Timeout expired. The timeout period elapsed prior to completion of the operation or the server...

問題：

最近程序總會拋出如下異常：

An exception of type'System.Data.SqlClient.SqlException' occurred and was caught.

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Type :System.Data.SqlClient.SqlException, System.Data, Version=4.0.0.0,Culture=neutral, PublicKeyToken=b77a5c561934e089

 Message : Timeoutexpired.  The timeout period elapsedprior to completion of the operation or the server is not responding.

Source : .Net SqlClient Data Provider......

......Database.ExecuteReader(DbCommandcommand)......

讀取數據超時。

然後就去看了下DataBase裏對應的tables，發現table的結構簡單，但是數據量很大，有幾十萬上百萬條。再看一下有沒有建Indexes/Keys，發現沒有，恍然大悟。

解決方法：

根據表的結構，建立了Indexes/Keys下的 Unique key，類似如下：

ALTER TABLE [dbo].[ZData]
 add  CONSTRAINT [IX_ZData] UNIQUE NONCLUSTERED 
(
	[Pid] ASC,
	[EntryID] ASC,
	[Date] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, 
SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, 
ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
GO

測試，發現速度快很多，減小了timeout的風險。