CUBRID学习笔记 20 默认的并发规则

;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