【发布时间】：2012-11-18 23:34:27
【问题描述】：
所以我们在工作中就采取哪种 DataAccess 路由进行了激烈的辩论：DataTable 还是 DataReader。
免责声明我在 DataReader 方面，这些结果震撼了我的世界。
我们最终编写了一些基准来测试速度差异。人们普遍认为 DataReader 更快，但我们想看看能快多少。
结果让我们感到惊讶。 DataTable 始终比 DataReader 快。有时接近两倍。
所以我转向你们，SO 的成员。为什么，当大多数文档甚至 Microsoft 都声明 DataReader 更快时，我们的测试却显示相反。
现在是代码：
测试工具：
private void button1_Click(object sender, EventArgs e)
{
System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
sw.Start();
DateTime date = DateTime.Parse("01/01/1900");
for (int i = 1; i < 1000; i++)
{
using (DataTable aDataTable = ArtifactBusinessModel.BusinessLogic.ArtifactBL.RetrieveDTModified(date))
{
}
}
sw.Stop();
long dataTableTotalSeconds = sw.ElapsedMilliseconds;
sw.Restart();
for (int i = 1; i < 1000; i++)
{
List<ArtifactBusinessModel.Entities.ArtifactString> aList = ArtifactBusinessModel.BusinessLogic.ArtifactBL.RetrieveModified(date);
}
sw.Stop();
long listTotalSeconds = sw.ElapsedMilliseconds;
MessageBox.Show(String.Format("list:{0}, table:{1}", listTotalSeconds, dataTableTotalSeconds));
}
这是 DataReader 的 DAL：
internal static List<ArtifactString> RetrieveByModifiedDate(DateTime modifiedLast)
{
List<ArtifactString> artifactList = new List<ArtifactString>();
try
{
using (SqlConnection conn = SecuredResource.GetSqlConnection("Artifacts"))
{
using (SqlCommand command = new SqlCommand("[cache].[Artifacts_SEL_ByModifiedDate]", conn))
{
command.CommandType = CommandType.StoredProcedure;
command.Parameters.Add(new SqlParameter("@LastModifiedDate", modifiedLast));
using (SqlDataReader reader = command.ExecuteReader())
{
int formNumberOrdinal = reader.GetOrdinal("FormNumber");
int formOwnerOrdinal = reader.GetOrdinal("FormOwner");
int descriptionOrdinal = reader.GetOrdinal("Description");
int descriptionLongOrdinal = reader.GetOrdinal("DescriptionLong");
int thumbnailURLOrdinal = reader.GetOrdinal("ThumbnailURL");
int onlineSampleURLOrdinal = reader.GetOrdinal("OnlineSampleURL");
int lastModifiedMetaDataOrdinal = reader.GetOrdinal("LastModifiedMetaData");
int lastModifiedArtifactFileOrdinal = reader.GetOrdinal("LastModifiedArtifactFile");
int lastModifiedThumbnailOrdinal = reader.GetOrdinal("LastModifiedThumbnail");
int effectiveDateOrdinal = reader.GetOrdinal("EffectiveDate");
int viewabilityOrdinal = reader.GetOrdinal("Viewability");
int formTypeOrdinal = reader.GetOrdinal("FormType");
int inventoryTypeOrdinal = reader.GetOrdinal("InventoryType");
int createDateOrdinal = reader.GetOrdinal("CreateDate");
while (reader.Read())
{
ArtifactString artifact = new ArtifactString();
ArtifactDAL.Map(formNumberOrdinal, formOwnerOrdinal, descriptionOrdinal, descriptionLongOrdinal, formTypeOrdinal, inventoryTypeOrdinal, createDateOrdinal, thumbnailURLOrdinal, onlineSampleURLOrdinal, lastModifiedMetaDataOrdinal, lastModifiedArtifactFileOrdinal, lastModifiedThumbnailOrdinal, effectiveDateOrdinal, viewabilityOrdinal, reader, artifact);
artifactList.Add(artifact);
}
}
}
}
}
catch (ApplicationException)
{
throw;
}
catch (Exception e)
{
string errMsg = String.Format("Error in ArtifactDAL.RetrieveByModifiedDate. Date: {0}", modifiedLast);
Logging.Log(Severity.Error, errMsg, e);
throw new ApplicationException(errMsg, e);
}
return artifactList;
}
internal static void Map(int? formNumberOrdinal, int? formOwnerOrdinal, int? descriptionOrdinal, int? descriptionLongOrdinal, int? formTypeOrdinal, int? inventoryTypeOrdinal, int? createDateOrdinal,
int? thumbnailURLOrdinal, int? onlineSampleURLOrdinal, int? lastModifiedMetaDataOrdinal, int? lastModifiedArtifactFileOrdinal, int? lastModifiedThumbnailOrdinal,
int? effectiveDateOrdinal, int? viewabilityOrdinal, IDataReader dr, ArtifactString entity)
{
entity.FormNumber = dr[formNumberOrdinal.Value].ToString();
entity.FormOwner = dr[formOwnerOrdinal.Value].ToString();
entity.Description = dr[descriptionOrdinal.Value].ToString();
entity.DescriptionLong = dr[descriptionLongOrdinal.Value].ToString();
entity.FormType = dr[formTypeOrdinal.Value].ToString();
entity.InventoryType = dr[inventoryTypeOrdinal.Value].ToString();
entity.CreateDate = DateTime.Parse(dr[createDateOrdinal.Value].ToString());
entity.ThumbnailURL = dr[thumbnailURLOrdinal.Value].ToString();
entity.OnlineSampleURL = dr[onlineSampleURLOrdinal.Value].ToString();
entity.LastModifiedMetaData = dr[lastModifiedMetaDataOrdinal.Value].ToString();
entity.LastModifiedArtifactFile = dr[lastModifiedArtifactFileOrdinal.Value].ToString();
entity.LastModifiedThumbnail = dr[lastModifiedThumbnailOrdinal.Value].ToString();
entity.EffectiveDate = dr[effectiveDateOrdinal.Value].ToString();
entity.Viewability = dr[viewabilityOrdinal.Value].ToString();
}
这是 DataTable 的 DAL：
internal static DataTable RetrieveDTByModifiedDate(DateTime modifiedLast)
{
DataTable dt= new DataTable("Artifacts");
try
{
using (SqlConnection conn = SecuredResource.GetSqlConnection("Artifacts"))
{
using (SqlCommand command = new SqlCommand("[cache].[Artifacts_SEL_ByModifiedDate]", conn))
{
command.CommandType = CommandType.StoredProcedure;
command.Parameters.Add(new SqlParameter("@LastModifiedDate", modifiedLast));
using (SqlDataAdapter da = new SqlDataAdapter(command))
{
da.Fill(dt);
}
}
}
}
catch (ApplicationException)
{
throw;
}
catch (Exception e)
{
string errMsg = String.Format("Error in ArtifactDAL.RetrieveByModifiedDate. Date: {0}", modifiedLast);
Logging.Log(Severity.Error, errMsg, e);
throw new ApplicationException(errMsg, e);
}
return dt;
}
结果：
测试工具中的 10 次迭代
测试工具中的 1000 次迭代
这些结果是第二次运行，以减轻由于创建连接而产生的差异。
【问题讨论】：
-
最终结果不同。一个给你一个DataTable，一个给你一个List
。据我所知，DataTable 存储了所有未解析的内容，并且会在您阅读时对其进行解析（我实际上不知道 DataTables 如何在内部存储它们的数据，我一直怀疑它是 XML-ish）我知道 DataTables 会浪费读者的内存。 -
您是在调试器内部还是外部运行比较？调试器通常会减慢您自己的代码的速度，而对于已经编译的框架代码，即使在发布模式下也是如此。
-
令我感到非常惊讶的另一件事是没人提到 DataTable 使用 GetValues(object[]) 一次加载一整行，而您的代码分别加载每个字段。实际上，每个单独的调用都会产生一些开销，并且开销可能足够大以使 DataTable 加载更快。
标签： .net data-access-layer sqldatareader