17
因此，我們在工作中爭論着要採用哪種DataAccess路線：DataTable或DataReader。DataTable爲什麼比DataReader更快
免責聲明我在DataReader方面，這些結果動搖了我的世界。
我們寫了一些基準來測試速度差異。人們普遍認爲DataReader速度更快，但我們希望看到更快。
結果令我們驚訝。 DataTable始終比DataReader快。有時接近兩倍。
所以我轉向你，SO的成員。爲什麼當大多數文檔甚至是微軟聲明DataReader速度更快時，我們的測試顯示其他情況。
現在的代碼：
測試工具：
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));
}
這是DataReader的的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();
}
這是DAL的DataTable：
個 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;
}
結果：
對於10內的測試工具
迭代對於1000次迭代測試工具
這些結果內的是第二次運行，以減輕差異d用來創建連接。
最終結果不同。一個給你一個DataTable，一個給你一個List。對於我所知道的DataTable存儲所有未解析的內容，並在讀取時解析它（我實際上不知道DataTables如何在內部存儲它們的數據，我總是懷疑它是XML-ish）。我知道DataTables會浪費內存，而讀者卻不會。 –
MatthewMartin
您是在調試器內部還是外部運行比較？調試器通常會以非編譯框架代碼的速度放慢自己的代碼，即使在發佈模式下也是如此。 –
另一件我真的很驚訝的人沒有提到的是，DataTable一次加載一整行，使用GetValues（object []），而你的代碼分別加載每個字段。實際上，每次調用都會產生一些開銷，並且可能開銷足以使DataTable加載速度更快。 –