EF SqlQuery查询比直接查询慢20倍是否正常？

Question

I am trying to track down performance issues. I am running the following SQL query against a SQL Server Express database:

SELECT COUNT(OrderID)
  FROM FutureOrderHeader
 WHERE ScheduledFulfillmentTime >= {0}
   AND ScheduledFulfillmentTime <  {1}
   AND SplitStatus <> 2
   AND Deleted = 0
   AND OrderMode = {2}

When I run the command using Entity Framework as follows:

var results = ((DbContext)this._context).Database.SqlQuery<int>(SQL,start.BoxToSqlDataTime(),end.BoxToSqlDataTime(), (int)mode).Single();

It is approximately 20x slower then if I run the command through ADO.NET. Using SQL Server Profiler and EF Profiler, I was able to determine that the queries are the same. Executing this query through EF approx. 720 times takes an average of 2837ms. Running the same query using straight ADO.NET takes an average 146ms.

In SQL Server Profiler, the actual SQL text which is executed as well as the duration, cpu usage, reads, etc. are the same whether I am using EF or ADO.NET. According to SQL Server Profiler, the query itself takes between 0ms and 2ms regardless of whether I am using EF or straight ADO.NET.

I was wondering if this performance hit is normal or if I am missing something.

Thanks!

Answer 1

No, I would not say that is normal. While there are things that EF and Linq-to-SQL do poorly that do result in some horribly performing queries, getting a simple count with a where clause should perform just fine.

I would recommend profiling the EF call in call to see what is actually being executed. Looking at EF Code query you provided, it doesn't appear to be the same query. You can then alter the EF code or build appropriate indices to get the performance you are looking for.