MariaDB 10.5

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select version();

version()

10.5.10-MariaDB

SHOW VARIABLES LIKE '%isolation%';

Variable_name
Value

tx_isolation
REPEATABLE-READ

CREATE TABLE x (y INT, z VARCHAR (25));
INSERT INTO x VALUES (1, 'One'), (2, 'Two'), (3, 'Three'); 
SELECT * FROM x;

y
z

1
One

2
Two

3
Three

START TRANSACTION;

SELECT NOW(6);

SELECT * FROM x;

SELECT NOW(6);

COMMIT;

NOW(6)

2021-05-13 15:57:19.780260

y
z

1
One

2
Two

3
Three

NOW(6)

2021-05-13 15:57:19.780387

SET SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE;
SHOW VARIABLES LIKE '%isolation%';

Variable_name
Value

tx_isolation
SERIALIZABLE

START TRANSACTION;

SELECT NOW(6);

SELECT * FROM x;

SELECT NOW(6);

COMMIT;

NOW(6)

2021-05-13 15:57:19.781859

y
z

1
One

2
Two

3
Three

NOW(6)

2021-05-13 15:57:19.781981

SHOW VARIABLES LIKE '%isolation%';

Variable_name
Value

tx_isolation
SERIALIZABLE