Question

我有一个MySQL数据库“DB”，其中有一个表“TABLE”的单个字段，它包含大约8百万行。我试图将该表下载到文本文件中，如下所示：

//Open connection.
connection.Open();

//Create command.
MySqlCommand command = connection.CreateCommand();
command.CommandText = "SELECT * FROM `DB`.`TABLE`";

//Execute command.
MySqlDataReader result = command.ExecuteReader();

//If result isn't null
if (result != null)
{
    //Open stream to write result.
    System.IO.StreamWriter file = new System.IO.StreamWriter(@"C:\Users\StackOverflow\Desktop\ID_List.txt", true);

    //For each line row of result.
    while (result.Read())
    {
        //Write result in a line.
        file.WriteLine(result.GetValue(0).ToString());
    }
}

//Close connection.
connection.Close();

运行后，它开始下载数据并将其输出到文本文件，但只需一两分钟就可以得到：

An unhandled exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in test program.exe

Additional information: Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.

我可能会改变或做些什么来使它起作用？感谢您的任何建议和答案：）

[编辑]：我添加了command.CommandTimeout = 240;并测试了三次，每次下载几分钟（每次大约40MB的数据），然后给出：

An unhandled exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in test program.exe

Additional information: Fatal error encountered during data read.

这些是调试输出的最后几行：

at MySql.Data.MySqlClient.NativeDriver.FetchDataRow(Int32 statementId, Int32 columns) in :line 0
   at MySql.Data.MySqlClient.Driver.FetchDataRow(Int32 statementId, Int32 columns) in :line 0
   at MySql.Data.MySqlClient.ResultSet.GetNextRow() in :line 0
   at MySql.Data.MySqlClient.ResultSet.NextRow(CommandBehavior behavior) in :line 0
   at MySql.Data.MySqlClient.MySqlDataReader.Read() in :line 0</ExceptionString><InnerException><ExceptionType>System.IO.EndOfStreamException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</ExceptionType><Message>Attempted to read past the end of the stream.</Message><StackTrace>   at MySql.Data.MySqlClient.MySqlStream.ReadFully(Stream stream, Byte[] buffer, Int32 offset, Int32 count) in :line 0
   at MySql.Data.MySqlClient.MySqlStream.LoadPacket() in :line 0</StackTrace><ExceptionString>System.IO.EndOfStreamException: Attempted to read past the end of the stream.
   at MySql.Data.MySqlClient.MySqlStream.ReadFully(Stream stream, Byte[] buffer, Int32 offset, Int32 count) in :line 0
   at MySql.Data.MySqlClient.MySqlStream.LoadPacket() in :line 0</ExceptionString></InnerException></InnerException></Exception></TraceRecord>
An unhandled exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in test program.exe
Additional information: Fatal error encountered during data read.
The program '[4548] test program.exe: Program Trace' has exited with code 0 (0x0).
The program '[4548] test program.exe: Managed (v4.0.30319)' has exited with code 0 (0x0).

[EDIT2]：我添加MySqlDataReader result = command.ExecuteReader(System.Data.CommandBehavior.SingleResult);以弥补上述错误，现在我得到了：

An unhandled exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in test program.exe
Additional information: Query execution was interrupted

经过一些轻微的谷歌后，我认为是GoDaddy限制了查询执行时间。因此，一个可行的解决方案是使用try / catch来计算，以跟踪在连接关闭之前检索了多少记录，并重新打开与计数器的新连接作为LIMIT的起点直到表大小耗尽。 / p>

感谢您的帮助！

Answer 1

增加my.ini文件中的wait_timeout参数。

http://dev.mysql.com/doc/refman/5.0/en/server-system-variables.html#sysvar_wait_timeout

还有其他超时参数可能是问题，但我认为它就是那个。

如果您无权访问ini文件，请使用“限制”来获取有限的结果集。

首先，获取总行数（count（*））其次，感谢for

得到小的结果集

 for (int i=0; i<=numberOfRowsInYourTable ; i=i+1000){
      command.CommandText = "SELECT * FROM `DB`.`TABLE` LIMIT " + i + " " + new String(i + 1000);
      // Do what you want
 }

Answer 2

将此添加到您的连接字符串：

default command timeout=240

并根据需要进行调整。

Answer 3

你有几个选择

您可以设置更长的超时时间这意味着您需要在连接字符串

CommandTimeout parameter

您可以使用会在服务器上生成文件的SELECT INTO
您可以使用也会在服务器上生成文件的mysqldump实用程序

修改 SO用户提到了其他类型的超时参数。我不是用户哪一个是关键

将大型数据表从MySQL数据库下载到C＃中的文本文件

3 个答案: