Hi Sanja, and Igor, (resending with Igor on CC) I noticed a FOR UPDATE behavior change in 10.3-MDEV-11953 In 10.3 I run this script in a client session: CREATE OR REPLACE TABLE t1 (a INT NOT NULL PRIMARY KEY); CREATE OR REPLACE TABLE t2 (a INT NOT NULL PRIMARY KEY); INSERT INTO t1 VALUES (1); INSERT INTO t2 VALUES (2); BEGIN; SELECT * FROM t1 UNION SELECT * FROM t2 FOR UPDATE; Notice no COMMIT yet! It returns this result: +---+ | a | +---+ | 1 | | 2 | +---+ Now I open a new console, start a new client session and run this script: BEGIN; SELECT * FROM t2 FOR UPDATE; The second session gets locked, as expected. Now I return to the first console and run "COMMIT;". The second console gets unlocked and returns +---+ | a | +---+ | 2 | +---+ Now if I do the same in 10.3-MDEV-11953, the second session does not get locked, it returns the result immediately, even before I typed "COMMIT;" in the first session. Note, if in 10.3-MDEV-11953 I start a transaction with a simpler query (without UNION) in the first session: BEGIN; SELECT * FROM t2 FOR UPDATE; and run the same script in the second session BEGIN; SELECT * FROM t2 FOR UPDATE; then the second session gets locked as expected. Is this behavior change expected? Thanks!