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。
Timeout expired. The timeout period elapsed prior to completion of the operation or the server...
原文：http://blog.csdn.net/bubu05690523/article/details/44752743