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[数据库]CUBRID学习笔记 20 默认的并发规则


默认的设置是ISOLATION LEVEL 3

语法 SET TRANSACTION ISOLATION LEVEL 3;

最笨.官网的图不错看图吧

session 1

session 2

;autocommit off

AUTOCOMMIT IS OFF

 

SET TRANSACTION ISOLATION LEVEL 3;

 

Isolation level set to:

REPEATABLE READ SCHEMA, READ UNCOMMITTED INSTANCES.

;autocommit off

AUTOCOMMIT IS OFF

 

SET TRANSACTION ISOLATION LEVEL 3;

 

Isolation level set to:

REPEATABLE READ SCHEMA, READ UNCOMMITTED INSTANCES.

--creating a table

 

CREATE TABLE isol3_tbl(host_year integer, nation_code char(3));

CREATE UNIQUE INDEX on isol3_tbl(nation_code, host_year);

INSERT INTO isol3_tbl VALUES (2008, 'AUS');

 

COMMIT;

 

 

--selecting records from the table

SELECT * FROM isol3_tbl;

    host_year  nation_code

===================================

         2008  'AUS'

INSERT INTO isol3_tbl VALUES (2004, 'AUS');

 

INSERT INTO isol3_tbl VALUES (2000, 'NED');

 

/* able to insert new rows even if tran 2 uncommitted */

 

 

SELECT * FROM isol3_tbl;

    host_year  nation_code

===================================

         2008  'AUS'

         2004  'AUS'

         2000  'NED'

 

/* dirty read may occur so that tran_2 can select new rows uncommitted by tran_1 */

ROLLBACK;

 

 

SELECT * FROM isol3_tbl;

    host_year  nation_code

===================================

         2008  'AUS'

 

/* unrepeatable read may occur so that selected results are different */

INSERT INTO isol3_tbl VALUES (1994, 'FRA');

 

DELETE FROM isol3_tbl

WHERE nation_code = 'AUS' and

host_year=2008;

 

/* able to delete rows even if tran 2 uncommitted */

 

 

SELECT * FROM isol3_tbl;

    host_year  nation_code

===================================

         1994  'FRA'

ALTER TABLE isol3_tbl

ADD COLUMN gold INT;

 

/* unable to alter the table schema until tran 2 committed */

 

 

/* repeatable read is ensured while tran_1 is altering table schema */

 

SELECT * FROM isol3_tbl;

    host_year  nation_code

===================================

         1994  'FRA'

 

COMMIT;

 

SELECT * FROM isol3_tbl;

COMMIT;

host_year  nation_code  gold

===================================

  1994  'FRA'           NULL