Mysql update rowlock

The X lock of our first query is blocking it. OK, let's rollback the queries, and see what happens if we have the first query update the second row, and the second query update the first row?

Does that work? Because SQL still has no way of knowing how many rows match the predicate. So the first query takes its update lock on slot 0, sees that it doesn't have to update it, takes its update lock on slot 1, sees the correct value for i , takes its exclusive lock, and waits for us to commit. The query 2 comes along, takes the update lock on slot 0, sees the value it wants, takes its exclusive lock, updates the value, and then tries to take an update lock on slot 1 , because that might also have the value it wants.

You'll also see "intent locks" on the next "level" up, i. The operation is letting the rest of the engine know that it might want to escalate the lock to the page level at some point in the future. But that's not a factor here. Page locking is not causing the issue. Solution in this case? Add an index on column i. In this case, that's probably the primary key. You can then do the updates in either order. Asking for row locking in this case makes no difference, because SQL doesn't know how many rows match the predicate.

But even if you try to force a row lock in some situation, and even with a primary key or appropriate index, SQL can still choose to escalate the lock type, because it can be way more efficient to lock a whole page, or a whole table, than to lock and unlock individual rows.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. A similar situation occurs if the table already contains a row with key value 1 and three sessions perform the following operations in order:. When session 1 commits, it releases its exclusive lock on the row and the queued shared lock requests for sessions 2 and 3 are granted.

An exclusive index-record lock is taken for a duplicate primary key value. An exclusive next-key lock is taken for a duplicate unique key value.

Otherwise, an exclusive next-key lock is placed on the row to be replaced. Otherwise, InnoDB sets shared next-key locks on rows from S. InnoDB has to set locks in the latter case: During roll-forward recovery using a statement-based binary log, every SQL statement must be executed in exactly the same way it was done originally. FROM s For more information, See Section If a FOREIGN KEY constraint is defined on a table, any insert, update, or delete that requires the constraint condition to be checked sets shared record-level locks on the records that it looks at to check the constraint.

InnoDB also sets these locks in the case where the constraint fails. Otherwise, InnoDB 's automatic deadlock detection cannot detect deadlocks where such table locks are involved. Also, because in this case the higher MySQL layer does not know about row-level locks, it is possible to get a table lock on a table where another session currently has row-level locks.

However, this does not endanger transaction integrity, as discussed in Section In MySQL 8. All InnoDB locks held by a transaction are released when the transaction is committed or aborted. Testing and Benchmarking with InnoDB. InnoDB Multi-Versioning. Creating Tables Externally. Clustered and Secondary Indexes.

The System Tablespace. File-Per-Table Tablespaces. Improve this question. Elsayed Elsayed 9 9 bronze badges. How much of a table are you updating? One row or more? How large is each row?

Are you updating rows by primary key or by querying other columns? Is the estimated row count accurate? Are you using any hints? What about the escalation policy on the table? Delayed write? What is your isolation level? Any cascade foreign keys? Does the lock actually block anyone? Jonathan's many questions are important, but most are not relevant to the rather narrow Question at hand. If you are doing an update, and Update Lock is generated.

That update lock flags the rows that it will need to update first. Then once the update starts the lock is applied, and that could be a Row Lock. If more than twenty five row locks are needed, that might be escalated into a page lock, and so on.

Thank you Phil, that's why I said it could be a Row Lock. I honestly don't like changing the behaviour or forcing the engine to do something that it doesn't like, and this is one of them and for the reason you mentioned. Not quite solid on this topic yet. After reading your posts, It seems to me that there is no need to actually type the work rowlock. Am I right? In my personal opinion, you shouldn't.