postgres 数据库只读设置

锁定的实现方法有若干种。

1、硬锁定，直接将数据库切换到恢复模式，绝对不会有写操作出现。

2、软锁定，设置default_transaction_read_only为on，默认开启的事务为只读事务。用户如果使用begion transaction read write可破解。

1 锁定实例

硬锁定

1、配置 recovery.conf

recovery_target_timeline = 'latest'  
standby_mode = on

2、重启数据库

pg_ctl restart -m fast

3、硬锁定，不可破解

postgres=# select pg_is_in_recovery();  
 pg_is_in_recovery   
-------------------  
 t  
(1 row)  
  
postgres=# insert into t1 values (1);  
ERROR:  cannot execute INSERT in a read-only transaction  
  
postgres=# begin transaction read write;  
ERROR:  cannot set transaction read-write mode during recovery

软锁定

1、设置default_transaction_read_only

postgres=# alter system set default_transaction_read_only=on;  
ALTER SYSTEM

2、重载配置

postgres=# select pg_reload_conf();  
 pg_reload_conf   
----------------  
 t  
(1 row)

3、所有会话自动进入read only的默认事务模式。

reload前

postgres=# show default_transaction_read_only ;  
 default_transaction_read_only   
-------------------------------  
 off  
(1 row)

reload后

postgres=# show default_transaction_read_only ;  
 default_transaction_read_only   
-------------------------------  
 on  
(1 row)  
  
postgres=# insert into t1 values (1);  
ERROR:  cannot execute INSERT in a read-only transaction

4、软锁定可破解

postgres=# begin transaction read write;  
BEGIN  
postgres=# insert into t1 values (1);  
INSERT 0 1  
postgres=# end;  
COMMIT

2 解锁实例

硬解锁

1、重命名recovery.conf到recovery.done

cd $PGDATA  
  
mv recovery.conf recovery.done