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Author: Kevin Feasel

The Power Of DBCC CLONEDATABASE

Published 2016-08-30 by Kevin Feasel

Erin Stellato hacks DBCC CLONEDATABASE and makes it that much more powerful:

Very often when I mention testing before an upgrade, I’m told that there is no environment in which to do the testing.  I know some of you have a Test environment. Some of you have Test, Dev, QA, UAT and who knows what else. You’re lucky.

For those of you that state you have no test environment at all in which to test, I give you DBCC CLONEDATABASE. With this command, you have no excuse to not run the most frequently-executed queries and the heavy-hitters against a clone of your database. Even if you don’t have a test environment, you have your own machine.  Backup the clone database from production, drop the clone, restore the backup to your local instance, and then test.  The clone database takes up very little space on disk and you won’t incur memory or I/O contention as there’s no data.  You will be able to validate query plans from the clone against those from your production database. Further, if you restore on SQL Server 2016 you can incorporate Query Store into your testing! Enable Query Store, run through your testing in the original compatibility mode, then upgrade the compatibility mode and test again. You can use Query Store to compare queries side by side! (Can you tell I’m dancing in my chair right now?)

Erin’s discovery makes CLONEDATABASE go from being an interesting tool to being outright powerful for handling upgrades.

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Surrogate Versus Natural Keys

Published 2016-08-30 by Kevin Feasel

Kenneth Fisher digs into the debate on surrogate keys versus natural keys:

A natural key is one constructed of data that already exists in the table. For example using latitude and longitude in a table of addresses. Or the social security number in a table of employees. (Before you say anything, yes, the social security number is a horrible primary key. Be patient.)

My personal preference is to use surrogate keys most of the time and put unique constraints (or unique indexes) on the natural key.  There are some occasions in which I’d deviate, but ceteris paribus I’d pick this strategy..

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Azure SQL Data Warehouse Plans

Published 2016-08-30 by Kevin Feasel

Grant Fritchey shows how to build an execution plan for an Azure SQL Data Warehouse query:

So now we just save this as a .sqlplan file and open it in SSMS, right?

Nope!

See, that’s not a regular execution plan, at all. Instead, it’s a D-SQL plan. It’s not the same as our old execution plans. You can’t open it as a graphical plan (and no, not even in that very popular 3rd party tool, I tried). You will have to learn how to read these plans differently because, well, they are different.

That’s an unfortunate outcome.  Reading is hard…

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Start-Demo With Multi-Line Commands

Published 2016-08-30 by Kevin Feasel

Rob Sewell has an update to the Start-Demo cmdlet, making it no longer require backticks when running multi-line commands:

Start-Demo was written in 2007 by a fella who knows PowerShell pretty well 🙂 https://blogs.msdn.microsoft.com/powershell/2007/03/03/start-demo-help-doing-demos-using-powershell/

It was then updated in 2012 by Max Trinidad http://www.maxtblog.com/2012/02/powershell-start-demo-now-allows-multi-lines-onliners/

This enabled support for multi-line code using backticks at the end of each line. This works well but I dislike having to use the backticks in foreach loops, it confuses people who think that they need to be included and to my mind looks a bit messy

I’m going to need to look into Start-Demo; I’m not sure I’ve seen it before.

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Registering U-SQL Assemblies

Published 2016-08-29 by Kevin Feasel

Michael Rys shows how to register an assembly in the U-SQL catalog:

While the ADL Tools in VisualStudio make it easy to register an assembly, you can also do it with a script (in the same way that the tools do it for you) if you are for example developing on a different platform, have already compiled assemblies that you just want to upload and register. You basically follow the following steps:

You upload your assembly dll and all additionally required non-system dlls and resource files into a location of your choosing in your Azure Data Lake Storage account or even a Windows Azure Blob Store account that is linked to your Azure Data Lake account. You can use any of the many upload tools available to you (e.g., Powershell commands, VisualStudio’s ADL Tool Data Lake Explorer upload, your favorite SDK’s upload command or through the Azure Portal).

 

  1. Once you have uploaded the dlls, you use the CREATE ASSEMBLY statements to register them.

We will use this approach in the spatial example below.

There’s quite a bit going on in this post, making it an interesting read.

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Power BI Line Charts

Published 2016-08-29 by Kevin Feasel

Reza Rad digs into line charts:

Value Line

Line chart can show one or more measures as measures, such as Sales Amount, Total Costs, Quantity of the goods sold and etc.

Trend Line

Depends on the variety of values across a time period, Line chart can illustrate a straight line as a trend. This trend is good to understand how in overall products are selling, is revenue going up or down for example.

Reference Line

You might want to define minimum, maximum, average, or median values for your line chart as separate lines, and compare values lines with these lines. These are reference lines which can be dynamically created based on value of measures in the chart.

I think this was a rather helpful post in figuring out what Power BI is capable of doing, although if you build a lot of charts that look like Reza’s last example, you probably want to scale that back a bit.

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Ambari Metrics Collector Error

Published 2016-08-29 by Kevin Feasel

Jon Morisi had to troubleshoot an issue with the Ambari metrics collector not starting:

Last week I had a bit of a trial by fire:
“Here’s a 7 node, Hortonworks Hadoop cluster, metrics is broken, fix it, go!”

The initial indication that metrics was broken was apparent in the Services tab for Ambari Metrics.  Here it showed that there was an error and that Metrics Collector was Stopped.  The error however wasn’t very informative:

Connection failed: [Errno 111] Connection refused…

That didn’t tell me much at all, and neither did googling.
(I hope the title of this blog helps someone else find this solution quicker.)

Jon includes the answer and some additional helpful details.  Check it out.

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Live Query Stats Progress Changes

Published 2016-08-29 by Kevin Feasel

Pedro Lopes mentions that the latest version of Live Query Stats in SSMS 2016 has some improvements:

Below the finished query. Again, overall query execution cannot go over 100%, but at the operator level, percentages are shown as the real ratio between actual and estimated rows, with no caps.

So you can see how the actual rows from the clustered index scan on PhoneNumberType table was 14500% above estimations, and how a series of severe misestimations are coming from the bottom right area of the plan (where actual is not even 1% of estimated rows), worsening as it goes up in the nodes.

I think this makes Live Query Stats a better tool for query analysis.  I haven’t used it much in production, but this makes me want to give it another try.

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Running CheckDB On Log Shipping Subscribers

Published 2016-08-29 by Kevin Feasel

Brent Ozar shows how to support running DBCC CHECKDB on a log shipping subscriber:

 

At first glance, if you set up log shipping the way most folks do, it looks like you can’t run CHECKDB on a subscriber:

On SQL Server Enterprise Edition, you can try working around it by creating a database snapshot – but that won’t work either:

Here’s the trick: your database needs to be in standby mode instead of norecovery. When you run restores with the standby option, you’re able to query the database in between restores.

This doesn’t obviate the need for running CHECKDB on a primary, but it can offload some of that work some of the time.

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CISL 1.3.1

Published 2016-08-29 by Kevin Feasel

Niko Neugebauer has released the newest version of his columnstore index library:

Here is the small description of what is new in this release:

  • The database snapshots (.dacpac) for all platforms are now included in the Releases\DacPacs.

  • Includes new Powershell functions for installing and removing CISL from the Instances:

    • Install-CISL.ps1 will allow you to install the CISL at multiple databases of a SQ Server Instance (or Azure SQLDB).
    • Remove-CISL.ps1 will allow you to remove the CISL from the multiple databases of a SQL Server Instance (or Azure SQLDB).

  • Support for the different collation is included.

  • Includes information on all recent SQL Server updates.

  • Included support of the new Columnstore Indexes Trace Flags in SQL Server 2016.

  • Basic Unit Tests (based on t-sqlt) are included for SQL Server 2012 & SQL Server 2014, guaranteeing the quality of the released code.

  • A good number of bug fixes.

  • Further parameter enhancements for the existing functions.

Sounds like there’s a lot packed into this release.

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