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Month: August 2018

The Blocking Monitoring Framework

Published 2018-08-02 by Kevin Feasel

Dmitri Korotkevitch announces a new tool:

Troubleshooting of the blocking and concurrency issues is, in the nutshells, a simple process. You need to identify the processes involved in blocking conditions or deadlocks and analyze why those processes acquire the locks on the same resources. In majority of cases, you need to analyze queries and their execution plans identifying possible inefficiencies that led to excessive number of locks being acquired.

Collecting this information is not a trivial task. The information is exposed through DMVs (you can download the set of scripts here); however, it requires you to run the queries at time when blocking occurred. Fortunately, SQL Server allows you to capture blocking and deadlock conditions with the blocked process report and deadlock graph, analyzing them later.

There is the caveat though. Neither blocked process report nor deadlock graph provide you execution plans of the statements. Nor do they always include affected statements in the plain text. You may need to query plan cache and other DMVs to get this information and longer you wait lesser is the chance that the information is available. Moreover, SQL Server may generate enormous number of blocked process reports in cases of prolonged blocking and complex blocking chains, which complicates the analysis.

Confirmed to work with SQL Server 2012 and later, but might work on earlier versions as well.  Dmitri has released it to the public, so check it out.

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In Defense Of Inline Table-Valued Functions

Published 2018-08-02 by Kevin Feasel

Riley Major defends the honor of inline table-valued functions:

So no, user-defined functions are not the devil. Scalar user-defined functions can cause big problems if misused, but generally inline user-defined functions do not cause problems.

The real rule of thumb is not to avoid functions, but rather to avoid adorning your index fields with logic or functions. Because when you hide your intentions from the optimizer with complex syntax, you risk not getting the better performing index seek.

Riley shows an example where his inline table-valued UDF was just as efficient an execution plan as without the UDF.

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Things Not To Do In SQL Server

Published 2018-08-02 by Kevin Feasel

Randolph West has a how-not-to guide for SQL Server:

Don’t use TIMESTAMP

We covered this in detail in a previous post, What about TIMESTAMP? It’s better to pretend that this data type doesn’t exist.

Why not?

It is not what you think it is. TIMESTAMP is actually a row version value based on the amount of time since SQL Server was started. If you need to record an actual date and time, use DATETIME2 instead.

When should we?

Never.

I appreciate that Randolph includes a “when should you not listen to my overall pronouncement?” bit, as there are commonly exceptions to “do not do X” style rules.

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Joining Streams Of Data

Published 2018-08-01 by Kevin Feasel

Chuck Blake gives an example of joining two streams of data together in Wallaroo:

The joining event streams pattern takes multiple data pipelines and joins them to produce a new signal message that can be acted upon by a later process.

This pattern can is used in a variety of use cases. Here are a few examples:

  • Merging data for an individual across a variety of social media accounts.

  • Merging click data from a variety of devices (e.g. mobile and desktop) for an individual user.

  • Tracking locations of delivery vehicles and assets that need to be delivered.

  • Monitoring electronic trading activity for clients on a variety of trading venues.

Conceptually, it’s very similar to normal join operations, but there is a time element which complicates things.

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Confluent Platform 5.0 Released

Published 2018-08-01 by Kevin Feasel

Raj Jain and Michael Noll walk through the latest version of Confluent Platform, Confluent’s Kafka solution:

With Confluent Platform 5.0, operators can secure infrastructure using the new, easy-to-use LDAP authorizer plugin and can deliver faster disaster recovery (DR) thanks to automatic offset translation in Confluent Replicator. In Confluent Control Center, operators can now view broker configurations and inspect consumer lag to ensure that they are getting the most out of Kafka and that applications are performing as expected.

We have also introduced advanced capabilities for developers. In Confluent Control Center, developers can now better understand the data in Kafka topics due to the new topic inspection feature and Confluent Schema Registry integration. Control Center presents a new graphical user interface (GUI) for writing KSQL, making stream processing more effortless and intuitive as well. The latest version of KSQL itself introduces exciting additions, such as support for nested data, user-defined functions (UDFs), new types of joins and an enhanced REST API. Furthermore, Confluent Platform 5.0 includes the new Confluent MQTT Proxy for easier Internet of Things (IoT) integration with Kafka. The latest release is built on Apache Kafka 2.0, which features several new functionalities and performance improvements.

Looks like there have been some nice incremental improvements here.

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Testing BI Projects With NBi: Hierarchies And Levels

Published 2018-08-01 by Kevin Feasel

Cedric Charlier shows us a potential pain point when testing an Analysis Services cube with hierarchies defined:

When executing the following query (on the Adventure Works 2012 sample database/cube), you’ll see two columns in the result displayed by SSMS. It’s probably what you’re expecting, you’re only selecting one specific level of the hierarchy [Date].[Calendar Date] and one measure.

You’re probably expecting that NBi will also consider two columns. Unfortunately, it’s not the case: NBi will consider 4 columns! What are the additional and unexpected columns? The [Date].[Calendar].[Calendar Year] and [Date].[Calendar].[Calendar Semester] are also returned. In reality, this is not something specific to NBi, it’s just the standard behaviour of the ADOMD library and SSMS is cheating when only displaying one column for the level!

Click through for the solution.  And if NBi sounds interesting, check out Cedric’s prior post on the topic.

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Configuring SQL Operations Studio

Published 2018-08-01 by Kevin Feasel

Kendra Little gave a quiz on SQL Operations Studio and is now sharing the answers:

Question 2: To toggle a BLOCK comment, the built-in shortcut is…

Answer: Shift+Alt+A

  • Correct: 43 (27%)
  • Incorrect: 118 (73%)

I think a lot of folks who use SSMS regularly and don’t use VSCode may not know what I meant by the question, because SSMS doesn’t have this functionality (or if it does, I’ve never figured out the shortcut!)

Check out all of the answers and build up those SQLOps skills.

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Betteridge’s Law And Index Hints

Published 2018-08-01 by Kevin Feasel

Bert Wagner asks a question in his title, Should You Use Index Hints?  Those familiar with Betteridge’s Law of Headlines know the general answer already:

One way to “fix” a poor performing plan is to use an index hint.  While we normally have no control over how SQL Server retrieves the data we requested, an index hint forces the  query optimizer to use the index specified in the hint to retrieve the data (hence, it’s really more of a “command” than a “hint”).

Sometimes when I feel like I’m losing control I like using an index hint to show SQL Server who’s boss.  I occasionally will also use index hints when debugging poor performing queries because it allows me to confirm whether using an alternate index would improve performance without having to overhaul my code or change any other settings.

About the only place I consistently use index hints is with filtered indexes, where the combination of parameter sniffing and inexactitude in filters will convince the optimizer that the filtered index isn’t helpful when it really is.

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Database Source Control With SVN

Published 2018-08-01 by Kevin Feasel

Nate Johnson sets up SVN for local source control:

I almost always have trouble remembering which option is for use with a non-empty folder of “here’s a bunch of files that I want to dump into the repo to start with”, vs. “here’s an empty folder where I want to pull down the contents of an existing repo”.  Fortunately, Tortoise yells at you if you try to do the latter — which is Export — into a non-empty folder.  So we want to Import.  Assuming you have a folder where all your SQL scripts live already, right-clicky and say “Tortoise SVN .. Import.”

Check it out.  The only concern I have is that this source control is just local source control.  That’s very helpful in situations where you accidentally mess something up, but my preference is to put my code in the same source control system the developers are using.  And if the developers aren’t using source control, get that institution in place as soon as possible because that’s begging for trouble.

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