/** The JDBC database driver. */指定连接驱动
   public static final String DB_DRIVER = "driver";

     /** The JDBC database URL. */  连接字符串
    public static final String DB_URL = "URL";


    /** The database user name. */ 用户名
    public static final String DB_USER = "user";

    /** The database user password. */ 密码
    public static final String DB_PASSWORD = "password";

    /** The maximum number of database connections to have in the pool.  Default is 10. */ 连接池最大连接数
    public static final String DB_MAX_CONNECTIONS = "maxConnections";

    /** 
     * The maximum number of prepared statements that will be cached per connection in the pool.
     * Depending upon your JDBC Driver this may significantly help performance, or may slightly 
     * hinder performance.   
     * Default is 120, as Quartz uses over 100 unique statements. 0 disables the feature. 
     */     每个链接最多缓存多少个预编译语句
    public static final String DB_MAX_CACHED_STATEMENTS_PER_CONNECTION = "maxCachedStatementsPerConnection";

    /** 
     * The database sql query to execute every time a connection is returned 
     * to the pool to ensure that it is still valid. 
     */  验证连接是否可用的查询语句
    public static final String DB_VALIDATION_QUERY = "validationQuery";

    /** 
     * The number of seconds between tests of idle connections - only enabled
     * if the validation query property is set.  Default is 50 seconds. 
     */   多久验证空闲连接
    public static final String DB_IDLE_VALIDATION_SECONDS = "idleConnectionValidationSeconds";

    /** 
     * Whether the database sql query to validate connections should be executed every time 
     * a connection is retrieved from the pool to ensure that it is still valid.  If false,
     * then validation will occur on check-in.  Default is false. 
     */  是否每次从池中取连接时，验证连接可用性
    public static final String DB_VALIDATE_ON_CHECKOUT = "validateOnCheckout";
    
    /** Discard connections after they have been idle this many seconds.  0 disables the feature. Default is 0.*/   空闲连接超过多少秒丢弃
    private static final String DB_DISCARD_IDLE_CONNECTIONS_SECONDS = "discardIdleConnectionsSeconds"; 

    /** Default maximum number of database connections in the pool. */  最大连接数
    public static final int DEFAULT_DB_MAX_CONNECTIONS = 10;

    /** Default maximum number of database connections in the pool. */   默认每个链接缓存120个预编译语句
    public static final int DEFAULT_DB_MAX_CACHED_STATEMENTS_PER_CONNECTION = 120;