C＃桌面应用程序：SQL Server访问突然变慢

Question

我的C＃桌面应用程序具有ItemsBrowser形式。 我的应用程序是关于库存系统的。 当用户添加新销售或新购买商品时， ItemsBrowser表单将加载Items Details。 这是LoadAllItems()代码：-

    void LoadAllItems()
    {
        DBConnector dbc = new DBConnector();
        AccountsBasic.Classes.DBConnector dbca = new AccountsBasic.Classes.DBConnector();
        ArrayList lstItems = dbc.GetAllItems();
        var AddedItems = new List<DataGridViewRow>();

        Cursor.Current = Cursors.WaitCursor;
        dgvItems.Rows.Clear();
        for (int i=0; i<=lstItems.Count-1; i++)
        {
            Item itm = (Item)lstItems[i];
            ItemCategory ItemCat = dbc.GetThisItemCategory(itm.ItemCategoryCode);
            DataGridViewRow row = new DataGridViewRow();
            row.CreateCells(dgvItems);              
            row.Cells[0].Value = dbca.GetThisParty(dbc.GetThisItemCategory(itm.ItemCategoryCode).SupplierCode).PartyName;
            row.Cells[1].Value = ItemCat.ItemCategoryName;
            row.Cells[2].Value = itm.ItemID.ToString();
            row.Cells[3].Value = itm.ItemName;
            row.Cells[4].Value = itm.RetailPrice.ToString();
            row.Cells[5].Value = dbc.GetPresentStock_By_ItemID(itm.ItemID).ToString();

            AddedItems.Add(row);
            //dgvItems.Rows.Add(dbca.GetThisParty(dbc.GetThisItemCategory(itm.ItemCategoryCode).SupplierCode).PartyName, dbc.GetThisItemCategory(itm.ItemCategoryCode).ItemCategoryName, itm.ItemID.ToString(), itm.ItemName, itm.RetailPrice, dbc.GetPresentStock_By_ItemID(itm.ItemID).ToString());
        }

        dgvItems.Rows.AddRange(AddedItems.ToArray());
        dgvItems.AutoResizeColumns();
        Cursor.Current = Cursors.Default;
    }

此功能运行正常且速度很快。 但是突然它变得非常慢。 通过在循环中逐行检查每一行，我发现当一条语句访问诸如ItemCategory ItemCat = dbc.GetThisItemCategory(itm.ItemCategoryCode);的数据库时， ItemCategory ItemCat = dbc.GetThisItemCategory(itm.ItemCategoryCode); 数据库访问变得非常慢。 尽管之前运行得还不错。 表格中共有955项。

我还发现了一种非常奇怪的东西...

我已经将此应用程序安装在客户端计算机上，并且在客户端计算机上可以正常运行，没有延迟...

GetAllItems（）函数

public ArrayList GetAllItems(string SupplierCode = "", string ItemCategory = "")
{
    if (SupplierCode != "" && ItemCategory != "")
        comm.CommandText = "SELECT Items.ItemID, Items.ItemName, Items.Description, Items.ItemCategoryCode, Items.OpeningStock, Items.RetailPrice FROM Items, ItemCategories WHERE Items.ItemCategoryCode = ItemCategories.ItemCategoryCode AND ItemCategories.SupplierCode = '" + SupplierCode + "' AND ItemCategories.ItemCategory = '" + ItemCategory + "' ORDER BY Items.ItemID";
    else if (SupplierCode != "" && ItemCategory == "")
        comm.CommandText = "SELECT Items.ItemID, Items.ItemName, Items.Description, Items.ItemCategoryCode, Items.OpeningStock, Items.RetailPrice FROM Items, ItemCategories WHERE Items.ItemCategoryCode = ItemCategories.ItemCategoryCode AND ItemCategories.SupplierCode = '" + SupplierCode + "' ORDER BY ItemCategories.SupplierCode, ItemCategories.ItemCategory";
    else if (SupplierCode == "" && ItemCategory != "")
        comm.CommandText = "SELECT Items.ItemID, Items.ItemName, Items.Description, Items.ItemCategoryCode, Items.OpeningStock, Items.RetailPrice FROM Items, ItemCategories WHERE Items.ItemCategoryCode = ItemCategories.ItemCategoryCode AND ItemCategories.ItemCategory = '" + ItemCategory + "' ORDER BY Items.ItemID";
    else
        comm.CommandText = "SELECT * FROM Items Order By ItemID";

    ArrayList AllItems = new ArrayList();
    conn.Open();
    SqlDataReader dr;
    dr = comm.ExecuteReader();
    while (dr.Read())
    {
        Item it = new Item();
        it.ItemID = dr.GetInt32(0);
        it.ItemName = dr.GetString(1);
        it.Description = dr.IsDBNull(2) ? "" : dr.GetString(2);
        it.ItemCategoryCode = dr.IsDBNull(3) ? -1 : dr.GetInt32(3);
        it.OpeningStock = dr.IsDBNull(4) ? 0 : dr.GetInt32(4);
        it.RetailPrice = dr.IsDBNull(5) ? 0 : dr.GetDouble(5);

        AllItems.Add(it);
    }
    dr.Close();
    conn.Close();

    return AllItems;
}

GetThisItemCategory（）函数

    public ItemCategory GetThisItemCategory(int ItemCategoryCode = -1, string SupplierCode = "", string ItemCategory = "")
{
    if (ItemCategoryCode == -1 && SupplierCode != "" && ItemCategory != "")
        comm.CommandText = "SELECT * FROM ItemCategories WHERE SupplierCode = '" + SupplierCode + "' AND ItemCategory = '" + ItemCategory + "' Order By SupplierCode, ItemCategory";
    else if (ItemCategoryCode == -1 && SupplierCode == "" && ItemCategory != "")
        comm.CommandText = "SELECT * FROM ItemCategories WHERE ItemCategory = '" + ItemCategory + "' Order By ItemCategory";
    else// if (ItemCategoryCode != -1 && SupplierCode == "" && ItemCategory == "")
        comm.CommandText = "SELECT * FROM ItemCategories WHERE ItemCategoryCode = '" + ItemCategoryCode + "' Order By SupplierCode, ItemCategory";

    SqlDataReader dr;
    ItemCategory ic = new ItemCategory();
    ic.ItemCategoryCode = -1;

    conn.Open();
    dr = comm.ExecuteReader();
    if (dr.Read())
    {
        ic.ItemCategoryCode = dr.GetInt32(0);
        ic.SupplierCode = dr.GetString(1);
        ic.ItemCategoryName = dr.GetString(2);
        ic.OrderableStockLimit = (dr.IsDBNull(3)) ? -1 : dr.GetInt32(3);
    }
    dr.Close();
    conn.Close();

    return ic;
}

实际上，问题不在于特定功能。 它与任何数据库访问有关，无论是GetThisItemCategory（）还是GetPresentStock_By_ItemID（）函数。

请注意，早些时候它很漂亮。 突然，它开始表现出这种方式...

Answer 1

您需要学习如何执行“命名参数”，以防止注入的SQL攻击，并从RDBMS获得最大的计划重用。

这是一个例子：

using System;
using System.Data;
using System.Data.SqlClient;

class ParamDemo
{
    static void Main()
    {
        // conn and reader declared outside try
        // block for visibility in finally block
        SqlConnection conn   = null;
        SqlDataReader reader = null;

        string inputCity = "London";
        try
        {
            // instantiate and open connection
            conn =  new 
                SqlConnection("Server=(local);DataBase=Northwind;Integrated Security=SSPI");
            conn.Open();

            // don't ever do this
            // SqlCommand cmd = new SqlCommand(
            // "select * from Customers where city = '" + inputCity + "'";

            // 1. declare command object with parameter
            SqlCommand cmd = new SqlCommand(
                "select * from Customers where city = @City", conn);

            // 2. define parameters used in command object
            SqlParameter param  = new SqlParameter();
            param.ParameterName = "@City";
            param.Value         = inputCity;

            // 3. add new parameter to command object
            cmd.Parameters.Add(param);

            // get data stream
            reader = cmd.ExecuteReader();

            // write each record
            while(reader.Read())
            {
                Console.WriteLine("{0}, {1}", 
                    reader["CompanyName"], 
                    reader["ContactName"]);
            }
        }
        finally
        {
            // close reader
            if (reader != null)
            {
                reader.Close();
            }

            // close connection
            if (conn != null)
            {
                conn.Close();
            }
        }
    }
}

http://csharp-station.com/Tutorial/AdoDotNet/Lesson06

您可以在本文中阅读有关动态sql的一些信息。

http://sqlmag.com/database-performance-tuning/don-t-fear-dynamic-sql

（您的.cs C＃“内联” SQL与本文之间有一个很小的重叠...如果您愿意，它将为您提供一些进一步研究的内容）

.....

最后，您需要学习“索引调整”的基础知识。

您可以在这里进行介绍：

https://sqlserverperformance.wordpress.com/2010/04/06/a-dmv-a-day-%E2%80%93-day-7/

作为一个猜测，我会在

ItemCategories.ItemCategoryCode

和一个单独的索引

ItemCategories.SupplierCode

附加：

最后，您可以尝试使用此版本的代码吗？

您希望尽快摆脱DataReader，因此您的连接池不会耗尽连接。

public ItemCategory GetThisItemCategory(int ItemCategoryCode = -1, string SupplierCode = "", string ItemCategory = "")
{

    using (SqlCommand cmd = new SqlCommand("MyConnectionString")
    {

        /* TO DO !!! , build your sql-string and parameter list here */

        using (IDataReader dataReader = cmd.ExecuteReader(CommandBehavior.CloseConnection))
        {

            if /*while*/ (dataReader.Read())
            {
                ic.ItemCategoryCode = dr.GetInt32(0);
                ic.SupplierCode = dr.GetString(1);
                ic.ItemCategoryName = dr.GetString(2);
                ic.OrderableStockLimit = (dr.IsDBNull(3)) ? -1 : dr.GetInt32(3);
            }

            if (dataReader != null)
            {
                try
                {
                    dataReader.Close();
                }
                catch { }
            }           

        }

        cmd.Close();

    }

    return ic;

}