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Month: April 2016

Object Naming

Published 2016-04-06 by Kevin Feasel

Andy Galbraith warns you against…odd…database names:

I went and looked on the server, and sure enough in Management Studio I saw one database named “FinanceDB” and a database named “[FinanceDB]”.

This was on a SQL 2008R2 instance, but as a test I created a database named [test] on my local SQL 2014 instance and sure enough it worked!

The source of the problem at the client was the LiteSpeed maintenance plan.  Even though the backup task was set to backup all user databases, it wasn’t picking up the square-bracketed database.

I’d go a bit further and say that you should avoid everything but alpha-numeric characters and maybe underscore for databases, tables, views, and all other database objects.

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M Query Timing

Published 2016-04-05 by Kevin Feasel

Chris Webb gives a couple of options for timing M queries:

In M, the DateTime.LocalNow() function returns the current system date and time at the time the function is called – which means that you could call it multiple times in the same query and get different results. There’s also the DateTime.FixedLocalNow() function which also returns the system date and time; the difference between the two is, as the documentation says:

This value is fixed and will not change with successive calls, unlike DateTime.LocalNow, which may return different values over the course of execution of an expression.

This is good to know for those query-tuning scenarios.

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B-Tree Indexes

Published 2016-04-05 by Kevin Feasel

Derik Hammer is starting a new series on index types and has started with the venerable B-tree:

On more than one occasion I have been told that the B-Tree index is the index structure which was designed after the A-Tree index. Another common misconception is that it stands for Binary-Tree. As logical as those may seem, they are false. The ‘B’ in B-Tree does not actually have any specific meaning. Check out Ed McCreight’s explanation here (16:08) where he admits that the name discussion was never settled.

In its most basic form, the B-Tree index is a hierarchy of data pages (page structures lightly touched on in the next post of this series). The lowest level is called the leaf level, the highest level is the index root, and all levels in between are the intermediate levels. This structure is an improvement over the Binary Tree index because its balanced nature greatly improved the performance of maintenance operations such as, INSERT, DELETE, and UPDATE.

On the terminological point, I’d always heard that the “B” stood for “Balanced” because of the level flatness—in contrast to a “normal” tree, you wouldn’t have more than a pre-defined number of levels separation (usually one) between leaf nodes.

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A Tribute To SQL 2005

Published 2016-04-05 by Kevin Feasel

Brent Ozar gives his tribute to SQL Server 2005:

I remember the first time I used SQL Server 2005.

I was a database administrator working on a new-build data warehouse project in Miami. Both our data warehouse and SQL Server 2005 were looking like they were going to come out at the same time, and I kept hoping I could make the timing work.

SQL Server 2005 looked so seductive. Let’s take just a moment to think back about all the cool new technologies it introduced:

SQL Server 2005 was, in my opinion, the first enterprise-quality version of SQL Server.  2000 was a great start but wasn’t quite there yet.  This version, though, was quite nice.

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Circular References

Published 2016-04-05 by Kevin Feasel

Daniel Hutmacher looks at circular references in recursive CTEs:

Suppose you have a tree hierarchy where (among other members) “3” is the parent of “8”, “8” is the parent of “B” and “B” is the parent of “E”. You could easily draw this as a branch structure where the members could be profit centers of a company, divisions of government, managers and employees, product lines, cell references in an Excel sheet or pretty much anything that can be described as a hierarchy.

3
--8 --B --E

Now, if we say that “E” is the parent of “3”, we’ve created a circular reference, and we end up with an infinite recursion. What that means is that if you follow the tree from the root to the leaf level, you’ll end up going round and round in circles. In terms of a database query, that means that the query will go on forever until it either fills up your log file or tempdb, or until the maximum number of recursions (OPTION MAXRECURSION) is reached, whichever happens first.

I did something similar a while back with foreign key dependencies.  Because foreign key relationships are potentially cyclical graphs, they can easily fall into the same scenario.

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SQL Server Marketplace Images

Published 2016-04-05 by Kevin Feasel

Melissa Coates debates whether to use a SQL Server marketplace image for an Azure VM:

As more and more customers are interested in moving some portion of their BI/analytics workloads to cloud services, one question that comes up occasionally is whether or not you should start with a marketplace image that has SQL Server already installed. So far I’ve noted a few key considerations for this decision:

  1. Do you want to pay for the SQL Server license as part of the VM pricing?

  2. Do you want to configure SQL Server in a specific way (i.e., following best practices)?

  3. Do you want Azure to handle things like automated patching by default?

My rule of thumb is if it’s Express Edition or just for me to mess around with, I’m typically happy with an image.  But for a production setup, I’d want the fine-grained control at installation time that you just won’t get.

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File Processing Pattern

Published 2016-04-05 by Kevin Feasel

Bill Fellows describes a pattern for processing files in an ETL scenario:

All ETL processing will use a common root node/directory. I call it SSISData to make it fairly obvious what is in there but call it as you will. On my dev machine, this is usually sitting right off C:. On servers though, oh hell no! The C drive is reserved for the OS. Instead, I work with the DBAs to determine where this will actually be located. Heck, they could make it a UNC path and my processing won’t care because I ensure that root location is an externally configurable “thing.” Whatever you’re using for ETL, I’m certain it will support the concept of configuration. Make sure the base node is configurable.

A nice thing about anchoring all your file processing to a head location is that if you are at an organization that is judicious with handing out file permissions, you don’t have to create a permission request for each source of data. Get your security team to sign off on the ETL process having full control to a directory structure starting here. The number of SSIS related permissions issues I answer on StackOverflow is silly.

It comes down to consistency and cleanliness.  Plan ahead and you’ll have a much nicer go of things.  Bill also provides a Biml POC, so check that out as well.

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Drop Column In SQL Server 2012/2014

Published 2016-04-04 by Kevin Feasel

Aaron Bertrand explains a bug in SQL Server 2012 and 2014 which can crop up after dropping a column:

A fix has been published for SQL Server 2012 (SP2 and SP3), and one is coming for SQL Server 2014 (RTM and SP1) – though in this most recent update, SQL Server 2014 was removed from the list of affected versions (not sure it was accurate to remove those). I will update this space once the next 2014 CUs are released, but for now you should plan to rebuild tables after dropping columns as a matter of course and, more importantly, as part of the same maintenance operation.

This is a good reason to stay up to date on CUs.

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Jupyter Notebooks With R

Published 2016-04-04 by Kevin Feasel

Andrie de Vries notes that Azure Machine Learning now supports Jupyter Notebooks with R:

I wrote about Jupyter Notebooks in September 2015 (Using R with Jupyter Notebooks), where I noted some of the great benefits of using notebooks:

  • Jupyter is an easy to use and convenient way of mixing code and text in the same document.

  • Unlike other reporting systems like RMarkdown and LaTex, Jupyter notebooks are interactive – you can run the code snippets directly in the document

  • This makes it easy to share and publish code samples as well as reports.

Jupyter Notebooks is a fine application, but up until now, you could only integrate it with Azure Machine Learning if you were writing Python code.  This move is a big step forward for Azure ML.

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Transitioning To Extended Events

Published 2016-04-04 by Kevin Feasel

Dave Mason shares his story of moving from Profiler traces to Extended Events:

Thinking back, my initial reaction was probably something like “I don’t get it.”. XEvents just seemed like a new dog performing an old trick. Even though I concluded most of the SQL pros had already made the transition to Extended Events (XEvents), and that I’d be living in the past if I didn’t do the same, I continued to use Profiler. It’s too bad–my current employer at the time had SQL 2012 across the board. I missed a great opportunity there. Before I left that job, I stumbled upon this Paul Randal post. It helped me trouble-shoot a performance issue with a stored proc. “Ok, so there’s one thing XEvents can do that Profiler can’t do” I thought to myself. (Note: I don’t know if that’s a true sentiment or not–I never investigated further.) I also recall reading at least one of Jonathon Kehayias’ (b|t) posts about XEvents, but I don’t remember which one. Profiler would remain my go-to tool for the remainder of my time with that employer.

Read this in conjunction with Erin’s request.

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