How to use distributed locks to control concurrent access in MySQL?

How to use distributed locks to control concurrent access in MySQL?

In database systems, high concurrent access is a common problem, and distributed locks are one of the common solutions. This article will introduce how to use distributed locks in MySQL to control concurrent access and provide corresponding code examples.

1. Principle
Distributed locks can be used to protect shared resources to ensure that only one thread can access the resource at the same time. In MySQL, distributed locks can be implemented in the following ways:

• Create a table named lock_table to store the status of the lock. The table needs to contain at least the following fields: lock name, lock holder, lock status, etc.
• Access and modify lock_table by using transactions and row-level locks.

2. Implementation steps
The following are the steps to use distributed locks in MySQL:

Step 1: Create lock_table
First, create a table named lock_table Table used to store lock status. The table is defined as follows:

CREATE TABLE lock_table (
id INT NOT NULL AUTO_INCREMENT,
lock_name VARCHAR(64) NOT NULL,
lock_holder VARCHAR(64) DEFAULT NULL,
status INT DEFAULT '0',
created_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (id),
UNIQUE KEY lock_name (lock_name)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

Step 2: Obtain distributed lock
The following is a code example to obtain a distributed lock:

START TRANSACTION;

SELECT * FROM lock_table WHERE lock_name = 'my_lock' FOR UPDATE;

-- Determine whether other threads already hold the lock
SELECT * FROM lock_table WHERE lock_name = 'my_lock' AND status = 1;

-- If no other thread holds the lock If you have a lock, you can set yourself as the holder of the lock and set the lock status to 1
INSERT INTO lock_table (lock_name, lock_holder, status) VALUES ('my_lock', 'thread_id', 1);

COMMIT;

Step 3: Release the distributed lock
When the thread completes the operation of the shared resource, the distributed lock should be released in time. The following is a code example to release a distributed lock:

START TRANSACTION;

SELECT * FROM lock_table WHERE lock_name = 'my_lock' FOR UPDATE;

-- Determine whether the current thread Holding lock
SELECT * FROM lock_table WHERE lock_name = 'my_lock' AND lock_holder = 'thread_id';

-- If the current thread holds the lock, then set the lock holder and status to null and 0
UPDATE lock_table SET lock_holder = NULL, status = 0 WHERE lock_name = 'my_lock' AND lock_holder = 'thread_id';

COMMIT;

3. Notes
In When using distributed locks, you need to pay attention to the following points:

• Try to avoid long transactions: Long transactions will occupy lock resources and cause other threads to wait too long. Therefore, the length of the transaction should be minimized and operations on shared resources should be completed as quickly as possible.
• Avoid deadlock: Deadlock refers to a situation where two or more transactions are waiting for each other to release lock resources, resulting in the inability to continue. In order to avoid the occurrence of deadlock, you should pay attention to the order of lock acquisition and release when using distributed locks.
• Consider lock management in a distributed environment: In a distributed environment, different database instances may have problems such as network delays, so the management and scheduling of distributed locks need to be considered. You can use distributed lock services or other distributed coordination tools to manage the allocation and release of lock resources.

4. Summary
This article introduces how to use distributed locks to control concurrent access in MySQL, and provides corresponding code examples. Distributed locks are a commonly used way to solve high concurrent access problems, but precautions need to be taken when using them to avoid long transactions and deadlocks. In a distributed environment, lock management and scheduling also need to be considered.

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