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Category: T-SQL Tuesday

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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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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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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Checking File Sizes In SQL Server

Published 2018-07-12 by Kevin Feasel

Andy Mallon looks back at a contribution by Junior DBA Andy, this one on checking file sizes:

This is every DBA’s favorite game. Figuring out what DMV contains the data you want. It turns out there are two places that database file size info is maintained. Each database has sys.database_files which has information for that database. The master database also has sys.master_files, which contains information for every database.

Using sys.master_files seems like it would be the obvious choice: everything in one view in master is going to be easier to query than hitting a view in a bunch of different databases. Alas, there’s a minor snag. For tempdb, sys.master_files has the initial file size, but not the current file size. This is valuable information, but doesn’t answer the use cases we set out above. I want to know the current file sizes. Thankfully, sys.database_files has the correct current file sizes for tempdb, so we can use that.

Using sys.database_files seems like it’s going to be the right move for us then. Alas, this isn’t quite perfect either. With Log Shipping, and Availability Group secondaries, if you’ve moved data files to a different location, sys.database_files will contain the location of the files on the primary database. Thankfully, sys.master_files has the correct local file locations for user databases, so we can use that.

Ugh, so it looks like the answer is “both”… we’ll need to use sys.database_files for tempdb, and sys.master_files for everything else.

Click through for the script, including Andy’s critical reflection on how Past Andy has failed him.

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Adding IN Search Functionality To .NET

Published 2018-07-12 by Kevin Feasel

Jay Robinson shows off a few extension methods he creates to make dealing with C# easier:

Then I could use the extension like this:

if (mySeries.In(Enum.Series.ProMazda, Enum.Series.Usf2000)) myChassis = "Tatuus";

As for the other two methods, well… When is a null not a null? When it’s a System.DBNull.Value, of course! SQL Server pros who have spent any time in the .NET Framework will recognize this awkwardness:

var p = new System.Data.SqlClient.SqlParameter("@myParam", System.Data.SqlDbType.Int);
p.Value = (object)myVar ?? System.DBNull.Value;

With the extension, the second line becomes:

p.Value = mVar.ToDbNull();

I like it that Jay ended up going with a different language than T-SQL.  It’s no F#, but it’ll do.

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Finding Low-Hanging Fruit When Tuning SQL Server

Published 2018-07-12 by Kevin Feasel

Kevin Hill has a couple scripts which help him find easy performance gains:

Recently, I’ve been getting a lot of performance tuning work, much of which is basically “things are slow…can you fix them?” type of requests.  Most experienced DBAs know that there a few gazillion factors that can lead to this request, and I won’t re-hash them here.

Lets assume, that we’ve optimzed or eliminated the server, disks, network, etc. and were now looking at SQL code and everyone’s favorite – indexes.

I have two scripts I use that give me a quick overview of the type of work SQL Server is doing.   These complement each other, and are used AS A STARTING POINT to locate the low-hanging fruit that can be causing excessive work for the disks and memory of the server.

Click through for those scripts.

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Generating Index Drop And Create Statements

Published 2018-07-11 by Kevin Feasel

Drew Furgiuele says “Game over, man, game over!” to indexes:

The premise is simple: it will generate a series of DROP and then CREATE INDEX commands for every index. The process is a little more complex in practice, but at a high level it:

  1. Creates a special schema to house a temporary object,
  2. Creates a special stored procedure to run the code,
  3. Calls said stored procedure,
  4. Generates a bunch of PRINT statements that serve as the output (along with new line support for readability),
  5. Cleans up the stored procedure it generated,
  6. And finally deletes the schema it created.

Nifty.

Click through for the script, as well as a bonus Powershell script.  Because hey, it’s only six lines of code.

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Instance-To-Instance Migrations With Start-DbaMigration

Published 2018-07-11 by Kevin Feasel

Chrissy LeMaire touts one of the best parts of dbatools:

dbatools is such a fun toolset to work on, but specifically, I can no longer live without Start-DbaMigration. Even in smaller shops, migrations are often required and they are always a lot of work.

At least they used to be, before I built the command that started it all: Start-DbaMigration. Start-DbaMigration is an instance to instance migration command that migrates just about everything. It’s really a wrapper that simplifies nearly 30 other copy commands, including Copy-DbaDatabase, Copy-DbaLogin, and Copy-DbaSqlServerAgent.

Also a bonus shout out to dbachecks.

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Gathering Info On Tables

Published 2018-07-11 by Kevin Feasel

Raul Gonzales has a script which provides useful information for tables and columns:

Useful information it provides at table level:

  • tableType, to identify HEAP tables
  • row_count, to identify tables with plenty of rows or now rows at all
  • TotalSpaceMB, to identify big tables in size
  • LastUserAccess, to identify tables that are not used
  • TotalUserAccess, to identify tables that are heavily used
  • TableTriggers, to identify tables that have triggers

Useful information it provides at column level:

  • DataType-Size, to identify supersized, incorrect or deprecated data types

  • Identity, to identify identity columns

  • Mandatory-DefaultValue, to identify NULL/NOT NULL columns or with default constraints

  • PrimaryKey, to identify primary key columns

  • Collation, to identify columns that might have different collation from the database

  • ForeignKey-ReferencedColumn, to identify foreign keys and the table.column they reference

Click through for the script.

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The Best Of The Underground Toolbox

Published 2018-07-10 by Kevin Feasel

Adrian Buckman shares some of his favorite creations:

sp_AGreconfigure

This is a great goto proc for an alternative to the Always on availability group GUI for changing Failover mode, Synchronous mode or even Readable options.

When you manage multiple servers with multiple Availability groups this stored procedure can save you alot of time, sometimes I find the GUI can take a long time to open but equally it can take some time to execute the command.

sp_AGreconfigure can speed this process up for you, we tend to use this as our goto for switching synchronous settings when patching/rebooting replicas but also I tend to use it in @Checkonly = 1 mode for giving the Availability group settings a once over.

Click through for this and several other useful tools.

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