How to set timeout for "SELECT FOR UPDATE" in transaction in PostgreSQL?

Question

I have product table with id, name and stock as shown below.

product table:

id	name	stock
1	Apple	10
2	Orange	20

Then, after T1 runs SELECT FOR UPDATE, T2 needs to wait for T1 to commit for a long time to run SELECT FOR UPDATE as shown below because SELECT FOR UPDATE doesn't have timeout by default:

Flow	Transaction 1 (T1)	Transaction 2 (T2)	Explanation
Step 1	BEGIN;		T1 starts.
Step 2		BEGIN;	T2 starts.
Step 3	SELECT stock FROM product WHERE id = 2 FOR UPDATE; 20		With "SELECT FOR UPDATE", T1 reads 20.
Step 4		SELECT stock FROM product WHERE id = 2 FOR UPDATE;	T2 needs to wait for T1 to commit to read stock with "SELECT FOR UPDATE".
Step 5		Waiting...	...
Step 6		Waiting...	...
Step ...		Waiting...	...
Step ...		Waiting...	...
Step ...		Waiting...	...
Step 98	COMMIT;	Waiting...	T1 commits.
Step 99		SELECT stock FROM product WHERE id = 2 FOR UPDATE; 20	Now with "SELECT FOR UPDATE", T2 reads 20
Step 100		COMMIT;	T2 commits.

Now, I want T2 to rollback 3 seconds after T2 waits for T1 as shown below:

Flow	Transaction 1 (T1)	Transaction 2 (T2)	Explanation
Step 1	BEGIN;		T1 starts.
Step 2		BEGIN;	T2 starts.
Step 3	SELECT stock FROM product WHERE id = 2 FOR UPDATE; 20		With "SELECT FOR UPDATE", T1 reads 20.
Step 4		SELECT stock FROM product WHERE id = 2 FOR UPDATE;	T2 needs to wait for T1 to commit to read stock with "SELECT FOR UPDATE".
Step 5		Waiting...	...
Step 6		Waiting...	...
Step 7		ROLLBACK;	T2 rollbacks 3 seconds after T2 waits for T1.
Step ...
Step ...
Step 98
Step 99
Step 100	COMMIT;		T1 commits.

So, how can I set the timeout of 3 seconds for SELECT FOR UPDATE in transaction in PostgreSQL?

Answer 1

Take a look at this answer: https://stackoverflow.com/a/20963803/8963723

BEGIN;
SET LOCAL lock_timeout = '3s';
SELECT ....;
COMMIT;