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Month: March 2016

LDF Stamp Change

Published 2016-03-23 by Kevin Feasel

The CSS SQL Server engineering team points out that the LDF stamp has changed from 0x00 to 0xC0:

Question:  If the log is stamped with 0xC0’s instead of 0x00’s how is it a performance gain?

Many of the new hardware implementations detect patterns of 0x00’s.   The space is acquired and zero’s written to stable media, then a background, hardware based garbage collector reclaims the blocks.

This is a very interesting background article which shows an integration pain point between the database platform and the storage platform.

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Filled Maps In Power BI

Published 2016-03-23 by Kevin Feasel

Reza Rad digs into filled maps in Power BI:

I’ve mapped suburbs to County because that was the lowest level I’ve found in data category for geographic information. (Place and Address cannot be used for Filled Map at the time or writing this post). and I got Nothing! Not event a small area on the map.  I’ve tried then removing the district and putting suburb, region, country format with County as the data category which didn’t helped again.

I’ve found that I can map some locations based on Postal Code as you see below. However not Postal Code is not always good distinguishing field for a region, as multiple regions might have a postal code shared.

Filled maps have the potential to be powerful tools, but they aren’t perfect.  Check out Reza’s post for the full scoop.

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U-SQL Movie Recommender

Published 2016-03-22 by Kevin Feasel

Dave Ballantyne introduces us to U-SQL via a movie recommender:

What follows is an overview of my experiments that i have published into a GitHib repo. The “Examples” folder are what i would term “simple learnings” and “Full Scripts” are scripts that to a lesser or greater extent do something “useful”.  Im also not suggesting that anything here is “best practice” or method A performs better than method B,  I simply do not have the required size of data to make that call. My aim was to learn the language.

TLDR: Check out the script MovieLens09-CosineSimilarityFromCSVWithMax.usql for a U-SQL movie recommender.

U-SQL was introduced last year, but word of mouth about the language has been quite limited to date.  I’ll be interested in seeing what other examples pop up over the next few months.

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Local Aggregation

Published 2016-03-22 by Kevin Feasel

Niko Neugebauer investigates a new line in the Columnstore Index Scan execution plan tooltip, Actual Number of Locally Aggregated Rows:

There is a new line in the properties of the iterator, showing the number of locally aggregated rows and that number equals 619255, that should be exactly the number of rows that is missing from the arrow connecting 2 iterators:

Gives us our perfect 12627608 rows.
Eureca!
Is there any more information on this operation?
Indeed, just right-click on the Columnstore Index Scan and select it’s properties:

This is tied to some columnstore performance improvements in SQL Server 2016.

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Reorganize Columnstore Indexes

Published 2016-03-22 by Kevin Feasel

I have a new script available to reorganize columnstore indexes:

Note that this script requires SQL Server 2016 (or later) because the database engine team made some great changes to columnstore indexes, allowing us to use REORGANIZE to clear out deleted rows and compact row groups together, as well as its previous job of marking open delta stores as available for compression.

The code is available as a Gist for now, at least until I decide what to do with it.  Comments are welcome, especially if I’m missing a major reorganize condition.

As mentioned, comments are welcome.

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Generating Fixed-Width Files With Power Query

Published 2016-03-22 by Kevin Feasel

Chris Webb shows how to generate fixed-width files using Power Query inside Excel:

While it’s fairly common to need to load fixed-width files using Power Query or Power Query (and there’s a nice walkthrough of how to do this here), occasionally you might want to use Power Query and Excel to create a fixed-width output for another system, or maybe to create some test data. You might not want to do it often but I can imagine that when/if Power Query is integrated into SSIS this will be a slightly less obscure requirement; at the very least, this post should show you how to use a couple of M functions that are under-documented.

I don’t see this being a particularly common request, but I guess I can see some scenario in which we’re loading data into a legacy system.

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Trusting Foreign Keys

Published 2016-03-22 by Kevin Feasel

Jefferson Elias describes the concept of trusted foreign keys as well as their analog:

Specifying WITH CHECK in a statement tells to SQL Server the user wants it to validate the constraint against every single row in the table, then, if successful, enable it.

In contrast, specifying WITH NOCHECK, which is the default for an existing constraint, means that the constraint is enabled but no validation has been made on it. Even if this mode is faster to run, it can lead to severe side effects on performance: SQL Server doesn’t trust the constraint as it has not validated it. We refer to such a foreign key as an « untrusted foreign key ». As a consequence, the query optimizer won’t use the constraint to do his job…

There are benefits to having trusted foreign key constraints.  Check out the article for more details as well as how to fix this issue.

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Encrypt Your Connections

Published 2016-03-21 by Kevin Feasel

John Martin shows that part of securing your environment includes encrypting SQL Server connections:

In order to demonstrate just how easy it can be to get hold of the information inside the TDS packets I will be using Network Monitor from Microsoft, this will capture the network packets sent and allow me to see the details of what is being sent. Other tools such as Wireshark will also provide a level of insight into what is being sent between the application and SQL Server. I have configured three Windows Server 2012 R2 systems, one with the client (SQLCMD), one with SQL Server, and finally one which will act as a router between the two subnets that each server is on. This configuration can be seen below;

Wireshark is a good friend of mine.  It should be a good friend of yours, too, but only if your environment allows you to have a packet capture tool installed.

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Introduction To Tableau

Published 2016-03-21 by Kevin Feasel

Melissa Yu gives us an introduction to Tableau:

Do you know the difference between a blue pill and a green pill? What happens when you add a green pill to the color shelf? Pills, cards, and shelves are the foundation of Tableau visualizations. If you are new to Tableau or have been playing around with it but not quite sure how to get the view to look the way you want, we have a video for you!  In this video, I’ll help you understand pills, cards, and shelves so instead of wondering “Why did Tableau do THAT?” you’ll be in better control of what you want Tableau to do.

Power BI and Reporting Services 2016 are exciting technologies, but there’s a wide world outside of Microsoft, and Tableau is a major player in the world of visualization.

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