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