Connection pooling can effectively reduce the overhead of frequently creating and destroying connections and avoid database connection exhaustion. 1. Each new connection is created to consume resources and time. Under high concurrency, it will lead to increased latency, increased load and exceeded the maximum number of connections limit; 2. The connection pool pre-creates connections when the application starts and reuses them after use to improve efficiency and control resource consumption; 3. The selection needs to consider performance (such as HikariCP), feature richness (such as Druid), integration, community support, etc.; 4. The core configuration includes the minimum number of idle connections (5~10), maximum number of connections (not exceeding 80% of the database limit), connection timeout (within 30s), idle timeout (within a few minutes to ten minutes), etc.; 5. Common misunderstanding is that the maximum number of connections is set too large, and parameters should be adjusted in combination with pressure measurement; 6. When using it, release connections, monitor usage, cooperate with database configuration optimization, and unify multi-node configuration to maintain consistency.

Connection pooling is one of the key means to improve the performance of MySQL applications, especially in high concurrency scenarios. Properly configuring the connection pool can effectively reduce the overhead of frequently creating and destroying connections, while avoiding the problem of database connection exhaustion.

Why do I need a connection pool?

Every time MySQL establishes a new connection, it requires a certain amount of resources and time, including TCP handshake, authentication and other steps. In applications with high concurrency, frequent opening and closing of connections can lead to:

• Response delay increases
• Database server load increases
• Max connection limit may be exceeded (max_connections)

The purpose of the connection pool is to create a certain number of connections in advance when the application is started, and not close it immediately after use is completed, but put it back into the pool for subsequent request reuse, thereby improving efficiency and controlling resource consumption.

How to choose the right connection pool component?

Commonly used Java applications include HikariCP, C3P0, Druid, etc.; SQLAlchemy's connection pool or DBUtils can be used in Python; the Go language standard library database/sql itself also supports the connection pooling mechanism. The following points are mainly considered when selecting the model:

• Performance: HikariCP is known for its lightweight and efficientness, suitable for most scenarios
• Feature richness: Druid provides monitoring panel, slow log query and other functions
• Easy to integrate: good compatibility with the current framework
• Community activity and support

For example, in Spring Boot projects, HikariCP is used by default, which usually only requires a few simple configurations to enable.

Key configuration parameters and suggestions

The specific parameters of each connection pool component may be slightly different, but the core configuration ideas are basically the same:

• Minimum number of idle connections (minIdle/minIdle) : Keep a certain number of idle connections for quick response to burst requests. Generally, set to 5~10
• MaximumPoolSize/maxActive : Set according to the maximum number of connections allowed by the database. For example, when MySQL sets max_connections=200 , it is best if all applications add up to no more than 80% of this value.
• ConnectionTimeout: Set the maximum time the client waits for connection. It is recommended to avoid long-term blockage of requests.
• Idle Timeout : How long will the connection be recycled after it is idle in the pool? It is recommended to set it to several minutes to more than ten minutes.
• ValidationQuery : Some connection pools require SQL statements to verify connection validity, such as SELECT 1 , but modern pools such as HikariCP are automatically processed and do not require additional configuration.

A common misunderstanding is to set the maximum number of connections too large, which will result in overwhelming the database. It is recommended to observe the actual performance in combination with the pressure measurement tool and then make adjustments.

Tips to avoid common problems

• Don't forget to release the connection : make sure that the close() or release method is called after each operation of the database, otherwise the connection will not return to the pool.
• Monitor connection usage : Regularly check the current connection pool usage rate, waiting number and other indicators to discover potential bottlenecks in a timely manner
• Cooperate with database configuration optimization : For example, appropriately increase wait_timeout and interactive_timeout to avoid the connection being actively disconnected by MySQL

If your application is deployed on multiple nodes, remember to configure the connection pool to prevent a machine from occupying too many connection resources.

Basically that's it. Configuring connection pooling is not a one-time task. As business growth and access patterns change, parameters need to be constantly reviewed and adjusted.

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