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Author: Kevin Feasel

Microsoft Research Open Data Sets

Published 2018-07-13 by Kevin Feasel

David Smith notes that there are several data sets that Microsoft Research has made available:

Other data sets of note include:

  • A collection of 38M tweets related to the 2012 US election

  • 3-D capture data from individuals performing a variety of hand gestures

  • Infer.NET, a framework for running Bayesian inference in graphical models

  • Images for 1 million celebrities, and associated tags

  • MS MARCO, is a new large-scale dataset for reading comprehension and question answering

Click through for more information, and then check out the data sets.

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Comparing System Metadata Between SQL Server Versions

Published 2018-07-13 by Kevin Feasel

Aaron Bertrand shows how he finds hidden features in new SQL Server builds:

One of the areas I like to focus on is new features in SQL Server. Under both MVP and Microsoft Partner programs, I get to see a lot of builds of SQL Server that don’t make it to the public, and documentation for these builds is typically sparse. In order to get a head start on testing things out, I often need to explore on my own. And so I wrote some scripts for that, which I’ve talked about in previous blog posts:

When I install a new version of SQL Server (be it a cumulative update, the final service pack for a major version, or the first CTP of vNext), there are two steps:

  1. Create a linked server to the build that came before it

  2. Create local synonyms referencing the important catalog views in the linked server

It’s a good way to get a glimpse at which features devs are currently working on but haven’t enabled yet.

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Why .NET And Java Have StringBuilders

Published 2018-07-13 by Kevin Feasel

Randolph West walks us through a performance troubleshooting issue with a twist:

So we branch the the code in source control, and start writing a helper class to manage the data for us closer to the application. We throw in a SqlDataAdapter, use the Fill() method to bring back all the rows from the query in one go, and then use a caching layer to keep it in memory in case we need it again. SQL Server’s part in this story has now faded into the background. This narrow table consumes a tiny 8 MB of RAM, and having two or more copies in memory isn’t the end of the world for our testing. So far, so good again.

We run the new code, first stepping through to make sure that it still does what it used to, massaging here and there so that in the end, a grid is populated on the application with the results of the query. Success! We then compile it in Release mode, and run it without any breakpoints to do some performance testing.

And then we find that it runs at exactly the same speed to produce exactly the same report, using our caching and SqlDataAdapter, and we’ve wasted another hour of our time waiting for the grid and report. Where did we go wrong?

As people get better at tuning, we start to make assumptions based on prior experience.  That, on net, is a good thing, but as Randolph shows, those assumptions can still be wrong.

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The Problems With NOLOCK

Published 2018-07-13 by Kevin Feasel

Rob Farley demonstrates the downside of the READ UNCOMMITTED isolation level:

I’m going to create a table and insert exactly 1 million rows. This particular table will be a clustered index, and will contain 1 million GUIDs.

Next I prove that there a million rows.

Now without inserting or deleting any rows, I’m going to shuffle them.

And if while this is happening, I count the rows in a different session, I have to wait for that query to finish.

Read on to see what happens when someone gets the idea of running the select query with NOLOCK.

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Get-DbaDbCompression DBATools Cmdlet

Published 2018-07-13 by Kevin Feasel

Jess Pomfret walks us through her recent contribution to dbatools:

I’ve been using this at work recently and it also relates to the presentation I gave at the ONSSUG June meeting around data compression. The beginnings of this script originated online as I dug into learning about the DMVs that related to objects and compression and then customized for what I needed.

If you run the below as is it will provide basic information about all objects in your database, except those in the ‘sys’ schema, along with their current size and compression level.

Click through for the script or, if your version of dbatools is up to date, call Get-DbaDbCompression.

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Building A Calendar Table

Published 2018-07-13 by Kevin Feasel

Louis Davidson has an example of a calendar table in SQL Server:

The solution is part of my calendar/date dimension code, and it is used to do relative positioning over date periods. For example, say you have the need to get data from the 10 days. You can definitely use a simple between to filter the rows, and a bunch of date functions to group by year, month, etc., generally all of the “normal” groupings. But using a calendar table allows you to prebuild a set of date calculations that make the standard values easier to get, and non-standard groupings possible. The technique I will cover makes moving around in the groupings more easily accessible. Like if you want data from the last 3 complete months. The query to do this isn’t rocket science, but it isn’t exactly straightforward either.

For the example, I will use the calendar table that I have on my website here: http://drsql.org/code in the download SimpleDateDimensionCreateAndLoad, and will load it with data up until 2020. Here is that structure:

Read on for examples of usage.  This is an example where thinking relationally differs from thinking procedurally—imagining date ranges as pre-calculated sets isn’t intuitive to procedural developers, but it can give a big performance boost.

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Parallelism Strategies For Grouping Operations

Published 2018-07-13 by Kevin Feasel

Itzik Ben-Gan continues his series on grouping data in SQL Server by looking at how these operations can go parallel:

Besides needing to choose between various grouping and aggregation strategies (preordered Stream Aggregate, Sort + Stream Aggregate, Hash Aggregate), SQL Server also needs to choose whether to go with a serial or a parallel plan. In fact, it can choose between multiple different parallelism strategies. SQL Server uses costing logic that results in optimization thresholds that under different conditions make one strategy preferred to the others. We’ve already discussed in depth the costing logic that SQL Server uses in serial plans in the previous parts of the series. In this section I’ll introduce a number of parallelism strategies that SQL Server can use for handling grouping and aggregation. Initially, I won’t get into the details of the costing logic, rather just describe the available options. Later in the article I’ll explain how the costing formulas work, and an important factor in those formulas called DOP for costing.

As you will later learn, SQL Server takes into account the number of logical CPUs in the machine in its costing formulas for parallel plans. In my examples, unless I say otherwise, I assume the target system has 8 logical CPUs. If you want to try out the examples that I’ll provide, in order to get the same plans and costing values like I do, you need to run the code on a machine with 8 logical CPUs as well. If you’re machine happens to have a different number of CPUs, you can emulate a machine with 8 CPUs—for costing purposes—like so:

DBCC OPTIMIZER_WHATIF(CPUs, 8);

Even though this tool is not officially documented and supported, it’s quite convenient for research and learning purposes.

This is a fairly long article, but a great one.

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Installing Confluent Platform On Windows

Published 2018-07-12 by Kevin Feasel

Niels Berglund shows how to install Confluent Platform (the Confluent branded version of Apache Kafka) on a Windows machine using the Windows Subsystem for Linux:

WSL is primarily aimed at developers, and it allows you to run Linux environments directly on Windows in a native format and without the overhead of a virtual machine. Let us retake a look at that statement: run Linux environments directly on Windows in a native format. Yes native format, WSL is not a UNIX-like environment like Cygwin, which wraps non-Windows functionality in Win32 system calls but it serves Linux programs as special, isolated minimal processes (pico-processes) attached to kernel-mode pico-providers. If you want to read all the “gory” details about WSL: Windows Subsystem for Linux Overview gives you an excellent introduction.

Surprisingly, it’s pretty easy—I would have expected some strange compatibility issues.

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Building Cone Plots In Plotly

Published 2018-07-12 by Kevin Feasel

The Plotly blog shows how to use Python to build 3D cone plots using Plotly:

This plot uses an explicitly defined vector field. A vector field refers to an assignment of a vector to each point in a subset of space.

In this plot, we visualize a collection of arrows that simply model the wind speed and direction at various levels of the atmosphere.

3-D weather plots can be useful to research scientists to gain a better understanding of the atmospheric profile, such as during the prediction of severe weather events like tornadoes and hurricanes.

Sometimes a 3D plot is the best answer.  When it is, this looks like a good solution.  H/T R-bloggers

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Using APPLY To Aggregate Unpivoted Data

Published 2018-07-12 by Kevin Feasel

Dan Clemens gives us yet another practical use of the APPLY operator:

I had a situation last week where I needed to find the MIN() and MAX() values of some data. Normally this would be pretty straightforward, but the problem was I needed to identify the MIN() and MAX() values amongst multiple columns. So today I bring you a SQL tip using APPLY.

Looking at sys.procedures we can see I have a create_date and a modify_date column for each record. What if we needed to return the MIN() or MAX() value from those 2 (or more) columns?

SELECT [Name]
,create_date
,modify_date
FROM sys.procedures AS p
WHERE p.[name] = 'ChangePassword';

In this two-column example, it’s not too difficult.  As you add more and more columns, the solution remains the same, though the urge to ask why all of these dates are unpivoted might increase…

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