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Category: Administration

ASYNC_NETWORK_IO and Execution Plans

Published 2020-03-05 by Kevin Feasel

Jonathan Kehayias dives into an interesting problem:

A few weeks ago, an interesting question was asked on the #SQLHelp hash tag on Twitter about the impact of execution plans on the ASYNC_NETWORK_IO wait type, and it generated some differing opinions and a lot of good discussion.

My immediate answer to this would be that someone is misinterpreting the cause and effect of this, since the ASYNC_NETWORK_IO wait type is encountered when the Engine has results to send over TDS to the client but there are no available TDS buffers on the connection to send them on. Generally speaking, this means that the client side is not consuming the results efficiently, but based on the ensuing discussion I became intrigued enough to do some testing of whether or not an execution plan would actually impact the ASYNC_NETWORK_IO waits significantly.

To summarize: Focusing on ASYNC_NETWORK_IO waits alone as a tuning metric is a mistake. The faster a query executes, the higher this wait type will likely accumulate, even if the client is consuming results as fast as possible. (Also see Greg’s recent post about focusing on waits alone in general.)

Click through for the things Jonathan tested.

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Setting Up a SQL Server Lab with AutomatedLab

Published 2020-03-04 by Kevin Feasel

Jess Pomfret looks at a very interesting Powershell module:

There is a fantastic PowerShell module called AutomatedLab that can enable you to easily build out a lab for the  specific scenario you need to test. Even better is the module comes with 70 sample scripts that you can start with and adapt to meet your needs.

The module gives you the option to work with Hyper-V or VMWare. I will say most of the examples are using Hyper-V, and that is what I’ll be using also.

For my lab I want a SQL Server 2019 instance joined to a domain, and a separate client machine that I can manage the SQL Server from. On the client I would need to be able to connect to the internet as I want to be able to download PowerShell modules from the gallery easily.

It’s about time for me to rebuild my lab, so I’ll need to check that out.

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Capturing Query Errors with Extended Events

Published 2020-03-03 by Kevin Feasel

Jack Vamvas shows how to capture query errors using Extended Events:

If you’re troubleshooting SQL Server query errors , you’ll already know Extended Events are highly useful and very effective method to capture SQL Server errors.

To use the script you’ll need appropriate privileges to create the Extended Event. You will also need to have some space available on the disk to store output files.

If you want something a little less permanent, you can use the ring buffer target. I put together something like this a long time ago and enjoyed IM-ing coworkers and saying “You forgot the join criteria” with no other context. Freaked them out the first couple of times…

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Creating the Elastic Job Agent for Azure SQL Database

Published 2020-03-02 by Kevin Feasel

Kate Smith continues a series on Elastic Jobs in Azure SQL Database:

There is no way to create the Elastic Job Agent in T-SQL. I have already shown how to do this in PowerShell. To do this in the Azure Portal, go to Home, click the box that says “+ Create a Resource”, then search in the box for Elastic Job Agent. Select that, and then follow the steps in the portal to create the agent.

After creating the agent, Kate then shows how to set up credentials, target groups, and jobs.

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Removing an Extra Transaction Log File

Published 2020-03-02 by Kevin Feasel

Jeff Iannucci shows how to remove an unwanted guest from your database:

True, there’s no advantage to having more than one log file, but sometimes that one file grows suddenly and fills up the drive in the middle of a transaction and you’re stuck with those dreaded “THE DATABASE IS DOWN!!!” tickets until that transaction finishes. So, in the heat of the moment, you hit the panic button and create ANOTHER log file on a different drive.

Then, minutes, hours, or even weeks later, you want to put the universe back in order by resizing the original log file and removing the extra one. But what if you find you can’t remove that extra one, no matter what you try to do?

This is a legitimate case. Hopefully you plan ahead and never hit it, but stuff happens.

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Snapshot Creation in Azure Data Studio

Published 2020-03-02 by Kevin Feasel

Dave Bland checks out an extension to Azure Data Studio to manage snapshots:

Like many Azure Data Studio extensions, DB Snapshot Creator is designed to bring functionality into ADS that is not present by default.  This extension was developed by Sean Price. As the name suggests, this extension can be used to easily create database snapshots.  Before going too deep into this extension, let’s take a quick moment to go over what a snapshot is.

Back in the day, I created a WPF tool for a company to manage snapshots for manual testing: take a snapshot, perform whatever destructive testing you needed to do, and revert back to a known good state. In a world with good CI/CD tooling and Docker containers, that’s not nearly as important anymore, but sometimes you just need to run a quick test, so I’m glad the functionality is still around.

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Creating an Elastic Jobs Agent

Published 2020-02-27 by Kevin Feasel

Kate Smith continues a series on elastic jobs in Azure SQL Database:

Having laid the conceptual groundwork for Elastic Jobs in two previous postings (1, 2), I am now going to create an elastic job and associated credentials using PowerShell.  For this scenario, I have one or more databases with a table ‘T’ and statistics ‘tStats’. I want to enforce an update for these statistics every day. To do this, I need to check that my stats have been updated in the past day, and if not, update them. The T-SQL to update statistics on a table “T” with stats named “tStats” is simple:

Click through for the Powershell script.

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Finding Folder Sizes with Powershell

Published 2020-02-26 by Kevin Feasel

Jeffrey Hicks shows us a quick way to retrieve information on folder sizes:

It is simple enough to run Get-Childitem and pipe the results to Measure-Object.

But this can be often time consuming. The other drawbacks, besides typing is it takes extra work for format the results into something more user friendly. And if i want to include hidden files, I have to remember to use -Force with Get-ChildItem.

Cmdlets are nice and convenient. And I always recommend to beginner or even intermediate scripters, if there is a cmdlet to use over the .NET Framework, use the cmdlet. But there are always exceptions and as you grow in expertise, you’ll realize there are times when going directly to the .NET Framework is a better choice. Which is what I have done.

Click through for the solution.

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Managing Performance on Azure SQL Managed Instances

Published 2020-02-26 by Kevin Feasel

Tim Radney has a few considerations for you if you want to start using Azure SQL Managed Instances:

Storage is a bit more difficult to plan and make considerations for, due to having to consider multiple factors. For storage you need to account for the overall storage requirement for both storage size, and I/O needs. How many GBs or TBs are needed for the SQL Server instance and how fast does the storage need to be? How many IOPS and how much throughput is the on-premises instance using? For that, you must baseline your current workload using perfmon to capture average and max MB/s and/or taking snapshots of sys.dm_io_virtual_file_stats to capture throughput utilization. This will give you an idea of what type of I/O and throughput you need in the new environment. Several customers I’ve worked with have missed this vital part of migration planning and have encountered performance issues due to selecting an instance level that didn’t support their workload.

Tim has a lot of good advice in here, so read the whole thing.

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