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🗣 Wd提问: MySQL wait_timeout

🤖 Ai回答:
In MySQL, the `wait_timeout` system variable controls how long a connection to the MySQL server can remain idle (i.e., without any activity) before it is automatically closed by the server.

✅ What is `wait_timeout`?

Default value: Usually 8 hours (28,800 seconds), but may vary depending on MySQL version and configuration.
Applies to: All client connections that are idle (no queries, no data transfer).
Does NOT apply to: Active connections performing queries or transactions.
Scope: Global and Session level — can be set globally for all connections or per session.

⚙️ How to Check Current Value

sql
SHOW VARIABLES LIKE 'wait_timeout';

Example output:

+++
| Variable_name | Value |
+++
| wait_timeout | 28800 |
+++

🛠️ How to Set `wait_timeout`

1、Set Globally (affects all new connections)

sql
SET GLOBAL wait_timeout = 600; 10 minutes

💡 Note: This requires SUPER privilege.

2、Set Per Session (only affects current session)

sql
SET SESSION wait_timeout = 600;

3、In my.cnf / my.ini (for permanent change)

Add or modify under `[mysqld]` section:

ini
[mysqld]
wait_timeout = 600

Then restart MySQL service for changes to take effect.

🔄 Related Variable: `interactive_timeout`

Similar to `wait_timeout`, but applies to interactive clients (like mysql CLI) instead of non-interactive ones (like PHP, Python scripts, etc.).
Often set higher for interactive sessions (e.g., 28800).

❗ Important Notes

Connection loss: If a client is idle longer than `wait_timeout`, it will lose its connection、The client must reconnect if needed.
Application impact: Long-running applications may need to handle reconnection logic if they’re affected.
Security: Shorter timeouts help reduce resource usage and potential security risks from idle connections.
Performance: Too short a timeout may cause legitimate long-running operations to disconnect prematurely.

🔍 Example Scenario

You have an application that connects to MySQL via a script that runs every 5 minutes、If `wait_timeout` is 28800 (8 hours), your script won’t be affected、But if you set it to 300 (5 minutes), the connection might close between script runs — so your app needs to handle reconnecting.

✅ Best Practices

Set `wait_timeout` based on your application’s behavior (e.g., 60–300 seconds for web apps).
Use `interactive_timeout` for interactive sessions if different behavior is needed.
Always test changes in staging before production.
Consider using connection pooling (e.g., with libraries like `mysql-connector-python`, `Druid`, or `HikariCP`) to manage connections efficiently.

🧪 Test Connection Timeout

You can simulate an idle connection by running this:

sql
Connect to MySQL
Do nothing for 10 minutes
Then check if connection still alive
SELECT CONNECTION_ID();

If connection was closed, you’ll get an error when trying to query.

Let me know if you want to configure `wait_timeout` for specific users, or troubleshoot connection drops!

Ai作答

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