每次编译后第一次加载实体框架非常慢 [英] Entity framework very slow to load for first time after every compilation

问题描述

As the title suggest i'm having a problem with the first query against a SQL Server database using the Entity Framework. I have tried looking for an answer but no one seems to actually have a solution to this.

The tests was done in Visual Studio 2012 using Entity Framework 6, I also used the T4 views template to pre-compile the views. The database was on a SQL Server 2008. We have about 400 POCOs (400 mapping files), only have 100 rows data in database table.

Following capture is my test code and result.

static void Main(string[] args){
    Stopwatch st=new Stopwatch();
    st.Start();
    new TestDbContext().Set<Table1>.FirstOrDefault();
    st.stop();
    Console.WriteLine("First Time "+st.ElapsedMilliseconds+ " milliseconds");

    st.Reset();
    st.Start();
    new TestDbContext().Set<Table1>.FirstOrDefault();
    st.stop();
    Console.WriteLine("Second Time "+st.ElapsedMilliseconds+ " milliseconds");
}

Test results

First Time 15480 milliseconds
Second Time 10 milliseconds

解决方案

On the first query EF compiles the model. This can take some serious time for a model this large.

Here are 3 suggestions: http://www.fusonic.net/en/blog/2014/07/09/three-steps-for-fast-entityframework-6.1-first-query-performance/

A summary:

1. Using a cached db model store
2. Generate pre-compiled views
3. Generate pre-compiled version of entityframework using n-gen to avoid jitting

I would also make sure that I compile the application in release mode when doing the benchmarks.

Another solution is to look at splitting the DBContext. 400 entities is a lot and it should be nicer to work with smaller chunks. I haven't tried it but I assume it would be possible to build the models one by one meaning no single load takes 15s. See this post by Julie Lerman https://msdn.microsoft.com/en-us/magazine/jj883952.aspx

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