openGauss每日一练第16天|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 第十六课
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;
START TRANSACTION;
select * from pg_class limit 1;
END；

omm=# START TRANSACTION;
omm=# START TRANSACTION
select * from pg_class limit 1;
relname | relnamespace | reltype | reloftype | relowner | relam | relfilenode | reltablespace | relpages | reltuples | relallvisible | reltoastrelid | reltoastidx
id | reldeltarelid | reldeltaidx | relcudescrelid | relcudescidx | relhasindex | relisshared | relpersistence | relkind | relnatts | relchecks | relhasoids | relhaspkey
| relhasrules | relhastriggers | relhassubclass | relcmprs | relhasclusterkey | relrowmovement | parttype | relfrozenxid | relacl | reloptions | relrepliden
t | relfrozenxid64 | relbucket | relbucketkey
--------------±-------------±--------±----------±---------±------±------------±--------------±---------±----------±--------------±--------------±-----------
—±--------------±------------±---------------±-------------±------------±------------±---------------±--------±---------±----------±-----------±----------
-±------------±---------------±---------------±---------±-----------------±---------------±---------±-------------±------------------±-----------±-----------
–±---------------±----------±-------------
pg_statistic | 11 | 11334 | 0 | 10 | 0 | 13689 | 0 | 18 | 476 | 18 | 2840 |
| 7891 | |
(1 row)

0 | 0 | 0 | 0 | 0 | t | f | p | r | 29 | 0 | f | f
| f | f | f | 0 | f | f | n | 0 | {omm=arwdDxt/omm} | | n
omm=# 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;

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=# SET LOCAL TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
ERROR: current transaction is aborted, commands ignored until end of transaction block, firstChar[Q]
omm=# show transaction_read_only;
ERROR: current transaction is aborted, commands ignored until end of transaction block, firstChar[Q]
omm=# select * from pg_class limit 1;
ERROR: current transaction is aborted, commands ignored until end of transaction block, firstChar[Q]
omm=# create schema tpcds10;
ERROR: current transaction is aborted, commands ignored until end of transaction block, firstChar[Q]
omm=# commit;
ROLLBACK
omm=#

–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)

show transaction_read_only;
omm=# transaction_read_only

off
(1 row)

omm=# select * from pg_class limit 1;
relname | relnamespace | reltype | reloftype | relowner | relam | relfilenode | reltablespace | relpages | reltuples | relallvisible | reltoastrelid | reltoastidx
id | reldeltarelid | reldeltaidx | relcudescrelid | relcudescidx | relhasindex | relisshared | relpersistence | relkind | relnatts | relchecks | relhasoids | relhaspkey
| relhasrules | relhastriggers | relhassubclass | relcmprs | relhasclusterkey | relrowmovement | parttype | relfrozenxid | relacl | reloptions | relrepliden
t | 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=arwdDxt/omm} | | n
| 7891 | |
(1 row)

omm=# create schema tpcds10;
CREATE SCHEMA
omm=# rollback;
ROLLBACK
omm-#
–事务回滚，schema没有创建成功

\dn+ tpcds10;
omm-# \dn+ tpcds10;
List of schemas
Name | Owner | Access privileges | Description
------±------±------------------±------------
(0 rows)

omm-#

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);

omm=# CREATE TABLE table1(a int);
CREATE TABLE
omm=# START TRANSACTION;
START TRANSACTION
omm=# INSERT INTO table1 VALUES (1);
INSERT 0 1

–建立保存点

SAVEPOINT my_savepoint;
INSERT INTO table1 VALUES (2);

omm=# SAVEPOINT my_savepoint;
SAVEPOINT
omm=# INSERT INTO table1 VALUES (2);
INSERT 0 1

–回滚保存点

ROLLBACK TO SAVEPOINT my_savepoint;

omm=# ROLLBACK TO SAVEPOINT my_savepoint;
ROLLBACK

–删除保存点

RELEASE SAVEPOINT my_savepoint;
INSERT INTO table1 VALUES (3);
COMMIT;

omm=# RELEASE SAVEPOINT my_savepoint;
RELEASE
omm=# INSERT INTO table1 VALUES (3);
INSERT 0 1
omm=# COMMIT;
COMMIT
–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;

omm=# SELECT * FROM table1;
omm=#
a

1
3
(2 rows)

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

START TRANSACTION;
omm=# START TRANSACTION ;
START TRANSACTION
BEGIN;
SET LOCAL TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
show transaction_read_only;
show transaction_isolation;
omm=# BEGIN;
WARNING: there is already a transaction in progress
BEGIN
omm=# SET LOCAL TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
omm=# SET
show transaction_read_only;
transaction_read_only

on
(1 row)

omm=# show transaction_isolation;
transaction_isolation

read committed
(1 row)

omm=# END;
COMMIT

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
START TRANSACTION;
SET LOCAL TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
show transaction_isolation;
end;
mm=# START TRANSACTION;
START TRANSACTION
omm=# SET LOCAL TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
SET
omm=# show transaction_isolation;
transaction_isolation

read committed
(1 row)

omm=# end;
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
omm=# start transaction;
START TRANSACTION
omm=# insert into ues (1),(2),(3),(4);
INSERT 0 4
omm=# delete from t1 where id=2;
DELETE 1
omm=# update t1 set id=10 where id=3;
UPDATE 1
omm=# savepoint a2;
SAVEPOINT
omm=# insert into t1 values (8);
INSERT 0 1
omm=# rollback to savepoint a2;
ROLLBACK
omm=# release savepoint a2;
RELEASE
omm=# insert into t1 values(9);
INSERT 0 1
omm=# commit;
COMMIT

4.清理数据
drop table t1;