事务型数据库，比较重要的事务控制来了，let's study it!!!
1.连接数据库
su - omm
gsql -r
2.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
omm=# start transaction;
START TRANSACTION
omm=# select * from pg_class limit 1;
relname | relnamespace | reltype | reloftype | relowner | relam | relfilenode | reltablespace | relpages | reltuples | relallv
isible | reltoastrelid | reltoastidxid | reldeltarelid | reldeltaidx | relcudescrelid | relcudescidx | relhasindex | relisshared | r
elpersistence | relkind | relnatts | relchecks | relhasoids | relhaspkey | relhasrules | relhastriggers | relhassubclass | relcmprs
| relhasclusterkey | relrowmovement | parttype | relfrozenxid | relacl | reloptions | relreplident | relfrozenxid64 | rel
bucket | relbucketkey
--------------+--------------+---------+-----------+----------+-------+-------------+---------------+----------+-----------+--------
-------+---------------+---------------+---------------+-------------+----------------+--------------+-------------+-------------+--
--------------+---------+----------+-----------+------------+------------+-------------+----------------+----------------+----------
+------------------+----------------+----------+--------------+-------------------+------------+--------------+----------------+----
-------+--------------
| r | 29 | 0 | f | f | f | f | f | 0
| f | f | n | 0 | {omm=arwdDxt/omm} | | n | 7891 |
|
(1 row)
pg_statistic | 11 | 11334 | 0 | 10 | 0 | 13689 | 0 | 18 | 476 |
18 | 2840 | 0 | 0 | 0 | 0 | 0 | t | f | p
omm=# end;
omm=# COMMIT
–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
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 | relallv
isible | reltoastrelid | reltoastidxid | reldeltarelid | reldeltaidx | relcudescrelid | relcudescidx | relhasindex | relisshared | r
elpersistence | relkind | relnatts | relchecks | relhasoids | relhaspkey | relhasrules | relhastriggers | relhassubclass | relcmprs
0 | f | f | f | f | f | 0
| f | f | n | 0 | {omm=arwdDxt/omm} | | n | 7891 |
|
(1 row)
| relhasclusterkey | relrowmovement | parttype | relfrozenxid | relacl | reloptions | relreplident | relfrozenxid64 | rel
bucket | relbucketkey
--------------+--------------+---------+-----------+----------+-------+-------------+---------------+----------+-----------+--------
-------+---------------+---------------+---------------+-------------+----------------+--------------+-------------+-------------+--
--------------+---------+----------+-----------+------------+------------+-------------+----------------+----------------+----------
+------------------+----------------+----------+--------------+-------------------+------------+--------------+----------------+----
-------+--------------
pg_statistic | 11 | 11334 | 0 | 10 | 0 | 13689 | 0 | 18 | 476 |
18 | 2840 | 0 | 0 | 0 | 0 | 0 | t | f | p
| r | 29 | omm=#
omm=# omm=#
omm=#
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
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 | relallv
isible | reltoastrelid | reltoastidxid | reldeltarelid | reldeltaidx | relcudescrelid | relcudescidx | relhasindex | relisshared | r
elpersistence | relkind | relnatts | relchecks | relhasoids | relhaspkey | relhasrules | relhastriggers | relhassubclass | relcmprs
| relhasclusterkey | relrowmovement | parttype | relfrozenxid | relacl | reloptions | relreplident | relfrozenxid64 | rel
bucket | relbucketkey
--------------+--------------+---------+-----------+----------+-------+-------------+---------------+----------+-----------+--------
-------+---------------+---------------+---------------+-------------+----------------+--------------+-------------+-------------+--
--------------+---------+----------+-----------+------------+------------+-------------+----------------+----------------+----------
+------------------+----------------+----------+--------------+-------------------+------------+--------------+----------------+----
-------+--------------
pg_statistic | 11 | 11334 | 0 | 10 | 0 | 13689 | 0 | 18 | 476 |
18 | 2840 | 0 | 0 | 0 | 0 | 0 | t | f | p
| f | f | n | 0 | {omm=arwdDxt/omm} | | n | 7891 |
|
(1 row)
| r | 29 | 0 | f | f | f | f | f | 0
omm=#
omm=#
omm=#
omm=# omm=#
omm=# create schema tpcds10;
CREATE SCHEMA
omm=# rollback;
ROLLBACK
omm=#
omm=# omm=#
–事务回滚，schema没有创建成功
查看一下schema信息
omm=# \dn+ tpcds10;
List of schemas
Name | Owner | Access privileges | Description
------+-------+-------------------+-------------
(0 rows)
omm=#
3.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
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
omm=# SAVEPOINT my_savepoint;
SAVEPOINT
omm=# INSERT INTO table1 VALUES (2);
omm=# INSERT 0 1
–回滚保存点
omm=# ROLLBACK TO SAVEPOINT my_savepoint;
ROLLBACK
–删除保存点
omm=# RELEASE SAVEPOINT my_savepoint;
RELEASE
omm=# INSERT INTO table1 VALUES (3);
INSERT 0 1
omm=# 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
omm=# SELECT * FROM table1;
a
---
1
3
(2 rows)
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
omm=# start transaction;
START TRANSACTION
omm=# set local transaction isolation level read committed read only;
SET
omm=# end;
COMMIT
omm=# show transaction_isolation;
transaction_isolation
-----------------------
read committed
(1 row)
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
omm=# START TRANSACTION ISOLATION LEVEL read committed READ WRITE;
omm=# show transaction_isolation;
transaction_isolation
-----------------------
read committed
(1 row)
omm=# show transaction_read_only;
transaction_read_only
-----------------------
off
(1 row)
omm=# create table test(id integer,name varchar(20));
CREATE TABLE
omm=#
omm=# insert into test values(1,'aaa');
INSERT 0 1
omm=#
omm=# commit;
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 TEST VALUES(1,'BBB');
INSERT 0 1
omm=# SAVEPOINT point1;
SAVEPOINT
omm=# insert into test values(2,'ccc');
INSERT 0 1
omm=# ROLLBACK TO SAVEPOINT point1;
ROLLBACK
omm=# RELEASE SAVEPOINT point1;
RELEASE
omm=# INSERT INTO test VALUES (3,'ddd');
omm=# INSERT 0 1
omm=#
omm=# COMMIT;
COMMIT
omm=#
omm=#
4.清理数据
omm=# drop table test;
DROP TABLE
