Entity Framework Slow, News At 11

Jovan Popovic shows that Entity Framework is slow and Dapper is fast:

To setup test, you can go to StackExchange/Dapper GitHub an download source code. Tests are created as C# solution (Dapper.sln). When you open this solution you can find Dapper.Tests project. You might need to change two things:

  1. Connection strings are hardcoded in Tests.cs file with values like “Server=(local)\SQL2014;Database=tempdb;User ID=sa;Password=Password12!”. You might need to change this and put your connection info.
  2. Project is compiled using dotnet sdk 1.0.0-preview2-003121, so you might get compilation errors if you don’t have a matching framework. I have removed line: “sdk”: { “version”: “1.0.0-preview2-003121” } from global.json to fix this.

Now you will be able to build project and run tests.

Nothing’s going to be faster than hand-crafted, well-tuned statements from people who know what they’re doing.  Micro-ORMs like Dapper and FSharp.Data.SqlClient will trade a little bit of a speed hit for developer niceties.  Heavier frameworks like Entity Framework and NHibernate add a lot more, but tend to be significantly slower.

Data Type Mismatches

Kendra Little gets into why certain data type mismatches force scans of tables while others can still allow seeks:

Sometimes we get lucky comparing a literal value to a column of a different type.

But this is very complicated, and joining on two columns of different types in the same family without explicitly converting the type of one of the columns resulted in worse performance in Paul White’s tests, when the columns allowed NULLs! (Note: I haven’t rerun those tests on 2016, but I think the general advice below still applies.)

General advice: don’t rely on being lucky. Pay attention to your data types, and compare values of the same data type wherever possible.

That’s great advice.

Dr. Elephant: Where Does My Hadoop Cluster Hurt?

Carl Steinbach looks back at Dr. Elephant one year later:

What we needed to introduce to the job-tuning equation was a series of questions like those asked by a physician making a diagnosis: a step-by-step process that guides the user through the problem-solving process, while also educating them at the same time.

So we created Dr. Elephant, a system that automatically detects under-performing jobs, diagnoses the root cause, and guides the owner of the job through the treatment process. Dr. Elephant makes it easy to identify jobs that are wasting resources, as well as jobs that can achieve better performance without sacrificing efficiency. Perhaps most importantly, Dr. Elephant makes it easy to act on these insights by making job-level performance tuning accessible to users regardless of their previous skill level. In the process, Dr. Elephant has helped to ease the tension that previously existed between user productivity on one side and cluster efficiency on the other.

LinkedIn has made this project open source if you want to check it out in your environment.

Unnecessary, Mandatory Work

Lukas Eder lays out one of the biggest performance drains today:

We’re using 8x as much memory in the database when doing SELECT * rather than SELECT film, rating. That’s not really surprising though, is it? We knew that. Yet we accepted it in many many of our queries where we simply didn’t need all that data. We generated needless, mandatory work for the database, and it does sum up. We’re using 8x too much memory (the number will differ, of course).

Now, all the other steps (disk I/O, wire transfer, client memory consumption) are also affected in the same way, but I’m skipping those.

This article is absolutely worth reading and sharing with developers.

Batch Requests Per Second

Tara Kizer explains the Batch Requests/sec metric:

WHAT IS BATCH REQUESTS/SEC?

Batch Requests/sec is a performance counter that tells us the number of T-SQL command batches received by the server per second. It is in the SQLServer:SQL Statistics performance object for a default instance or MSSQL$InstanceName:SQL Statistics for a named instance.

WHAT COMPRISES A BATCH?

If I execute a stored procedure that has multiple queries and calls to other stored procedures, what will Batch Requests/sec show? Let’s test it to find out.

Click through for the answer.

Lightweight Statistics Profiling

Arun Sirpal looks at trace flag 7412 in SQL Server 2016 SP1:

According to documentation online (https://msdn.microsoft.com/en-us/library/mt791503.aspx) it states that the new query execution statistics profiling infrastructure dramatically reduces performance overhead of collecting per-operator query execution statistics.

Read on, as Arun might have discovered a bug in it.

Performance Tuning A Streaming Application

Mathieu Dumoulin explains how he was able to get 10x performance out of a streaming application built around Kafka, Spark Streaming, and Apache Ignite:

The main issues for these applications were caused by trying to run a development system’s code, tested on AWS instances on a physical, on-premise cluster running on real data. The original developer was never given access to the production cluster or the real data.

Apache Ignite was a huge source of problems, principally because it is such a new project that nobody had any real experience with it and also because it is not a very mature project yet.

I found this article fascinating, particularly because the answer was a lot more than just “throw some more hardware at the problem.”

The Cost Of Compression

Erin Stellato looks at the COMPRESS function:

While this data is interesting, I’m more curious about how compression affects my everyday SELECT queries. I have a set of three stored procedures that each have one SELECT query, so that each index is used. I created these procedures for each table, and then wrote a script to pull values for first and last names to use for testing. Here is the script to create the procedures.

Once we have the stored procedures created, we can run the script below to call them. Kick this off and then wait a couple minutes…

To me, the COMPRESS function is most useful for compressing information you tend not to search through but need to keep the in the database, like HTML markup or long descriptions.

Filtered Indexes And Parameters

Erik Darling shows an example of what happens when you have a filtered index and parameterize the filter:

It Is Known

That when you use filtered indexes, they get ignored when your queries are parameterized. This is a Plan Caching Thing©, of course. The simplest example is a bit column with a filtered index. If your index is on WHERE Bit = 1, it doesn’t have data for WHERE Bit = 0. That index would only be suitable for one variation of the query, so caching a plan that uses an index which can’t be reused for every variation isn’t feasible.

Read on for a couple examples, and check the comments on this as well.

BatchMode Execution

Sunil Agarwal describes BatchMode execution with columnstore indexes:

You may be wondering what is this magic number 900 rows within a batch? Well, when executing a query in BatchMode, SQL Server allocates a 64k bytes structure to group the rows. The number of rows in this structure can vary between 64 to 900 depending upon number of columns selected. For the example above, there are two columns that are referenced and X marks the rows that qualified in the BatchMode structure shown in the picture below. If SCAN is part of a bigger query execution tree,  the pointer to this structure is passed to the next operator for further processing. Not all operators can be executed in BatchMode. Please refer to Industry leading analtyics query performance for details on BatchMode Operators.

Under the right circumstances, BatchMode execution can be a major performance benefit.

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