与SQL相比，EF Linq QUery原因锁定

Question

I have a simple count query using LINQ and EF:

var count = (from I in db.mytable
             where xyz
             select I).Count();

the code above shows the query being locked in the database.

while the execute sql executes right away:

var count = db.SqlQuery<int>("select count(*) from mytable where xyz").FirstOrDefault();

the code above returns immediately.

I few have suggested to remove the .ToList() which I did and not difference. One thing is that this only happens on the PROD server. The QA server executes pretty fast as expected. But the prod server shows that it gets suspended. I suspect this could be a data storage limitation or server related. But wanted to make sure I am not doing something stupid in the code.

UPDATE:

One thing I noticed is the first time it execute is takes longer the first time. When I set next statement to run it again, it executes immediately. Is there a compile of the query the first time?

Answer 1

Because you are calling ToList in the first query and that causes fetching all records from DB and do the counting in memory. Instead of ToList you can just call Count() to get the same behaviour:

var count = (from I in db.mytable
              where xyz
              select I).Count();

Answer 2

You must not call .ToList() method, because you start retrieve all objects from database. Just call .Count()

var count = (from I in db.mytable
             where xyz
             select I).Count(); 

Answer 3

Count can take a predicate. I'm not sure if it will speed up your code any but you can write the count as such.

var count = db.mytable.Count(x => predicate);

Where predicate is whatever you are testing for in your where clause.

Simple fiddling in LINQPad shows that this will generate similar, if not exactly the same, SQL as above. This is about the simplest way, in terseness of code, that I know how to do it.

If you need much higher speeds than what EF provides, yet stay in the confines of EF without using inline SQL you could make a stored procedure and call it from EF.