这是一个将MaxIdleConnections添加到DBStats的提案。
目前，DBStats导出以下指标：

type DBStats struct {
    MaxOpenConnections int // Maximum number of open connections to the database.

    // Pool Status
    OpenConnections int // The number of established connections both in use and idle.
    InUse           int // The number of connections currently in use.
    Idle            int // The number of idle connections.

    // Counters
    WaitCount         int64         // The total number of connections waited for.
    WaitDuration      time.Duration // The total time blocked waiting for a new connection.
    MaxIdleClosed     int64         // The total number of connections closed due to SetMaxIdleConns.
    MaxIdleTimeClosed int64         // The total number of connections closed due to SetConnMaxIdleTime.
    MaxLifetimeClosed int64         // The total number of connections closed due to SetConnMaxLifetime.
}

我们遇到了这样的问题：我们的应用程序配置了MaxOpenConnections不等于MaxIdleConnections,导致大量连接在数据库之间切换。
虽然MaxOpenConnections已经在统计数据中可用，但缺少MaxIdleConnections,使得跟踪受影响的应用程序变得困难。