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Author: Kevin Feasel

Extended Events and Query Store

Published 2020-03-12 by Kevin Feasel

Jason Brimhall takes us through some of the internals of Query Store as exposed by Extended Events:

One of my favorite questions to ask during some of presentations on XE is “What was the first version of SQL Server to have Query Store?” You can imagine the wide array of answers but what is interesting is how often  the correct answer is always missed. I hear lots of answers for 2012, some answers for 2017 and somewhere in between for 2016. But never does the correct answer pop up.

Right now, I hope you are scratching your head at that last statement. You see, the question is somewhat of a trick question. The first version of SQL Server that has QDS is SQL Server 2014. However, the first version where you can actually use it is SQL Server 2016. This fun fact is visible when we start exploring SQL Server from the realm of XE. Let’s take a look.

Read the whole thing.

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Preparing for Demos with Pester

Published 2020-03-12 by Kevin Feasel

Jess Pomfret has some advice for you if you ever give a presentation:

If you don’t know what Pester is, it’s a test framework for PowerShell.  In the simplest explanation, using their Domain-Specific Language (DSL) you describe how things should look. If all looks good it returns output in green and if it doesn’t you get red output.  There are a lot of great use cases for Pester, like using it to ensure your code does what it’s supposed to, using it to validate your SQL Server environment (dbachecks), or in this example using it to make sure your demos are setup and ready to go.

When I’m preparing for a presentation I go through the demos over and over again, so it’s easy to accidentally leave things in a state that will cause issues when I go to do my demos in the presentation. If you’re creating a table, for example, during the demo and you already created it practicing and then forgot to drop it, the demo gods will strike and it’ll fail when it matters most! A simple Pester test to check whether the table exists will solve this issue.

Even if you aren’t giving talks in public (or inside your company), Pester is a useful tool for ensuring that the thing you expect to be the case actually is the case.

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Oracle’s Automatic Workload Repository Explained

Published 2020-03-12 by Kevin Feasel

Kellyn Pot’vin-Gorman explains to us what the Automatic Workload Repository is:

The Automatic Workload Repository, (AWR) had been around since Oracle 10g and requires the diagnostic and tuning management pack licensing to use all of its features in Oracle’s Enterprise Edition database. Versions before 10.2.0.4 had limited collections vs. the modern reporting schema and every subsequent release of Oracle has added to it’s content, which explains the size increase stored in the objects/number of objects in the SYSAUX tablespace.

By default and since version 11.2.0.4, the AWR retention is 8 days and takes an automatic snapshot once per hour. It’s common for DBAs to up this retention to at least 31 days to capture a month of workload information and these snapshot identifiers can then be used to identify workload intervals for querying and reporting. Oracle can be also be configured to lessen the intervals between snapshots to change the granularity of the AWR reports, or my preference, the DBA or privileged user can take manual snapshots to identify an important beginning or ending of a period.

Kellyn goes into a good amount of detail in this post and, based on the title, promises at least a part 2. Though this could be a History of the World: Part I trick Kellyn is playing on us.

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Power BI Security Features

Published 2020-03-12 by Kevin Feasel

James Serra takes us through different ways to secure your Power BI dashboards and reports:

Row-Level Security: With Row-level security (RLS) you are given the ability to publish a single report to your users but expose the data differently to each person. So instead of creating multiple copies of the same report in order to limit the data, you can just create one report that will only show the data the logged in user is allowed to see. This is done with filters, which restrict data access at the row level, and you define filters within roles. For example, creating a role called “United States” that filters the data in a table where the Region = “United States”. You then add members (user, security group, or distribution list) who can only see data for the United States to the “United States” role (the assignment of members can only be done within the Power BI Service). If a user should not have access to a report, then just don’t include that person in any of the roles for that report, so they would always see a blank report.

Click through for several more options and links to additional resources.

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From IDENTITY to Sequences

Published 2020-03-12 by Kevin Feasel

Andy Levy recommends checking out sequences:

The SEQUENCE object eliminates all of this. It gives you a simple way to just grab a new number and increment for the next caller. It’s very fast as there’s no visible table I/O, and it’s unaffected by rollbacks.

And it’s so much easier to use! You just ask for the next number in the sequence!

I like sequences, though the interesting thing is that 2020 me has created them a lot less frequently than 2012 me was sure I would. I’m glad they’re in the product, however.

One thing I should point out is that sequences are like identity columns in that you can have gaps due to user behavior, such as rolling back transactions. If you absolutely need gap-free sets of numbers, you’re back to Andy’s Method One, except everything has to be serializable and wrapped in explicit transactions.

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R 3.6.3 Now Available

Published 2020-03-11 by Kevin Feasel

David Smith takes a look at R 3.6.3:

On February 29, R 3.6.3 was released and is now available for Windows, Linux and Mac systems. This update, codenamed “Holding the Windsock“, fixes a few minor bugs, and as a minor update maintains compatibility with scripts and packages written for prior versions of R 3.6. 

February 29 is an auspicious date, because that was the day that R 1.0.0 was released to the world: February 29, 2000. In the video below from the CelebRation2020 conference marking the 20th anniversary of R, core member Peter Dalgaard reflects on the origins of R, and releases R 3.6.3 live on stage (at the 33-minute mark).

I’m holding out for R 4, though then I’ll have to wait to see when SQL Server will officially support it.

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Developing Shiny Apps in Databricks

Published 2020-03-11 by Kevin Feasel

Yifan Cao, Hossein Falaki, and Cyirelle Simeone announce something cool:

We are excited to announce that you can now develop and test Shiny applications in Databricks! Inside the RStudio Server hosted on Databricks clusters, you can now import the Shiny package and interactively develop Shiny applications. Once completed, you can publish the Shiny application to an external hosting service, while continuing to leverage Databricks to access data securely and at scale.

That’s really cool. Databricks dashboards are nice for simple stuff, but when you really need visualization power, having Shiny available is great.

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Using Query Store to Replay Workloads

Published 2020-03-11 by Kevin Feasel

John Sterrett shows us an unorthodox use of Query Store:

Today, I wanted to talk about my least favorite part of replaying workloads. It’s having an extended event or server-side trace running during a workload replay only so we can compare the results at a query-level when the replay is finished. Now, this might seem like a trivial thing but when you have workloads over 10k batch requests/sec this can consume terabytes of data quickly. The worst part is waiting to read all the data, slice and dice the data for analysis.

Starting with SQL Server 2016 there is a better and faster way to go! You can replace your extended event or server-side trace with Query Store captured data. Today, I will show you how to use the Query Store for the same purpose.

Click through for the solution.

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Adoption Patterns with Query Store

Published 2020-03-11 by Kevin Feasel

Erin Stellato has some thoughts on Query Store adoption:

Last fall we had a previous customer reach out for help after they had to wait 45 minutes for a database to come online after a server reboot. The database queries were blocked by QDS_LOADDB waits. There were three things in play here – the first was that they had CAPTURE_MODE set to ALL, and it should be AUTO. Second, they didn’t have trace flag 7752 enabled (the behavior of which is now the default in SQL Server 2019). And the third was that their Query Store was 100GB in size. The workload was fairly ad hoc, so these three things together caused the problem initially described. They implemented the TF, made multiple changes to the settings (set CAPTURE_MODE to AUTO, changed MAX_STORAGE_SIZE_MB to 10GB, decreased CLEANUP_POLICY to 3 days), and then Query Store was usable for them.

Read on for more examples.

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Query Store and Spinlocks

Published 2020-03-11 by Kevin Feasel

David Fowler takes a look at an issue with Query Store:

We moseyed on down to the server in question to take a look at it.  One thing stood out immediately, CPU was pegged out at 100% but SQL itself didn’t actually seem to be doing anything, transactionssecond was on the floor. Unfortunately this happened a while back and I didn’t think to capture any graphs or metrics at the time so you’re just going to have to take my word for this.

After looking into a few different things, the mention of spinlock contention came up.  I’ll be honest here, actual spinlock contention is rare and is something that I’ve seen cause an issue only a handful of times so it’s something that I don’t generally get to until I’ve ruled out just about everything else.

David’s scenario was on an older patch of SQL Server and it was fixed later. It’s a good reminder to keep those servers patched.

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