultTS as  ( 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' )
 select *  from objectInDefaultTS  where relname not like 'pg_%' and relname not like 'gs_%' and relname not like 'sql_%'
 order by relpages desc;
                                  
                 relname                  | relkind | relpages | pg_size_pretty | reltablespace | relowner 
------------------------------------------+---------+----------+----------------+---------------+----------
 streaming_gather_agg_index               | i       |        2 | 16 kB          |             0 |       10
 snapshot_id_key                          | i       |        1 | 8192 bytes     |             0 |       10
 streaming_cont_query_lookupidxid_index   | i       |        1 | 8192 bytes     |             0 |       10
 streaming_cont_query_defrelid_index      | i       |        1 | 8192 bytes     |             0 |       10
 streaming_cont_query_schema_change_index | i       |        1 | 8192 bytes     |             0 |       10
 streaming_reaper_status_id_index         | i       |        1 | 8192 bytes     |             0 |       10
 streaming_reaper_status_oid_index        | i       |        1 | 8192 bytes     |             0 |       10
 snapshot_pkey                            | i       |        1 | 8192 bytes     |             0 |       10
 statement_history_time_idx               | i       |        1 | 8192 bytes     |             0 |       10
 streaming_stream_oid_index               | i       |        1 | 8192 bytes     |             0 |       10
 streaming_stream_relid_index             | i       |        1 | 8192 bytes     |             0 |       10
 streaming_cont_query_relid_index         | i       |        1 | 8192 bytes     |             0 |       10
 streaming_cont_query_matrelid_index      | i       |        1 | 8192 bytes     |             0 |       10
 plan_table_data                          | r       |        0 | 0 bytes        |             0 |       10
 statement_history                        | r       |        0 | 0 bytes        |             0 |       10
 streaming_stream                         | r       |        0 | 0 bytes        |             0 |       10
 snapshot                                 | r       |        0 | 0 bytes        |             0 |       10
 streaming_cont_query_id_index            | i       |        1 | 8192 bytes     |             0 |       10
 streaming_cont_query_oid_index           | i       |        1 | 8192 bytes     |             0 |       10
 streaming_reaper_status                  | r       |        0 | 0 bytes        |             0 |       10
 streaming_cont_query                     | r       |        0 | 0 bytes        |             0 |       10
(21 rows)

WITH 子句 [ 参考连接 ]

在 PostgreSQL 中，WITH 子句提供了一种编写辅助语句的方法，有助于将复杂的大型查询分解为更简单的表单，便于阅读，也可以当做一个为查询而存在的临时表。WITH 子句是在多次执行子查询时特别有用，允许我们在查询中通过它的名称(可能是多次)引用它。

4、查看数据库在非默认表空间下有哪些对象

 select relname,relkind,relpages,pg_size_pretty(pg_relation_size(a.oid)),  reltablespace,relowner
   from pg_class a, pg_tablespace tb
   where a.relkind in ('r', 'i')
   and a.reltablespace=tb.oid
   and tb.spcname='t_tbspace'
   order by a.relpages desc;
   
   relname | relkind | relpages | pg_size_pretty | reltablespace | relowner 
---------+---------+----------+----------------+---------------+----------
 t1      | r       |        0 | 0 bytes        |         16389 |    16390
(1 row)

5、重命名表空间

-- 命名表空间t_tbspace为app_tbs

omm=# alter tablespace t_tbspace rename to app_tbs;
ALTER TABLESPACE

-- 查看表空间是否已改名

omm=# \db
            List of tablespaces
    Name    | Owner |       Location       
------------+-------+----------------------
 app_tbs    | omm   | tablespace/t_tbspace
 pg_default | omm   | 
 pg_global  | omm   | 
(3 rows)

6、删除表空间

-- 删除表空间，可以看到表空间如果还有使用，是删不掉的
omm=# drop tablespace app_tbs ;
ERROR:  tablespace "app_tbs" is not empty

-- 查看 app_tbs表空间被那些表使用
omm=# select * from pg_tables where tablespace = 'app_tbs';
 schemaname | tablename | tableowner | tablespace | hasindexes | hasrules | hastriggers | tablecreator |            created            |         last_ddl_time         
------------+-----------+------------+------------+------------+----------+-------------+--------------+-------------------------------+-------------------------------
 test       | t1        | test       | app_tbs    | f          | f        | f           | test         | 2022-12-04 10:59:46.495473+08 | 2022-12-04 10:59:46.495473+08
(1 row)

-- 查看 app_tbs表空间被那些索引使用
omm=# SELECT * FROM pg_indexes WHERE tablespace='app_tbs';
 schemaname | tablename | indexname | tablespace | indexdef 
------------+-----------+-----------+------------+----------
(0 rows)

-- 删除 对应的表 再删除表空间
omm=# drop table test.t1 ;
DROP TABLE
omm=# drop tablespace app_tbs ; 
DROP TABLESPACE