openGauss每日一练第16天|《openGauss事务控制》学习心得体会和课后练习

openGauss每日一练第16天|《openGauss事务控制》学习心得体会和课后练习

学习openGauss事务控制
事务是用户定义的一个数据库操作序列，这些操作要么全做要么全不做，是一个不可分割的工作单位

课程学习

连接数据库

#第一次进入等待15秒
#数据库启动中...
su - omm
gsql -r

1.事务控制

–通过START TRANSACTION和BEGIN语法启动事务
-以默认方式启动事务

START TRANSACTION;
select * from pg_class limit 1;
END；

–开启一个事务，设置事务的隔离级别为READ COMMITTED，访问模式为READ ONLY

BEGIN;
SET LOCAL TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
show transaction_read_only;
select * from pg_class limit 1;
create schema tpcds10;
commit;

omm=# BEGIN;
BEGIN
omm=# SET LOCAL TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
SET
omm=# 
omm=# show transaction_read_only;


omm=#  transaction_read_only 
-----------------------
 on
(1 row)
omm=# select * from pg_class limit 1;
   relname    | relnamespace | reltype | reloftype | relowner | relam | relfilenode | reltable
space | relpages | reltuples | relallvisible | reltoastrelid | reltoastidxid | reldeltarelid |
 reldeltaidx | relcudescrelid | relcudescidx | relhasindex | relisshared | relpersistence | re
lkind | relnatts | relchecks | relhasoids | relhaspkey | relhasrules | relhastriggers | relhas
subclass | relcmprs | relhasclusterkey | relrowmovement | parttype | relfrozenxid |      relac
l       | reloptions | relreplident | relfrozenxid64 | relbucket | relbucketkey 
--------------+--------------+---------+-----------+----------+-------+-------------+---------
      |       29 |         0 | f          | f          | f           | f              | f     
         | 0        | f                | f              | n        | 0            | {omm=arwdD
 pg_statistic |           11 |   11334 |         0 |       10 |     0 |       13689 |         
    0 |       18 |       476 |            18 |          2840 |             0 |             0 |
           0 |              0 |            0 | t           | f           | p              | r 
------+----------+-----------+---------------+---------------+---------------+---------------+
-------------+----------------+--------------+-------------+-------------+----------------+---
------+----------+-----------+------------+------------+-------------+----------------+-------
---------+----------+------------------+----------------+----------+--------------+-----------
--------+------------+--------------+----------------+-----------+--------------

xt/omm} |            | n            |           7891 |           | 
(1 row)
omm=# create schema tpcds10;
ERROR:  cannot execute CREATE SCHEMA in a read-only transaction
omm=# commit;
ROLLBACK

–以隔离级别为repeatable read，读/写方式启动事务

show transaction_isolation;
START TRANSACTION ISOLATION LEVEL repeatable read READ WRITE;
show transaction_isolation;
show transaction_read_only;
select * from pg_class limit 1;
create schema tpcds10;
rollback;

omm=# show transaction_isolation;
 transaction_isolation 
-----------------------
 read committed
(1 row)

omm=# START TRANSACTION ISOLATION LEVEL repeatable read READ WRITE;
START TRANSACTION
omm=# show transaction_isolation;
 transaction_isolation 
-----------------------
 repeatable read
(1 row)

omm=# show transaction_read_only;
(1 row)

omm=#  transaction_read_only 
-----------------------
 off

omm=# select * from pg_class limit 1;
   relname    | relnamespace | reltype | reloftype | relowner | relam | relfilenode | reltable
space | relpages | reltuples | relallvisible | reltoastrelid | reltoastidxid | reldeltarelid |
 reldeltaidx | relcudescrelid | relcudescidx | relhasindex | relisshared | relpersistence | re
lkind | relnatts | relchecks | relhasoids | relhaspkey | relhasrules | relhastriggers | relhas
subclass | relcmprs | relhasclusterkey | relrowmovement | parttype | relfrozenxid |      relac
l       | reloptions | relreplident | relfrozenxid64 | relbucket | relbucketkey 
--------------+--------------+---------+-----------+----------+-------+-------------+---------
------+----------+-----------+---------------+---------------+---------------+---------------+
-------------+----------------+--------------+-------------+-------------+----------------+---
------+----------+-----------+------------+------------+-------------+----------------+-------
---------+----------+------------------+----------------+----------+--------------+-----------
--------+------------+--------------+----------------+-----------+--------------
 pg_statistic |           11 |   11334 |         0 |       10 |     0 |       13689 |         
    0 |       18 |       476 |            18 |          2840 |             0 |             0 |
           0 |              0 |            0 | t           | f           | p              | r 
      |       29 |         0 | f          | f          | f           | f              | f     
         | 0        | f                | f              | n        | 0            | {omm=arwdD
xt/omm} |            | n            |           7891 |           | 
(1 row)

omm=# create schema tpcds10;
CREATE SCHEMA
omm=# rollback;
ROLLBACK

–事务回滚，schema没有创建成功

\dn+ tpcds10;

2.savepoint

–保存点是事务中的一个特殊记号，它允许将那些在它建立后执行的命令全部回滚，把事务的状态恢复到保存点所在的时刻

CREATE TABLE table1(a int);
START TRANSACTION;
INSERT INTO table1 VALUES (1);

–建立保存点

SAVEPOINT my_savepoint;
INSERT INTO table1 VALUES (2);

–回滚保存点

ROLLBACK TO SAVEPOINT my_savepoint;

–删除保存点

RELEASE SAVEPOINT my_savepoint;
INSERT INTO table1 VALUES (3);
COMMIT;
omm=# CREATE TABLE table1(a int);
CREATE TABLE
omm=# START TRANSACTION;
START TRANSACTION
omm=# INSERT INTO table1 VALUES (1);
INSERT 0 1
omm=# SAVEPOINT my_savepoint;
SAVEPOINT
omm=# INSERT INTO table1 VALUES (2);
INSERT 0 1
omm=# ROLLBACK TO SAVEPOINT my_savepoint;
ROLLBACK
omm=# RELEASE SAVEPOINT my_savepoint;
RELEASE
omm=# INSERT INTO table1 VALUES (3);
INSERT 0 1
omm=# COMMIT;
COMMI

–查询表的内容，会同时看到1和3,不能看到2，因为2被回滚

SELECT * FROM table1;

课程作业

1.以默认方式启动事务1，修改事务隔离级别，查看transaction_isolation

begin;
show transaction_isolation;
START TRANSACTION ISOLATION LEVEL repeatable read READ WRITE;
show transaction_isolation;
end;

2.以读写方式启动事务2，创建新表，修改事务为只读事务，查看transaction_read_only，并向表中插入记录

begin;
create table test(id int);
SET LOCAL TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
show transaction_read_only;
insert into test values(1);
commit;

3.启动事务3，对表进行增删改查，并用到创建savepoint，回滚savepoint和删除savepoint

begin;
insert into test values(1);
SAVEPOINT my_savepoint;
insert into test values(2);
ROLLBACK TO SAVEPOINT my_savepoint;
select * from test;
release SAVEPOINT my_savepoint;
INSERT INTO table1 VALUES (3);
commit;

4.清理数据

create table test;