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Category: Administration

Resumable Online Index Rebuilds

Published 2017-04-24 by Kevin Feasel

Niko Neugebauer introduces a new feature in SQL Server 2017:

After multiple executions, the first process (Resumable Online Index Rebuild) on the average took 65.8 seconds, while the second one (a simple online) took only 60.8 seconds, representing 8% of the improvement of the overall performance. I can’t say if it looks acceptable to you or not, but for me this is something I will be definitely considering to be as an advantage for the cases where the resumable process is needed.

I decided to run a test on much bigger table, the lineitem which for 10GB TPCH database contains 60 Million Rows. My expectation here was to see if the percentage would stay the same or will jump to a whole new level (please make sure that you do execute the following script at least a couple of times, to get the real results and not the results of your disk-drive prefetching :)):

The big table example result was somewhat surprising.  Niko is his normal, informative self, so definitely read the whole thing.

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Upgrading SQL On Linux

Published 2017-04-21 by Kevin Feasel

Steve Jones has a post on upgrading SQL Server on Linux:

I’m cutting off part of the path, since I think it’s probably NDA. No worries, apparently the old location for me hasn’t been updated with new packages, which makes sense.

I decided to check the MS docs and see how a new user would get SSoL running? At the new docs.microsoft site, I found the Install SQL Server on Ubuntu doc.

Following the instructions, I updated the GPG keys and registered the repository with curl:

curl https://packages.microsoft.com/keys/microsoft.asc | sudo apt-key add -

curl https://packages.microsoft.com/config/ubuntu/16.04/mssql-server.list | sudo tee /etc/apt/sources.list.d/mssql-server.list

My expectation is that upgrading SQL Server on Linux is going to be a lot less painful than upgrading on Windows.

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Blob Auditing For Azure SQL Database

Published 2017-04-21 by Kevin Feasel

Patrick Keisler shows how to use Blob Auditing with Azure SQL Database to log database activity:

If you have multiple objects or actions to audit, then just separate them with a comma, just like the AuditActionGroups parameter. The one key piece to remember is you must specify all audit actions and action groups together with each execution of Set-AzureRmSqlDatabaseAuditingPolicy. There is no add or remove audit item. This means if you have 24 actions to audit and you need to add one more, then you have to specify all 25 in the same command.

Now let’s run a few queries to test the audit. First, we’ll run a simple select from the Salaries table.

Patrick shows off the UI (which is nice for one-off checking) and also the function sys.fn_get_audit_file(), which you’d probably want to use for automated audit checks.

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Dark Queries

Published 2017-04-19 by Kevin Feasel

Michael Swart helps root out queries which get recompiled frequently and so won’t be in the cache:

Some of my favorite monitoring solutions rely on the cached queries:

but some queries will fall out of cache or don’t ever make it into cache. Those are the dark queries I’m interested in today. Today let’s look at query recompiles to shed light on some of those dark queries that maybe we’re not measuring.

By the way, if you’re using SQL Server 2016’s query store then this post isn’t for you because Query Store is awesome. Query Store doesn’t rely on the cache. It captures all activity and stores queries separately – Truth in advertising!

Click through for an Extended Event session which looks for recompilation.

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Resetting SQL Administrators

Published 2017-04-19 by Kevin Feasel

Chris Lumnah shows how to use dbatools to reset a SQL authenticated administrative account:

As I was going through my environment, I realized I created a new domain controller for my tests. This DC has a new name and domain name which is different from my other VMs. I quickly realized that this will cause me issues later with authentication. No worries. I will just boot up the VMs and then and join them to the new domain. Easy-peasy. Now let met go test out my SQL Servers.

DOH!!

I received a login failure with access is denied. Using Windows Authentication with my new domain and recently joined server is not working. Why?…..Oh right, my new user id does not have access to SQL Server itself. As I sit there smacking myself in the head, I am also thinking about the amount of time it will take me to rebuild those VMs. Then it hit me!!!

Read on to see the solution, including a Powershell one-liner showing how it’s done.

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CPU Hot-Add And NUMA

Published 2017-04-17 by Kevin Feasel

Frank Denneman discusses VMware NUMA behavior when you hot-add more CPUs:

But what happens when the VM is configured with less vCPUs than the core count of the physical CPU package and CPU Hot-Add is enabled? Will there be performance impact? And the answer is no. The VPD configured for the VM fits inside a NUMA node, and thus the CPU scheduler and the NUMA scheduler optimizes memory operations. It’s all about memory locality. Let’s make use of some application workload test to determine the behavior of the VMkernel CPU scheduling.

For this test, I’ve installed DVD Store 3.0 and ran some test loads on the MS-SQL server. To determine the baseline, I’ve logged in the ESXi host via an SSH session and executed the command: sched-stats -t numa-pnode. This command shows the CPU and memory configuration of each NUMA node in the system. This screenshot shows that the system is only running the ESXi operating system. Hardly any memory is consumed. TotalMem indicates the total amount of physical memory in the NUMA node in kb. FreeMem indicates the amount of free physical memory in the NUMA node in kb.

Interesting reading.

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SQL Server Migration With dbatools

Published 2017-04-14 by Kevin Feasel

Garry Bargsley gives an example of how quickly you can migrate a SQL Server instance:

So in just 1 minute and 34 seconds you have migrated all of the following from one server to another.

  • All SP_Configure settings

  • Any Custom Error Messages

  • Any SQL Credentials

  • All Linked Servers

  • Database Mail along with Configuration and Profiles and Accounts

  • All user objects in System Databases

  • All Backup Devices

  • Any System Triggers

  • All User Databases

  • All Logins

  • Any Data collectors

  • Any Security Audits

  • All Endpoints, Policy Management, Resource Governor, Extended Events

  • And Finally All SQL Server Agent Jobs, Schedules, Operators, Alerts

These are probably very small databases (as it was a test instance), but dbatools is quite impressive.

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Be Wary Of Case Sensitivity

Published 2017-04-13 by Kevin Feasel

Slava Murygin points out that for SQL Server on Linux, case sensitivity matters a lot:

So, in that manner, SQL Server files will be located in “c:\var\opt\mssql\” directory!
Isn’t it simple?!!!
There will be no effort at all to refurbish old SQL SQL Server code for new Linux platforms!

Here I’ll give you an example of Database creation using different addressing methods:
1. I use Windows notation for data file and Linux notation for log file.
2. Because Linux systems are case sensitive it is very important to know it when you work with Linux. However, Microsoft allows you to be reluctant. You can use upper or lower case in the order you want.

Click through for an example.

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Optimizing For Ad Hoc Workloads

Published 2017-04-13 by Kevin Feasel

Kendra Little has soured a bit on the Optimize for Adhoc Workloads setting:

Once upon a time, I was really excited about getting this configuration item in SQL Server 2008. Early versions of SQL Server 2005 weren’t all that great at managing the size of the execution plan cache: it could really balloon up and eat away at the buffer pool. But the SQL Server team did a good job at tuning those algorithms in later service packs for 2005 and future versions, and it became much less of an issue.

Personally, I’ve never had a case where enabling ‘Optimize for Adhoc Workloads’ improved performance in a way that I could measure. It may save you a small amount of memory, it may not.

I don’t mean this as a big insult. Trying to save a penny every time you go to the grocery store could add up, if you grocery shop very frequently. But hopefully that’s not one of your major revenue sources over time.

It’s an interesting counter-argument and worth reading.

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Collations

Published 2017-04-07 by Kevin Feasel

Robert Sheldon has an article on collations:

The ideal solution is to choose a collation when setting up SQL Server that can be used for all your user databases and character columns. Using one collation removes any issues you might encounter when querying the data in different ways. It can also be the best approach in terms of performance if multiple collations impact your queries. However, this approach works only if the same language and collation settings are appropriate for all your users and applications—or at least a good majority of them.

If you support multi-cultural environments, you’ll need to take into account a number of considerations. To begin with, you should pick collations that support the most users, and you should use Unicode data types where possible because they can help avoid code page conversion issues. Just keep in mind the storage requirements that come with Unicode’s two bytes per character.

My inclination is to say Unicode everywhere possible.  There are cases in which Unicode doesn’t fit, but it’s easy to do and if you have enough data to worry about the extra bytes Unicode characters take up, Unicode compression is available.

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