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

问题：

最近程序总会抛出如下异常：

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)......

读取数据超时。

然后就去看了下DataBase里对应的tables，发现table的结构简单，但是数据量很大，有几十万上百万条。再看一下有没有建Indexes/Keys，发现没有，恍然大悟。

解决方法：

根据表的结构，建立了Indexes/Keys下的 Unique key，类似如下：

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

测试，发现速度快很多，减小了timeout的风险。