SqlConnection 的连接池机制解析

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

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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

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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

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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

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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。