Why locking read ignore isolation level?

Example:

SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;  START TRANSACTION;  SELECT * FROM t1; // to "create shapshot". For simplicity t1 contains 1 row 1 column which contains value 1.  // another transaction updates this row and change 1 to 2 and commits.  SELECT * FROM t1; // we see no changes. As expected in repeatable read.  SELECT * FROM t1 FOR UPDATE; // i see change row. Why?  

The problem i cant find explanation to such behaviour. Why locking read ignore isolation level?

https://stackoverflow.com/questions/67393916/why-locking-read-ignore-isolation-level May 05, 2021 at 08:58AM