I noticed that if I specify a constant in an EF query that the value gets inlined, but if I specify that same value as a variable then EF creates a subquery for it and passes it in as a parameter. Are there any performance differences between the two approaches?
I have some massive Linq queries and I'm wondering if using constants might help with performance in terms of both the query execution (and plan caching) and in the translation from Linq to SQL.
I suggest you check out this article from TechNet:
https://technet.microsoft.com/en-us/library/ms175580(v=sql.105).aspx
It states that if you use literals, then the query optimizer should recognize it, but sometimes it might not.
The only difference between the execution plans for these queries is
the value stored for the comparison against the ProductSubcategoryID
column. While the goal is for SQL Server to always recognize that the
statements generate essentially the same plan and reuse the plans, SQL
Server sometimes does not detect this in complex SQL statements.
Note the words "complex" and "sometimes" — quite a concrete explanation, isn't it? :)
The article also goes on to explain that if you use parameters, it "helps" the engine to reuse plans (again, concrete), some things about simple parameterization and forced parameterization.
So the documentation says that it is not certain, but usually this should not make a difference. As or my own experience: I've found that the engine is able to recognize the constants in queries generated by EF quite well. I had the same question a while back, and did some checking on Azure SQL. I wouldn't say I examined the most complex generated SQL queries of the world, but they were not just simple select-where-let-join combos.
But again, that was for my queries in a specific version of the engine. To be sure, I would suggest you also check your queries in question, and then you can be sure.
I have two opinion about manipulating data with c# programming language environment.
(select * from where ...) query with sql and get data.
(select * from) get all data and use Linq query on object list.
What is the performance difference about these opinions for big size or avarage size data. Can I use both of them?
The generic answer to performance is questions is to try it on your data and see which works better.
In your case, though, there is a right answer: Do the work in the database.
Filtering the data in the database (using the where) has two advantages. First, it reduces the amount of data sent from the database to the application. This is almost always a win (unless almost all rows are returned).
Second, it allows the database to optimize the query, using (for instance) available indexes to speed the query.
Personally - if you can reduce the amount of data you suck into memory from the database, do it. Why download 10M records, when you needed 100k.. then refine it more with linq for simplicity maybe using local conditions etc. For small data you can probably try both - although depending on what your linq is connected to object wise you could still be performing sql anyway, so...
I assume you're talking about LinqToSql here and the resulting queries are equivalent. If that is the case the only difference in terms of performance is LinqToSql overhead of translating c# expression tree to SQL query. And it's pretty serious as the process involves DB provider which uses reflection and complex logic of converting the tree.
I've just started reading about LINQ and there is one thing that's been bugging me. LINQ turns a LINQ query into a corresponding SQL query to a database server. Since I doubt that LINQ can convert any code to an SQL statement I must assume that there are some limits here.
Since I want to have the query that is sent to the server as restrictive as possible, what can LINQ turn into SQL and what can't LINQ turn into SQL?
For example where employee.name == "Test" looks pretty trivial to convert, but what about where isEven(employee.number)? Or something more complex?
Here is the MSDN page detailing which methods LINQ to SQL supports.
You will not be able to use your own method calls inside of the expression tree, as LINQ to SQL does not understand how to convert the methods into SQL.
Some ORMs (e.g. NHibernate) allow you to define your own generators for generating SQL (HQL in NHibernates case) for your own methods, I do not believe L2S supports this.
I have read many articles about linq to sql performance. The result which i got is it is slower than normal approach(DAL or Microsoft Enterprise library). Slower for both read and write operations even after performance tuning like disable ObjectTracking and other tricks. I know it has prons like quick development, clean code etc but what about the performance.
What if i used only for read operations.
Please give your suggestions.
It seems to work well enough for stackoverflow ;-p Especially if you use compiled queries, this is unlikely to be your bottleneck, compared (for example) to appropriate DB design and fetching the right columns / rows, and avoiding n+1 loading.
For read operations LINQ To SQL should be roughly as fast as directly writing the SQL because that's exactly what it does. The overhead of creating the SQL shouldn't be noticable. There might be a few queries that it doesn't get as optimal as if you wrote the query by hand, but in my experience it does very well in most cases.
For bulk updates, LINQ To SQL is typically slower because it handles rows one at a time. You can't do something like UPDATE Foo SET x = 0 WHERE id BETWEEN 100 AND 200 in LINQ to SQL without fetching all the rows. It's currently best to write the SQL by hand for this type of operation.
The updates and deletes is where LINQ to SQL currently suffers since a separate statement is generated for each affected object.
That said, this blog post details how to get both operations down to 1 statement, which should help improve performance: Batch Updates and Deletes with LINQ to SQL.
Compiled queries will also come in handy for frequently used queries, especially those where parameters are used to get specific results. You might also find this post helpful: 10 Tips to Improve your LINQ to SQL Application Performance.
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Are there any good Reasons not to use LINQ in my projcts? We use .Net 3.5 and VSTO 3.0.
Personally I can't see why you wouldn't want to use it, it makes code much more readable.
With that being said, LINQ can sometimes be detrimental to performance in certain scenarios, that would really only be my reason for not using it.
The other answers have implied this, but here it is explicitly:
The term "LINQ" can refer to the overall set of technologies for Language INtegrated Query. These technologies permit a LINQ Query to be turned into an expression tree. That tree can be executed at a later time, by a "LINQ Provider".
The LINQ Provider looks at the expression tree and converts it into, for instance, SQL statements, or XML DOM navigation, or navigation through an object graph. These providers have names like "LINQ to SQL", "LINQ to Entities", "LINQ to Objects", etc.
There could be reasons to not use a specific provider.
Many of the individual LINQ providers come with additional tooling (some would say, "baggage"). This tooling helps provide some of the most common "pros and cons" about LINQ.
In particular, LINQ to SQL provides a direct, one to one mapping to the database schema. Each LINQ class corresponds to a single database table. If the structure of the database changes, then so does the code. This can be mitigated to an extent by using views.
I believe that LINQ to SQL is limited to Microsoft SQL Server. Also, Microsoft has stated that LINQ to SQL will not be a priority investment going forward.
LINQ to Entities is part of the ADO.NET Entity Framework (EF). EF provides for modeling your entities in a more abstract, conceptual level. For instance, you might have a Person entity that takes data from two tables that have a one to one mapping. Code accessing this entity need not care how the tables are broken out in the database.
I believe that LINQ to Entities is meant to work with many ADO.NET providers, not just SQL Server. Also, this is where Microsoft says it will be placing its investments going forward.
In both of these cases of LINQ to "some database", it's almost always going to be the case that a experienced SQL developer and/or DBA can write better queries than will be generated by LINQ. If performance is the top requirement, I believe that LINQ to Entities can map stored procedures into methods on the entities.
The big benefit of these LINQ providers is that you don't need that experienced SQL developer or DBA when you're working in an environment where performance is not the top priority. This frees them up to optimize queries that actually require their expertise.
Another reason not to use these directly is if you have security considerations preventing your users from having SELECT permissions to the database tables. In that case, use views or stored procedures.
Yes, there are reasons. I'm going to talk about some of the difficulties I've faced when using various LINQ providers for RDBMS.
LINQ works great in most cases, but when you want to build complex queries (e.g. in reporting apps) it's statically-typed nature becomes a disadvantage. It's hard to, for instance, conditionally JOIN, or conditionally GROUP BY, because the result type changes, even if in the end you want to project the same fields. It's also hard to do LEFT JOIN. If you really appreciate dynamic queries then SQL and ESQL are better options.
Also, the same LINQ query can be (and usually is) interpreted differently depending on the provider, which can lead to unexpected results when switching providers.
About SQL functions, not all the functions you need are mapped to CLR methods, and not all providers offer a extensibility mechanism for mapping functions.
Finally, the performance issue. Converting expression trees to store queries can be expensive, and sometimes the end result is not the best possible query. The most elegant source code is not always the best runtime code.
The only reason would be if you have a very performance critical app as LINQ to Objects queries usually perform worse than for loops. This will change with .Net 4.0, when you can make use of PLINQ's parallel processing features.
Anyhow, if you have such a performance critical app, you probably should not use a managed environment anyways. in 99% of all cases LINQ will make your code more readable and more elegant. It's deferred execution mechanism may even gain you some performance under the right circumstances.
Well, if you want to make a step backwards and work 2xtimes longer on your projects you shouldn't use it ;-)
I think there is no real good reason to NOT use it. You are faster, smarter and you can make less mistakes and have more control since you can work "datatyped"
In a very short answer: no, there is no reason not to use Linq. Although it can be slightly hard to grasp for people new to the concept of functional programming (but only slightly), once you get the hang of it, you will love it, and it can in general greatly improve the readability of the code.
It depends on whether you're referring to LINQ to SQL or LINQ as a modelling tool. Personally I use LINQ for modelling only because my superiors who are actually less educated than me in this area refuse to it for a number of reasons. One reason is that they've stopped adding new features completely and are only maintaining bug fixes in LINQ now. Secondly is that it's supposedly slower than direct SQL, which to a certain degree is true when running lower end hardware perhaps, I don't know. Thirdly is a domain perspective, if you want to shy away from SQL injection vulnerabilities supposedly it's wise to use stored procedures instead. In all instances for us, we use LINQ for modelling only now, stored procedures are "compiled" on the server after being run for the first time.
Personally I just meet requirements, I have no powers for decision, but LINQ is great for modelling and includes many handy features.
The LINQ architecture is good - but some may prefer to read source code that does not use the LINQ SQL-like syntax. So if you're strict on readability, you may want not to use that syntax.
I have encountered some issues with it that I've had to work around. For example, depending on how your database relations are setup you may find that linq2sql works great for querying, but has trouble updating correctly. This happened to me and what I did was setup two sets of linq objects. The first had all the relationships I needed so I could use simpler syntax for querying, but the second didn't contain the relationships for when I wanted to update since I didn't need them then.
Performance shouldn't be a reason not to use it because generally that's only an issue for certain processes. And it's not like you have to use linq exclusively or not at all. I think a lot of people think "oh, direct sql is faster and there are some things I need to do that HAVE to be fast so I can't use linq". That's just silly though. Use it where you can, and use direct sql where you can't.
What I can figure out from various posts is that it depends on requirement
LINQ works independent of datasource ....work on file objects and database in same way
LINQ can reduce multiple queries into one
LINQ has the type safety
Overall good to use and faster development
LINQ still has a lot of open issues
LINQ has stopped evolving (nothing new coming up)
SQL is more reliable and more efficent
SQL is better when working with more complex queries, stored procedures
SQL is faster then LINQ-SQL
So depending on if your project requires inline queries not so complex and involves to query data sources other then relational database like SQL use LINQ otherwise go for good old SQL server.....:)
not to use LINQ if you mean LINQ as "LINQ to SQL" and your SQL Server has performance problem with a Adhoc Query Execution.
As for me - only one reason not to use LINQ. It is third-party enhancement tools for this product. I prefer - Devart LinqConnect, for example.
LINQ is a great technology, but produce a uggly code. If you thinking, you are a Picasso of code don't use it.
Produce code without LINQ is producing readable code. But i use always ;)
Yes, definitely makes things more readable and concise. Certainly did for the 15 years I used it in Visual FoxPro ;)