Question

请参阅以下用于写入文本文件的代码。但数据库提取了近1百万条记录，所以有人可以建议更快的方式来做到这一点，或者我应该如何更改下面提到的代码以使其更快地工作？

try
{
    using (OleDbConnection connection = new OleDbConnection(ConnectionString))
    {
        OleDbCommand command = new OleDbCommand(queryString, connection);
        connection.Open();
        OleDbDataReader reader = command.ExecuteReader();
        DataTable dt = new DataTable();
        dt.Load(reader);

        StreamWriter writer = new StreamWriter(FilePath + FileName);
        var result = string.Empty;
        for (int i = 0; i < dt.Rows.Count; i++)
        {
            for (int j = 0; j < dt.Columns.Count; j++)
            {
                result += dt.Rows[i][j] + "|";
            }
            result += "\r\n";
        }
        writer.WriteLine(result);

        reader.Close();
        writer.Close();

        Dts.TaskResult = (int)ScriptResults.Success;
    }
}

Answer 1

您在数据表中加载了100万条记录，然后在该表上再次循环以写入每一行。

也许你可以做同样的事情，但是如果你读了一行并把它写下来，有一半的时间是这样的：

OleDbDataReader reader = command.ExecuteReader();
StreamWriter writer = new StreamWriter(FilePath + FileName);
var result = string.Empty;
while(reader.Read())
{
    for (int j = 0; j < reader.FieldCount; j++)
    {
        result += reader[j] + "|";
    }
    result += "\r\n";
}
writer.WriteLine(result);

此外，在这种情况下，使用StringBuilder缓冲内存中的读取而不是经常写入磁盘可能非常有用：

// This size is just for example purpose. Should be fine tuned
StringBuilder buffer = new StringBuilder(1048576);
while(reader.Read())
{
    for (int j = 0; j < reader.FieldCount; j++)
    {
        buffer.Append(reader[j] + "|");
    }
    buffer.AppendLine();
    if(buffer.Length > 1048576 - 1024)
    {
        writer.Write(buffer.ToString());
        buffer.Length = 0;
    }
}
writer.Write(buffer.ToString());

将一百万行写入文本文件

1 个答案: