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Category: Administration

Getting Row Counts After Execution

Published 2020-05-19 by Kevin Feasel

Grant Fritchey gives us a few ways to find row counts after a query has finished:

But, if you really want to get picky, batches and procedures frequently have multiple statements. This means that the row count you’re getting isn’t for a particular table. If you want to get that, then you need to capture the statement level stuff, sp_statement_completed or sql_statement_completed, depending on if you’re looking at procedures or batches.

However, this is one of those “be careful what you wish for” moments. Because, if you capture all statements in a system, you’re going to have a very large amount of data to deal with. This is where filtering is your friend.

Click through for Grant’s full answer.

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Handling Cross-Database Transactions

Published 2020-05-18 by Kevin Feasel

Michael J. Swart explains how cross-database transactions work on a single instance:

The transaction is touching two different databases. So it makes sense that the two actions should be atomic and durable together using the one single transaction.

However, databases implement durability and atomicity using their own transaction log. Each transaction log takes care of its own database. So from another point of view, it makes sense that these are two separate transactions.

Which is it? Two transaction or one transaction?

Click through to read the article, and then check the comments for a cautionary tale around database mirroring and cross-database transactions.

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Solving Last Page Contention Problems

Published 2020-05-18 by Kevin Feasel

Erik Darling ponders several techniques for solving the last page contention problem in SQL Server:

If one dare go looking, a list of Microsoft Approved™ solutions for dealing with last page contention exists.

I’m going to walk through my experiences with them in different scenarios, so you get a better understanding of which ones work best, and which ones can be tough to implement.

Read the whole thing.

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Removing and Refilling All Tables in a Database

Published 2020-05-18 by Kevin Feasel

Phil Factor has a couple T-SQL scripts for us to remove and reload a test database:

Copying a database using a BCP dataset from a DOS script or from PowerShell is fairly quick and trivial, but what if the data is already in another copy of the database on the same instance? Imagine you have a database build that is a copy of an existing database on the same instance and you want to run a ‘destructive’ test on the data, and do it over and over again.

Deleting all the data in a database should, you’d have thought, be trivial. Truncation doesn’t work because it doesn’t like to truncate tables with foreign keys, even if they are disabled. DELETE is safer but you will need to then reset any identity columns. Deleting large tables in one chunk isn’t scalable, so you have to do it in smaller chunks. I like to disable triggers while I do this as well. The only disadvantage comes if you have triggers that are supposed to be disabled because the simple code just re-enables them all.

This is, I think, one of the biggest selling points for containers where the database is built into the container image. You spin up a container based off of an image, perform your destructive testing, and destroy the container afterward. The next time you need to run these tests, spin up a new container. And if you need to change the data, modify the container. This introduces new challenges like how SQL Server on Linux has limitations which don’t exist on Windows, but for supported functionality, it’s a nice solution.

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Finding the SQL Server Service Account with T-SQL

Published 2020-05-14 by Kevin Feasel

Andy Mallon gives us a way in SQL to find the service account used for SQL Server:

SQL Server 2005 introduced Dynamic Management Views(DMVs). Technically, there are both views & functions–DMVs & DMFs, but colloquially they’re often simply referred to as just “DMVs”. DMVs simply return information about the state of the server or database and can be used for monitoring and troubleshooting of server/database health & performance.

New DMVs are added all the time. Today, let’s take a look at one of those useful DMVs.

This won’t cover all of the services—for example, it does not include the PolyBase engine or data movement service accounts—but it will give you some of the most important ones.

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Taking the Pulse of Your Azure VM

Published 2020-05-14 by Kevin Feasel

Mark Broadbent has put together a quick Powershell script to figure out what’s going on with an Azure VM:

I was recently given the task of identifying the state of an Azure VM so that an automation script using the az vm run-command invoke would not fail if the VM was down or under a reboot.

I initially thought the task would be really easy and a simple query of the VM state using Get-AzVM would provide us with a running state property of the VM, but as it happens the state is a little abstracted.

Click through to see how Mark solved the challenge.

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Who and What is Using Your tempdb Space?

Published 2020-05-14 by Kevin Feasel

Guy Glantser helps us troubleshoot who is using tempdb space and for what purpose:

In the past two weeks I encountered 3 different scenarios in which tempdb has grown very large, so I decided to write about troubleshooting such scenarios.

Before I describe the methods for troubleshooting tempdb space usage, let’s begin with an overview of the types of objects that consume space in tempdb.

The answer, of course, was Professor Plum in the Aviary with the eager spool.

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Thread Pool Exhaustion and Availability Groups

Published 2020-05-13 by Kevin Feasel

Sean Gallardy lays down the gauntlet:

You’re probably wondering why you couldn’t spawn a new thread, why this error happened, why you shouldn’t just up the max worker threads, and probably also thinking this must be some kind of “bug” in SQL Server. So here’s where our awkward conversation starts… It’s you. Contrary to every relationship breakup you’ve ever had, it’s definitely you. I’m not saying this to be mean but to really drive the point home here. The major reasons for this occurring are large blocking chains, too much workload for the server size (databases, users, etc.), and/or your virtual infrastructure sucks. There aren’t too many reasons for getting yourself into this situation, and while what I’ll be putting forth here isn’t exhaustive of all edge cases and scenarios, these are by far the majority of all the items in the wild that I’ve either worked on or have been involved in at some level. Side Note: If you’ve read this far, are shaking your head, calling me names that an irate sailor might utter, and telling yourself that upping the max worker threads as the product error suggests and Microsoft should fix their bugs then you can stop reading here as you’re probably not open to learning why you have issues in your environments.

One more scenario I’ve seen is mirroring thousands of databases on a single instance. That scenario fit none of Sean’s criteria—there was very little blocking, most of the databases were small and infrequently-used, and the infrastructure was the right size. It was just a huge number of databases and each database requiring a minimum of X worker threads. Mind you, it was still a bad idea…

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Capturing CHECKDB Output

Published 2020-05-13 by Kevin Feasel

Erin Stellato shows how you can track the results of those automated CHECKDB runs you’re doing:

First, you need to be running CHECKDB on a regular basis.  If you’re going to ask what you mean by regular basis, I’ll direct you to a post of Paul’s that is still relevant: Importance of running regular consistency checks.  There are a few factors to consider, but in general I recommend at least once a week.  If you’re a 9 to 5 shop and have the maintenance window to run CHECKDB daily, feel free to do that.

Erin walks us through it and also recommends checking out Ola’s scripts for integrity checks. I’d add to that Minion CheckDB.

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Understanding Memory Grants

Published 2020-05-12 by Kevin Feasel

Taiob Ali walks us through the concept of memory grants:

DesiredMemory: Memory estimated to fit intermediate results in KB for the chosen degree of parallelism. If the query runs in serial mode, this is the same as SerialDesiredMemory.

(Amount needed to store all temporary rows in memory. This depends on the cardinality estimate, expected number rows and average size of row). This is called additional because a query can survive lack of such memory by storing part of temporary rows on hard disk. A query is not guaranteed to have the full amount if the total exceeds the preset limit.)

Read on for explanations of each of the elements in MemoryGrantInfo.

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