How does locking work in INSERT..ON DUPLICATE KEY UPDATE statements?

Question

I am encountering deadlocks while trying to update multiple rows (a batch) using INSERT..ON DUPLICATE KEY UPDATE. Does MySQL lock all the rows in one batch or does it lock only the row it is updating at a point of time?

Answer 1

since mysql 5.7, it will acquire GAP lock if the value(has unique index) does not exist.

INSERT INTO ... SELECT ... ON DUPLICATE KEY UPDATE and LOAD DATA CONCURRENT REPLACE took too weak a lock, leading to the possibility of concurrent SELECT statements returning inconsistent results. (Bug #38046, Bug #11749055)

refer this link for detail:

https://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-0.html

Answer 2

This would depend on the Storage Engine.

• MyISAM : Table-level locks are performed. Consequently, all rows are locked.

• InnoDB : Row-level locks are employed. Since InnoDB is transactional, all rows are locked implcitly. Those locks would be visible when you run SHOW ENGINE INNODB STATUS\G. If you want to manually lock those rows beforehand to prevent sharing, you could run SELECT ... FOR UPDATE.