连接串不同则创建不同的池子，Max Pool Size=200;Min Pool Size=5 相同连接串的最大最小值，不同连接串则分别有自己的最大最小值。
Max Pool Size默认100，Min Pool Size默认0。
https://msdn.microsoft.com/zh-cn/library/8xx3tyca(v=vs.80).aspx
https://msdn.microsoft.com/zh-cn/library/system.data.sqlclient.sqlconnection.connectionstring(VS.80).aspx
池的创建和分配
在初次打开连接时，将根据完全匹配算法创建连接池，该算法将池与连接中的连接字符串关联。每个连接池与不同的连接字符串关联。打开新连接时，如果连接字符串并非与现有池完全匹配，将创建一个新池。按进程、按应用程序域、按连接字符串以及（在使用集成的安全性时）按 Windows 标识来建立池连接。
Timeout 时间已到。在操作完成之前超时时间已过或服务器未响应。
Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.
http://www.dotnetspark.com/links/18280-timeout-when-calling-sqldataadapterfilldataset.aspx
http://stackoverflow.com/questions/14993309/what-is-snireadsyncoverasync-and-why-would-it-take-a-long-time-to-complete
System.Data.SqlClient.SqlException (0x80131904): Timeout expired.
The timeout period elapsed prior to completion of the operation or the server is not responding.
---> System.ComponentModel.Win32Exception (0x80004005): 等待的操作过时。
at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
at System.Data.SqlClient.TdsParserStateObject.ReadSniError(TdsParserStateObject stateObj, UInt32 error)
at System.Data.SqlClient.TdsParserStateObject.ReadSniSyncOverAsync()
at System.Data.SqlClient.TdsParserStateObject.TryReadNetworkPacket()
at System.Data.SqlClient.TdsParserStateObject.TryPrepareBuffer()
at System.Data.SqlClient.TdsParserStateObject.TryReadByte(Byte& value)
at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
at System.Data.SqlClient.SqlDataReader.TryConsumeMetaData()
at System.Data.SqlClient.SqlDataReader.get_MetaData()
at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)
at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, SqlDataReader ds)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
at System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
at System.Data.Common.DbCommand.System.Data.IDbCommand.ExecuteReader(CommandBehavior behavior)
at System.Data.Common.DbDataAdapter.FillInternal(DataSet dataset, DataTable[] datatables, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior)
at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior)
at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet)
at DNA.OpenPlatform.Common.SqlHelper.ExecuteDataset(String connectionString, CommandType commandType, String commandText, SqlParameter[] commandParameters)