VLFs

Tom Roush talks VLFs, changes in DBCC LOGINFO, and Availability Groups:

Turns out SQL 2008R2 (where the original script worked) returns different fields than 2012 and 2014 (where it didn’t).

I figured I didn’t want to find out which version of the script to use every time I needed to run it on a server, so I told the script to figure that out by itself, and then run the appropriate hunk of code (example below)

This is a good explanation of how to back out of a complex situation.

Change Azure SQL Database Compatibility Level

Tom LaRock shows us how to change the compatibility level of an Azure SQL Database:

You can change the compatibility level of an Azure SQL Database.

It’s true! I know!

OK, so I’m a little excited about this one. See, I’ve been giving this talk on cardinality for the past couple of years now, so this is a hidden gem to me. When I found out this was possible I took out my demo scripts to see if changing the compatibility level would have any effect.

This is interesting, especially given that Management Studio doesn’t give you that option.  Know your T-SQL, folks.

SQLQueryStress Source Code Now Available

Adam Machanic has made the SQLQueryStress source code publicly available:

So here’s the official word: The attached source code is hereby released to the world, copyright and royalty free. You may use it, if you like, for whatever you want. Enjoy! If you use it for a public project, I would appreciate a mention in the acknowledgements section, but even that is not required. This source code is yours, warts and all. I was tempted to do some cleanup work, but at this point it’s just not something I’m ever going to touch again. I upgraded the project from Visual Studio 2005 to Visual Studio 2013, confirmed that it builds and seems to work, and that’s that.

Adam may never have used in a production scenario, but I certainly have, and SQLQueryStress is still the best free load simulator.  There’s also a GitHub repo thanks to Erik Ejlskov Jensen, so go forth and hack at some C# code.

Anchor Modeling

Steph Locke has a presentation on Anchor Modeling as 6th Normal Form:

Anchor Modelling moves you beyond third normal form and into sixth normal form. What does this mean? Essentially it means that an attribute is stored independently against the key, not in a big table with other attributes. This means you can easily store metadata about that attribute and do full change tracking with ease. The historical problem with this methodology is that it makes writing queries a real pain. Anchor Modelling overcomes this by providing views that combine all the attribute data together.

Anchor Modeling is a rather different approach, so if it sounds interesting, check out the tutorial.

Analyzing World Running Times

Andrie de Vries looks at average speed for different mens’ running events:

However, it seems that there might be two kinks in the line:

  • The first kink occurs somewhere between the 800m distance and the mile. It seems that the sprinting distances (and the 800m is sometimes called a long sprint) has different dynamics from the events up to the marathon.

  • And then there is another kink for the ultra-marathon distances. The standard marathon is 42.2km, and distances longer than this are called ultramarathons.

The analysis is done in R, and the code is available in the post.  Check it out.

What Makes A Good Post?

Kevin Feasel

2016-01-05

Meta

Tony Davis tells us what makes for a compelling article:

As an author, it’s a mistake to make wild assumptions about what the reader already knows about the technology, and why it’s useful. Don’t just ‘show the rooms’, but explain why they are interesting and how they might be used.

Beyond these fundamentals, I’ve written before about the simple ‘rules’ for writing a compelling blog post, and of the need to avoid hyperbole, colloquialisms, and acronym-overload, in favour of simple, plain English that can be understood internationally.

I’ll take a moment to talk about what makes you likely to show up on Curated SQL.  My expected reader is someone who has a few minutes to kill during the day and is looking for technical content.  They might occasionally have more time to dig into interesting topics, but more frequently, I’m imagining somebody on a pre-lunch coffee break.  To make things easier for those readers, I’m looking for four things:

  1. Is the post concise?  Coffee breaks won’t last long enough to watch a webinar.  This is most flexible criterion; if it’s interesting but a bit lengthy, I’m still liable to include it.
  2. Is the post technical?  We’re geeks; we want to learn something even on coffee break.  Non-technical posts can be great, but they aren’t really in the Curated SQL purview.
  3. Is the post at least somewhat novel?  If I’ve linked to someone taking a cursory look at Querystore, I’m probably not going to link to another overview of that product unless there’s something new in there.  With that said, “novel” is a hard goal; what’s new to me might be old hat to you, so there’s a balancing act here.
  4. Is the post well-written?  Poor writing makes technical content more difficult to understand, so sometimes I’ll skip an otherwise-interesting technical post and wait for somebody else to post a better version.

With that said, I gladly accept submissions via Twitter (@curatedsql).

Trickle Migration

Richie Lee encountered a use case for trickle migration:

Recently I needed to apply compression data on a particularly large table. One of the main reasons for applying compression was because the database was extremely low on space, in both the data and the log files. To make matters worse, the data and log files were nowhere near big enough to accommodate compressing the entire table in one go. If the able was partitioned then I could have done one partition at a time and all my problems would go away. No such luck.

Best way to eat an elephant, etc. etc.  Read the whole thing; you might be in a similar situation someday.

Use Parentheses Wisely

Jen McCown plays around with the AND and OR operators:

Specifically, how is it evaluated when your where clause says “WHERE This AND That OR Something AND that”, without any clarifying parenthesis?

Let’s play around with this. The simplest test scenario is a SELECT 1. If I get a 1 back, that means my WHERE clause evaluated to true, right? Right.

Parentheses should clarify statements.  If I see an “AND” and an “OR” in a WHERE clause, I want to see parentheses, even if you’ve gotten it right.  It’s too easy to misinterpret precedence.

Think About Installation

Dave Mason implores us to think of the installation:

Every tsql command in your SQL script(s) has the potential to fail. It’s important to catch and handle tsql errors so that they don’t cause the entire installation to fail. This will require a lot of defensive, resilient, fault-tolerant coding on your part. Here’s an example for creating the database. Note the emphasis on permissions, which I touched on in another post.

This is important advice if you send installation scripts to customers (even if you’re using a packager to generate an install EXE).

Capturing Blocking Information

Erin Stellato shows us how to capture details when processes are blocked:

To view the output from extended events you can open the .xel file in Management Studio or query the data using the sys.fn_xe_file_target_read_file function. I typically prefer the UI, but there’s currently no great way to copy the blocking report text and view it in the format you’re used to.  But if you use the function to read and parse the XML from the file, you can…

If you can’t buy a tool which monitors long-term blocking, you can still build it yourself pretty easily.

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