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