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Month: May 2017

Joining Availability Groups

Published 2017-05-18 by Kevin Feasel

Chris Lumnah troubleshoots an error in automatic seeding of an Availability Group:

In my lab, I decided to play around with the automatic seeding functionality that is part of Availability Groups. This was sparked by my last post about putting SSISDB into an AG. I wanted to see how it would work for a regular database. When I attempted to do so, I received the following error:

Cannot alter the availability group ‘Group1’, because it does not exist or you do not have permission. (Microsoft SQL Server, Error: 15151)

Read on for the answer; it turns out automatic seeding itself was not the culprit.

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Disabling Nested Loop Join Optimization

Published 2017-05-18 by Kevin Feasel

Dmitry Pilugin explains the differences between trace flag 2340 and the DISABLE_OPTIMIZED_NESTED_LOOP query hint:

This optimization provides a great boost with a sufficient number of rows. You can read more about its test results in the blog OPTIMIZED Nested Loops Joins, created by Craig Freedman, an optimizer developer.

However, if the actual number of rows is less than the expected one, then CPU additional costs to build this sort may hide its benefits, increase CPU consumption and reduce its performance.

Read the whole thing.  I think the likelihood of using either this hint or the trace flag is near nil, but crazy things do come up.

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Multi-Statement Functions

Published 2017-05-18 by Kevin Feasel

Erik Darling has started looking at interleaved execution of multi-statement table-valued functions in SQL Server 2017.  First, he gives an intro:

In the first plan, the optimizer chooses the ColumnStore index over the nonclustered index that it chose in compat level 130.

This plan is back to where it was before, and I’m totally cool with that. Avoiding bad choices is just as good as making good choices.

I think. I never took an ethics class, so whatever.

In part deux, Erik compares interleaved multi-statement functions to in-line table-valued functions:

In this case, the inline table valued function wiped the floor with the MSTVF, even with Interleaved Execution.

Obviously there’s overhead dumping that many rows into a table variable prior to performing the join, but hey, if you’re dumping enough rows in a MSTVF to care about enhanced cardinality estimation…

Just like Global Thermonuclear War, I believe the best way to win mutli-statement versus inline TVFs is not to play at all.

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Apache Solr Backup And Recovery

Published 2017-05-17 by Kevin Feasel

Hrishikesh Gadre shows how to back up indexes in Apache Solr:

The backup mechanism allows an administrator to create a physically separate copy of index files and configuration metadata for a Solr collection. Any subsequent change to a Solr collection state (e.g. removing documents, deleting index files or changing collection configuration) has no impact on the state of this backup. As part of disaster recovery, the restore operation creates a new Solr collection and initializes it to the state represented by a Solr collection backup.

It’s probably safest to treat data in Solr as secondary data, in the sense that you should be able to rebuild the entire data set from scratch instead of Solr being a primary data store.  I’m not a big fan of the author using the term “disaster recovery” instead of just “recovery” or “backup restoration” (as they’re different concepts), but it’s worth the read.

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Getting Get-Help Help

Published 2017-05-17 by Kevin Feasel

Shane O’Neill troubleshoots a problem and explains how helpful Get-Help can be in the process:

Why does help exist?

When you think about it, why is there even a function called help?
As far as I’m aware it’s basically the same as Get-Help except it automatically pipes the output to | more so we get pages rather than a wall of text.

Is there more that we can do with Get-Help though? Is there a way that we can return the examples only? Syntax only? Parameters only?

Is there not a way that we can do such things?!

Read on to find out if there is.

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SQL Server Updates For MacOS

Published 2017-05-17 by Kevin Feasel

Meet Bhagdev has a couple MacOS-related announcements for SQL Server.  First, the SQL Server team has released command line tools:

We are delighted to share the production-ready release of the SQL Server Command Line Tools (sqlcmd and bcp) on macOS El Capitan and Sierra.

The sqlcmd utility is a command-line tool that lets you submit T-SQL statements or batches to local and remote instances of SQL Server. The utility is extremely useful for repetitive database tasks such as batch processing or unit testing.

The bulk copy program utility (bcp) bulk copies data between an instance of Microsoft SQL Server and a data file in a user-specified format. The bcp utility can be used to import large numbers of new rows into SQL Server tables or to export data out of tables into data files.

Second, there’s a new ODBC driver available:

  • Azure AD support – You can now use Azure AD authentication (username/password) to centrally manage identities of database users and as an alternative to SQL Server authentication.

  • Always Encrypted support – You can now use Always Encrypted. Always Encrypted lets you transparently encrypt the data in the application, so that SQL Server will only handle the encrypted data and not plaintext values. Even if the SQL instance or the host machine is compromised, an attacker gets ciphertext of the sensitive data.

  • Table Valued Parameters (TVP) support – TVP support allows a client application to send parameterized data to the server more efficiently by sending multiple rows to the server with a single call. You can use the ODBC Driver 13.1 to encapsulate rows of data in a client application and send the data to the server in a single parameterized command.

Multi-platform is the catchword of the day.  If you’re a MacOS user, this might be a portent of things to come.

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Pester For Presentations

Published 2017-05-17 by Kevin Feasel

Rob Sewell takes Pester to the edge:

If you have PowerShell version 5 then you will have Pester already installed although you should update it to the latest version. If not you can get Pester from the PowerShell Gallery follow the instructions on that page to install it. This is a good post to start learning about Pester

What can you test? Everything. Well, specifically everything that you can write a PowerShell command to check. So when I am setting up for my presentation I check the following things. I add new things to my tests as I think of them or as I observe things that may break my presentations. Most recently that was ensuring that my Visual Studio Code session was running under the correct user. I did that like this

Rob’s scenario is around giving presentations, but while reading this, think about those services which should be running on your SQL Server instance—the same concept applies.

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An Introduction To “Modern Excel”

Published 2017-05-17 by Kevin Feasel

Rob Collie explains how he talks about “Modern Excel,” by which he means DAX + Power Query/Power Pivot:

So the magic of Power Query is instantly apparent and tangible to basically any Excel Pro.  They can immediately see how PQ will save them oodles of time and anguish.

The benefits of DAX and relationships, by contrast, are less readily-apparent on first glance.  Portable/re-useable formulas that enable rapid iteration, the answering of “emergent” questions in near real-time, as well as a “subdivide and segment” capability?  Or how about multi-data-table capabilities that provide an integrated and convenient view across many different sources of formerly-siloed data?  These concepts are simply alien to the longtime Excel user, even though they are MONSTERS in terms of their biz value (as well as time-savers and anguish-reducers).  None of the impact “lands” up front because it can’t adequately be contemplated until you’ve started DOING it.

Rob’s looking at this from the standpoint of an educator helping train people with Excel expertise.

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Against Shrinking Database Log Files

Published 2017-05-17 by Kevin Feasel

Kenneth Fisher is wary of shrinking your database log file:

It’s too big
I find that people who say this frequently don’t have a firm idea of what is too big or even why it might be as big as it is. This also goes in with the I need to free up disk space with no good reason why the space needs to be freed up.

There are good reasons to shrink the log and they do revolve around space. For example:

  • I had a one-time explosive growth of the log due to a large data load.

  • The usage of the database has changed and we aren’t using as much of the log as we used to.

  • We are billed at 2 am based on space used. We will grow the log back again after the billing period.

  • I need to clean up a large number of VLFs. (of course, then you are going to grow it back manually right?)

I quoted the caveats but Kenneth makes a solid case against shrinking log files without a good counterbalancing reason.

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Which Write- Cmdlet Should I Use?

Published 2017-05-17 by Kevin Feasel

Jana Sattainathan has some thoughts on when to use each of the Write- cmdlets in Powershell:

PowerShell has matured as the automation tool of choice on the Microsoft platform, be it on Windows or Azure. However, there is no official guidance on best-practices and standards around some things. At times, bloggers do things incorrectly in their examples thereby reinforcing bad practices. Hopefully, this small post will help connect some dots for you! Please comment if I am stating something that is not a generally accepted best practice. Specifically, we are going to glance at the following cmdlets

  • Write-Host

  • Write-Output

  • Write-Debug

  • Write-Warning

  • Write-Error/Throw

  • Write-Verbose

  • Write-Progress

Write-Host is the easiest and probably most controversial of the set (because its messages are outside the pipeline), but there’s a place for each of these.

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