MySQL connection pool is a "connection repository" that is used to efficiently manage database connections and avoid resource waste and performance bottlenecks. Its core function is to create connections in advance for programs to "borrow and return" to reduce the overhead of frequent connection establishment and destruction. Common configuration parameters include: 1. Max_connections; 2. Idle connection timeout time (idle_timeout); 3. Wait timeout time (wait_timeout); 4. Initial connection number (initial_size). When selecting a connection pool library, you can consider HikariCP, Druid, C3P0, etc. The usage steps include introducing dependencies, configuring parameters, initializing, obtaining and returning connections. Common problems include connection leakage, unreasonable settings for maximum connections, disconnection of idle connections, and unclosed connection pools, etc. The problem needs to be configured reasonably, monitored and promptly investigated to ensure performance and stability under high concurrency.

MySQL connection pooling and management, to put it bluntly, is how to efficiently use database connections to avoid resource waste and performance bottlenecks. Many people start writing programs, and they just disconnect after using one connection. It seems to be fine, but once it is concurrent, the efficiency will be greatly reduced. Therefore, the function of the connection pool is to prepare some connections in advance so that the program can "borrow" and "return", rather than re-establishing the connection every time.

What is MySQL connection pool?

A connection pool is actually a "connection repository". When your program needs to connect to the database, it does not create a new connection every time, but "borrow" one from the pool. Return it after use, instead of disconnecting it directly. The benefit of this is to reduce the overhead of frequently creating and destroying connections and improve response speed.

For example, if you write a web application, you have to connect to the database every time you make a request. If each request creates a new connection, the database may not be able to withstand the number of connections when the concurrency is large, and even the number of connections is full. After using the connection pool, the maximum number of connections can be controlled to avoid avalanches.

What are the common configuration parameters for connection pools?

The connection pool is not used casually, it must be configured according to the actual situation. You need to understand several key parameters:

• Max_connections : How many connections are available in the pool at most. If it is set too small, it may not be enough; if it is set too large, it will waste resources.
• Idle connection timeout (idle_timeout) : Release if the connection is not used for too long to avoid occupancy of resources.
• Wait timeout (wait_timeout) : When the connection pool is full, how long will other requests wait at most.
• Initialize connections (initial_size) : prepares how many connections to avoid lag in the first request.

These parameters are not fixed, they depend on your business volume and database affordability. For example, in high concurrency systems, max_connections can set a high point, but it cannot exceed the maximum number of connections allowed by the database.

How to choose and use the connection pool library?

There are many mainstream connection pool libraries now, such as HikariCP, C3P0, and Druid in Java; Python has the connection pool that comes with SQLAlchemy; Go and Node.js also have their own implementations. When choosing, it mainly depends on performance, stability and monitoring functions.

For example, HikariCP is used a lot in Java projects because of its good performance and simple configuration. In addition to the connection pool function, Druid also has a monitoring panel, which can view connection usage and is suitable for projects that require operation and maintenance support.

The steps to use a connection pool are generally:

• Introduce dependencies (such as Maven, npm, etc.)
• Configure database address, account password, connection pool parameters
• Initialize the connection pool
• Each operation gets the connection from the pool and returns it after the operation

Be careful not to use up the connection and not return it, otherwise the pool will be "empty", causing subsequent requests to be stuck.

Frequently Asked Questions and Notes

If the connection pool is used well, it will improve efficiency, but if it is not used well, it will also cause problems. The following points are easily overlooked:

• Connection leak : If the connection is used, the pool will be slowly hollowed out. Remember to close every time you run out, or use try-with-resources.
• The maximum number of connections is unreasonable : If the number of connections allowed by the database is smaller than the connection pool, it will cause the connection to wait or even denial of service.
• The connection is too idle for too long and is automatically disconnected by the database : At this time, the connection in the connection pool may have expired, and a test statement or automatic reconnection mechanism needs to be configured.
• The connection pool is not closed, resulting in memory leaks : remember to close the connection pool at the end of the program and release resources.

These problems are easy to encounter during development and online, especially when the test environment is not a problem, but if the production environment is released simultaneously, problems will arise.

Basically that's it. Connection pooling is not complicated, but not being used properly will affect performance and stability, especially when the concurrency volume is high. Only by rationally configuring, monitoring usage status, and promptly troubleshooting problems can the database be connected to this "water pipe" and transmitting data smoothly.

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