How to Fix mysql: Error 1040: Too many connections in Go

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Go raises the “Error 1040: Too many connections” in MySQL occurs when the maximum number of concurrent connections to the MySQL server has been reached. By default, MySQL allows up to 151 concurrent connections.

In a Go application, this error might occur if your application creates many connections without closing them or uses a connection pool with an improperly configured maximum limit.

To fix this error, consider the following steps:

Fix 1: Close connections

Ensure that you are closing each connection after it is no longer needed. Use the defer statement to ensure connections are correctly closed.

package main

import (
  "database/sql"
  "log"
)

func main() {
  conn, err := sql.Open("mysql", "user:password@tcp(localhost:3306)/dbname")
  if err != nil {
    log.Fatal(err)
  }
  defer conn.Close()
}

Fix 2: Use the connection pooling

Go’s database/SQL package provides a built-in connection pool. First, configure the connection pool’s maximum number of connections by setting the SetMaxOpenConns property:

conn.SetMaxOpenConns(50)

Adjust the value based on your application’s needs and the MySQL server’s capacity.

Fix 3: Increase MySQL’s max_connections

If your application genuinely requires a higher number of concurrent connections, consider increasing the max_connections value in the MySQL configuration file (my.cnf or my.ini) under the [mysqld] section:

[mysqld]

max_connections = 300

After making the changes, restart the MySQL server for the new configuration to take effect.

Fix 4: Monitor connections

Keep an eye on how many connections your application makes to the MySQL server. Use the following SQL query to check the current number of connections:

SHOW STATUS WHERE Variable_name = 'Threads_connected';

Fix 5: Optimize queries and application logic

Review your application’s logic and queries to ensure they are optimized and not causing unnecessary connections. For example, if your application has long-running queries, consider optimizing them to reduce the load on the MySQL server.

Remember that increasing the number of concurrent connections consumes more server resources, so finding a balance between the application’s requirements and the server’s capacity is essential.

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