第十六课 openGauss事务控制
学习目标
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
###学习内容如下
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;
–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;
–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;
–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
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
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
4.清理数据
show transaction_isolation;
START TRANSACTION;
show transaction_isolation;
SET local TRANSACTION ISOLATION LEVEL repeatable read;
show transaction_isolation;
rollback;
START TRANSACTION ISOLATION LEVEL read committed READ WRITE;
CREATE TABLE t1(a int);
show transaction_read_only;
SET LOCAL TRANSACTION READ ONLY;
show transaction_read_only;
insert into t1 values(1);
rollback;
CREATE TABLE t2(a int);
START TRANSACTION;
INSERT INTO t2 VALUES (1);
SAVEPOINT my_savepoint1;
INSERT INTO t2 VALUES (2);
ROLLBACK TO SAVEPOINT my_savepoint1;
RELEASE SAVEPOINT my_savepoint1;
INSERT INTO t2 VALUES (3);
COMMIT;
SELECT * FROM t2;
drop table t1;
drop table t2;
课后作业记录
omm=#
omm=#
omm=# START TRANSACTION;
START TRANSACTION
omm=# select * from pg_class limit 1;
relname | relnamespace | reltype | reloftype | relowner | relam | relfilenode | reltablespace |
relpages | reltuples | relallvisible | reltoastrelid | reltoastidxid | reldeltarelid | reldeltaidx |
relcudescrelid | relcudescidx | relhasindex | relisshared | relpersistence | relkind | relnatts | re
lchecks | relhasoids | relhaspkey | relhasrules | relhastriggers | relhassubclass | relcmprs | relhas
clusterkey | relrowmovement | parttype | relfrozenxid | relacl | 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=arwdDxt/omm} | | n
| 7891 | |
(1 row)
omm=# END;
COMMIT
omm=#
omm=# BEGIN;
BEGIN
omm=# SET LOCAL TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
SET
omm=# show transaction_read_only;
transaction_read_only
-----------------------
on
(1 row)
omm=# select * from pg_class limit 1;
relname | relnamespace | reltype | reloftype | relowner | relam | relfilenode | reltablespace |
relpages | reltuples | relallvisible | reltoastrelid | reltoastidxid | reldeltarelid | reldeltaidx |
relcudescrelid | relcudescidx | relhasindex | relisshared | relpersistence | relkind | relnatts | re
lchecks | relhasoids | relhaspkey | relhasrules | relhastriggers | relhassubclass | relcmprs | relhas
clusterkey | relrowmovement | parttype | relfrozenxid | relacl | 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=arwdDxt/omm} | | n
| 7891 | |
(1 row)
omm=# create schema tpcds10;
ERROR: cannot execute CREATE SCHEMA in a read-only transaction
omm=# commit;
ROLLBACK
omm=#
omm=#
omm=#
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;
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 | reltoastidxid | reldeltarelid | reldeltaidx |
relcudescrelid | relcudescidx | relhasindex | relisshared | relpersistence | relkind | relnatts | re
lchecks | relhasoids | relhaspkey | relhasrules | relhastriggers | relhassubclass | relcmprs | relhas
clusterkey | relrowmovement | parttype | relfrozenxid | relacl | reloptions | relreplident
| relfrozenxid64 | relbucket | relbucketkey
--------------+--------------+---------+-----------+----------+-------+-------------+---------------+
----------+-----------+---------------+---------------+---------------+---------------+-------------+
----------------+--------------+-------------+-------------+----------------+---------+----------+---
--------+------------+------------+-------------+----------------+----------------+----------+-------
-----------+----------------+----------+--------------+-------------------+------------+-------------
-+----------------+-----------+--------------
pg_statistic | 11 | 11334 | 0 | 10 | 0 | 13689 | 0 |
| f | n | 0 | {omm=arwdDxt/omm} | | n
| 7891 | |
(1 row)
18 | 476 | 18 | 2840 | 0 | 0 | 0 |
0 | 0 | t | f | p | r | 29 |
0 | f | f | f | f | f | 0 | f
omm=# create schema tpcds10;
CREATE SCHEMA
omm=# rollback;
ROLLBACK
omm=#
omm=# \dn+ tpcds10;
List of schemas
Name | Owner | Access privileges | Description
------+-------+-------------------+-------------
(0 rows)
omm=#
omm=# CREATE TABLE table1(a int);
CREATE TABLE
omm=# START TRANSACTION;
START TRANSACTION
omm=# INSERT INTO table1 VALUES (1);
INSERT 0 1
omm=#
omm=# SAVEPOINT my_savepoint;
SAVEPOINT
omm=# INSERT INTO table1 VALUES (2);
INSERT 0 1
omm=#
omm=# ROLLBACK TO SAVEPOINT my_savepoint;
ROLLBACK
omm=#
omm=# select * from table1;
a
---
1
(1 row)
omm=# RELEASE SAVEPOINT my_savepoint;
omm=# INSERT INTO table1 VALUES (3);
RELEASE
INSERT 0 1
omm=# COMMIT;
COMMIT
omm=#
omm=# SELECT * FROM table1;
a
---
1
3
(2 rows)
omm=#
omm=#
omm=# show transaction_isolation;
transaction_isolation
-----------------------
read committed
(1 row)
omm=# START TRANSACTION;
START TRANSACTION
omm=#
omm=# show transaction_isolation;
transaction_isolation
-----------------------
read committed
(1 row)
omm=# SET local TRANSACTION ISOLATION LEVEL repeatable read;
SET
omm=# show transaction_isolation;
(1 row)
omm=# transaction_isolation
-----------------------
repeatable read
omm=# rollback;
ROLLBACK
omm=#
omm=#
omm=#
omm=#
omm=# show transaction_isolation;
transaction_isolation
-----------------------
read committed
(1 row)
omm=# START TRANSACTION ISOLATION READ WRITE;
ERROR: syntax error at or near "READ"
LINE 1: START TRANSACTION ISOLATION READ WRITE;
^
omm=# CREATE TABLE t1(a int);
CREATE TABLE
omm=#
omm=# dtop table t1;
ERROR: syntax error at or near "dtop"
LINE 1: dtop table t1;
^
omm=#
omm=# drop table t1;
DROP TABLE
omm=#
omm=#
omm=#
omm=#
omm=# START TRANSACTION ISOLATION LEVEL read committed READ WRITE;
START TRANSACTION
omm=# CREATE TABLE t1(a int);
CREATE TABLE
omm=#
omm=# show transaction_read_only;
transaction_read_only
-----------------------
off
(1 row)
omm=# SET LOCAL TRANSACTION READ ONLY;
SET
omm=#
omm=# show transaction_read_only;
transaction_read_only
-----------------------
on
(1 row)
omm=# insert into t1 values(1);
ERROR: cannot execute INSERT in a read-only transaction
omm=#
omm=# rollback;
ROLLBACK
omm=#
omm=#
omm=#
omm=# CREATE TABLE t2(a int);
omm=# CREATE TABLE
omm=# START TRANSACTION;
START TRANSACTION
omm=# INSERT INTO t2 VALUES (1);
INSERT 0 1
omm=#
omm=#
omm=#
omm=# SAVEPOINT my_savepoint1;
SAVEPOINT
omm=# INSERT INTO t2 VALUES (2);
omm=# INSERT 0 1
omm=#
omm=# ROLLBACK TO SAVEPOINT my_savepoint1;
ROLLBACK
omm=#
omm=#
omm=# select * from t2;
a
---
1
(1 row)
omm=#
omm=# RELEASE SAVEPOINT my_savepoint1;
RELEASE
omm=# INSERT INTO t2 VALUES (3);
COMMIT;
INSERT 0 1
omm=# COMMIT
omm=#
omm=# SELECT * FROM t2;
a
---
1
3
(2 rows)
omm=#
omm=#
omm=# drop table t1;
drop table t2;
ERROR: table "t1" does not exist
omm=# DROP TABLE
omm=#
omm=#
omm=# \d
List of relations
Schema | Name | Type | Owner | Storage
--------+--------+-------+-------+----------------------------------
public | item | table | omm | {orientation=row,compression=no}
public | table1 | table | omm | {orientation=row,compression=no}
(2 rows)
omm=#
omm=#
最后修改时间：2021-12-30 21:42:43
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