Comparative analysis of the functions and advantages and disadvantages of MySQL table locks, page locks and row locks

In MySQL, different lock mechanisms (table locks, page locks, row locks) directly affect the concurrency performance and data consistency of the database. Here is a detailed comparison of them:

1. Table Lock

effect: Lock the entire table, and other sessions cannot modify or read data in the table (specific behavior depends on the lock type, such as a shared lock or an exclusive lock).

Applicable scenarios：

• MyISAM storage engine (using table locks by default).
• Batch data import/export operation.
• DDL statements that require full table scanning (such asALTER TABLE）。

advantage：

• Simple implementation: The locking logic is direct and the system overhead is small.
• No deadlock risk: There will be no deadlock under the single lock mechanism.
• Quick locking: Only table-level locks need to be maintained, and the operation is efficient.

shortcoming：

• Poor concurrency: Only one session is allowed to write at the same time.
• High competitive risk: Frequent writing operations will cause a large number of session blocking.
• Coarse particle size: Even if a small amount of data is modified, the entire table will be locked.

2. Page Lock

effect: Lock the data page (the page is the smallest unit of data managed by the storage engine, usually 16KB), and multiple lines of data within the same page will be locked at the same time.

Applicable scenarios：

• Older versions of InnoDB (modern InnoDB has deprecated page locks, mainly using row locks).
• Scenarios where lock granularity and system overhead need to be balanced (less common).

Advantages：

• Medium particle size: Between table locks and row locks, reducing the number of locks.
• Moderate overhead: It is simpler than row lock management and has better concurrency than table locks.

shortcoming：

• Potential conflict: Modifications of different lines within the same page will still block each other.
• Insufficient flexibility: Can't control exactly like a line lock.
• It has gradually been eliminated: Modern storage engines (such as InnoDB) have turned to row locks.

3. Row Lock

effect: Only one row of data is locked, and other rows can be accessed concurrently.

Applicable scenarios：

• InnoDB storage engine (by default, line locks are used).
• High concurrent transaction environment (such as e-commerce, financial systems).
• Scenarios where data modification is required are carefully controlled.

advantage：

• High concurrency: Allow multiple transactions to modify different rows at the same time.
• Precise control: Only lock the target data to reduce blockage.
• Support complex transactions: Combined with MVCC, it can realize repeated reading and prevent phantom reading.

shortcoming：

• Large system overhead: It requires maintenance of a large amount of lock information, consuming memory and CPU.
• Deadlock risk: Multi-transaction competition for line locks may lead to deadlocks and additional detection mechanisms are required.
• Lock upgrade possible: When there are too many row locks, it may be upgraded to a table lock (such as full table update).

Comparison table

Select a suggestion

• Read more and write less: Table lock (MyISAM) or row lock (InnoDB) are both possible, and transaction needs are preferred.
• High concurrent write: Required line lock (InnoDB) to avoid lock competition.
• Batch operation: Use table locks (such asLOCK TABLES ... WRITE) Improve efficiency.
• Financial transactions: Row lock + MVCC, combined with transaction isolation level (if you can read it repeatedly).

Sample code

Explicit table lock（MyISAM）：

LOCK TABLES orders WRITE;
-- Perform batch update operations
UNLOCK TABLES;

Use of line lock（InnoDB）：

BEGIN;
SELECT * FROM products WHERE id = 100 FOR UPDATE; -- Exclusive lock for additional row level
UPDATE products SET stock = stock - 1 WHERE id = 100;
COMMIT;

Things to note

Deadlock processing：

• useSHOW ENGINE INNODB STATUSAnalyze deadlock logs.
• Set a reasonable lock waiting timeout time (innodb_lock_wait_timeout）。

Lock monitoring：

• View lock information:SELECT * FROM information_schema.INNODB_LOCKS;
• Monitor lock waiting:SELECT * FROM information_schema.INNODB_LOCK_WAITS;

Optimization suggestions：

• Avoid long transactions and reduce lock holding time.
• Hotspot data is processed by queue or asynchronously updated.

Through the reasonable selection of lock mechanism, the concurrency performance and data consistency of MySQL can be significantly improved.

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