提供一篇关于sqlconnection连接池详细，有需要的朋友参考一下。
物理连接建立时，需要做和服务器握手，解析连接字符串，授权，约束的检查等等操作，而物理连接建立后，这些操作就不会去做了。这些操作是需要一定的时间的。所以很多人喜欢用一个静态对象存储 sqlconnection 来始终保持物理连接，但采用静态对象时，多线程访问会带来一些问题，实际上，我们完全不需要这么做，因为 sqlconnection 默认打开了连接池功能，当程序 执行  sqlconnection.close 后，物理连接并不会被立即释放，所以这才出现当循环执行 open操作时，执行时间几乎为0.
下面我们先看一下不打开连接池时，循环执行 sqlconnection.open 的耗时
代码如下 复制代码
       public static void openwithoutpooling()
        {
            string connectionstring =
                data source=192.168.10.2; initial catalog=news; integrated security=true;pooling=false;;
            stopwatch sw = new stopwatch();
            sw.start();
            using (sqlconnection conn =
                new sqlconnection(connectionstring))
            {
                conn.open();
            }
            sw.stop();
            console.writeline(without pooling, first connection elaed {0} ms, sw.elapsedmilliseconds);
            sw.reset();
            sw.start();
            for (int i = 0; i             {
                using (sqlconnection conn = new sqlconnection(connectionstring))
                {
                    conn.open();
                }
            }
            sw.stop();
            console.writeline(without pooling, average connection elapsed {0} ms, sw.elapsedmilliseconds / 100);
        }
sqlconnection 默认是打开连接池的，如果要强制关闭，我们需要在连接字符串中加入 pooling=false
调用程序如下：
 代码如下 复制代码
                test.sqlconnectiontest.openwithoutpooling();
                console.writeline(waiting for 10s);
                system.threading.thread.sleep(10 * 1000);
                test.sqlconnectiontest.openwithoutpooling();
                console.writeline(waiting for 600s);
                system.threading.thread.sleep(600 * 1000);
                test.sqlconnectiontest.openwithoutpooling();
下面是测试结果 
without pooling, first connection elapsed 13 ms
without pooling, average connection elapsed 5 ms
wating for 10s
without pooling, first connection elapsed 6 ms
without pooling, average connection elapsed 4 ms
wating for 600s
without pooling, first connection elapsed 7 ms
without pooling, average connection elapsed 4 ms
从这个测试结果看，关闭连接池后，平均每次连接大概要耗时4个毫秒左右，这个就是建立物理连接的平均耗时。
下面再看默认情况下的测试代码
代码如下 复制代码
  public static void openwithpooling()
        {
            string connectionstring =
                data source=192.168.10.2; initial catalog=news; integrated security=true;;
stopwatch sw = new stopwatch();
            sw.start();
            using (sqlconnection conn =
                new sqlconnection(connectionstring))
            {
                conn.open();
            }
            sw.stop();
            console.writeline(with pooling, first connection elapsed {0} ms, sw.elapsedmilliseconds);
            sw.reset();
            sw.start();
            for (int i = 0; i             {
                using (sqlconnection conn = new sqlconnection(connectionstring))
                {
                    conn.open();
                }
            }
            sw.stop();
            console.writeline(with pooling, average connection elapsed {0} ms, sw.elapsedmilliseconds / 100);
        }
调用代码
test.sqlconnectiontest.openwithpooling();
                console.writeline(waiting for 10s);
                system.threading.thread.sleep(10 * 1000);
                test.sqlconnectiontest.openwithpooling();
                console.writeline(waiting for 600s);
                system.threading.thread.sleep(600 * 1000);
                test.sqlconnectiontest.openwithpooling();
测试结果
with pooling, first connection elapsed 119 ms
with pooling, average connection elapsed 0 ms
waiting for 10s
with pooling, first connection elapsed 0 ms
with pooling, average connection elapsed 0 ms
waiting for 600s
with pooling, first connection elapsed 6 ms
with pooling, average connection elapsed 0 ms
这个测试结果看，第一次耗时是119ms，这是因为我在测试代码中，首先运行的是这个测试过程，119 ms 是程序第一次启动时的首次连接耗时，这个耗时可能不光包括连接的时间，还有 ado.net 自己初始化的用时，所以这个用时可以不管。10秒以后在执行这个测试过程，首次执行的时间变成了0ms，这说明连接池机制发生了作用，sqlconnection close 后，物理连接并没有被关闭，所以10秒后再执行，连接几乎没有用时间。
但我们发现一个有趣的现象，10分钟后，首次连接时间变成了6ms，这个和前面不打开连接池的测试用时几乎一样，也就是说10分钟后，物理连接被关闭了，又重新打开了一个物理连接。这个现象是因为连接池有个超时时间，默认情况下应该在5-10分钟之间，如果在此期间没有任何的连接操作，物理连接就会被关闭。那么我们有没有办法始终保持物理连接呢？方法是有的。
连接池设置中有一个最小连接池大小，默认为0，我们把它设置为大于0的值就可以保持若干物理连接始终不释放了。看代码
代码如下 复制代码
public static void openwithpooling(int minpoolsize)
        {
            string connectionstring =
                string.format(data source=192.168.10.2; initial catalog=news; integrated security=true;min pool size={0},
                    minpoolsize);
            stopwatch sw = new stopwatch();
            sw.start();
            using (sqlconnection conn =
                new sqlconnection(connectionstring))
            {
                conn.open();
            }
            sw.stop();
            console.writeline(with pooling min pool size={0}, first connection elapsed {1} ms,
                minpoolsize, sw.elapsedmilliseconds);
            sw.reset();
            sw.start();
            for (int i = 0; i             {
                using (sqlconnection conn = new sqlconnection(connectionstring))
                {
                    conn.open();
                }
            }
            sw.stop();
            console.writeline(with pooling min pool size={0}, average connection elapsed {1} ms,
                minpoolsize, sw.elapsedmilliseconds / 100);
        }
其实只要在连接字符串中加入一个 min pool size=n 就可以了。
调用代码
 代码如下 复制代码
test.sqlconnectiontest.openwithpooling(1);
                console.writeline(waiting for 10s);
                system.threading.thread.sleep(10 * 1000);
                test.sqlconnectiontest.openwithpooling(1);
                console.writeline(waiting for 600s);
                system.threading.thread.sleep(600 * 1000);
                test.sqlconnectiontest.openwithpooling(1);
with pooling min pool size=1, first connection elapsed 5 ms
with pooling min pool size=1, average connection elapsed 0 ms
waiting for 10s
with pooling min pool size=1, first connection elapsed 0 ms
with pooling min pool size=1, average connection elapsed 0 ms
waiting for 600s
with pooling min pool size=1, first connection elapsed 0 ms
with pooling min pool size=1, average connection elapsed 0 ms
我们可以看到当 min pool size = 1  时，除了首次连接用时5ms以外，即便过了10分钟，用时还是0ms，物理连接没有被关闭。