Що таке GAP Locks у MySQL?
What is a gap lock in MySQL?
Gap Locks. A gap lock is a lock on a gap between index records, or a lock on the gap before the first or after the last index record. For example, SELECT c1 FROM t WHERE c1 BETWEEN 10 and 20 FOR UPDATE; prevents other transactions from inserting a value of 15 into column t.
What are locks in MySQL?
A MySQL Locks is nothing but a flag that can be assigned to a table to alter its properties. MySQL allows a table lock that can be assigned by a client-server to prevent other sessions from being able to access the same table during a specific time frame.
How to avoid system lock in MySQL?
MySQL Preventing Table Locking Performance Optimization
- SET TRANSACTION ISOLATION LEVEL READ COMMITTED; START TRANSACTION; — Your SQL statements here COMMIT;
- START TRANSACTION; UPDATE accounts SET balance = balance – 100 WHERE account_id = 1; UPDATE accounts SET balance = balance + 100 WHERE account_id = 2; COMMIT;
What is the difference between gap lock and next key lock?
Gap locks prevent this by locking the “gaps” where new rows might be inserted. Next-Key Locks: It's a combination of a record lock on an index record and a gap lock on the gap before that index record. It's used to ensure that ranges of rows are locked, preventing insertions in that range.
A gap lock is a lock on a gap between index records, or a lock on the gap before the first or after the last index record. For example, SELECT c1 FROM t WHERE …
gap lock — блокировка промежутка между, до или после индексной записи; next-key lock — блокировка записи индекса и промежутка перед ней.
In InnoDB, a gap lock isn’t about locking a row that doesn’t exist — it locks the “gap,” or the space where the row would be if it existed. This …