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Category: Administration

So You Want to Fail Over a SQL Managed Instance

Published 2020-08-12 by Kevin Feasel

Danimir Ljepava takes us through user-initiated failover of SQL Managed Instances:

In August 2020, we have released a new feature user-initiated manual failover allowing to manually trigger a failover on SQL Managed Instance using PowerShell or CLI commands, or through invoking an API call.

Manually initiated failover on a managed instance will be an equivalent of the automated failover for high availability and software patches initiated automatically by the service. Manually invoking a failover on MI will help test end-to-end applications for fault resiliency on automatic failovers in case of planned or unplanned events before deploying to production. In addition to testing how failover impacts existing database sessions, it can also help verify if it changes the end-to-end performance due to changes in the network latency. In some cases if performance issues are encountered on SQL MI, manually invoking a failover to a new node can help mitigate the performance issue.

Read on to see how you can perform failover and how you can confirm that it worked.

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Learning from a Hadoop Outage

Published 2020-08-11 by Kevin Feasel

Sandhya Ramu and Vasanth Rajamani have an after-action report:

For companies and organizations, failure tends to be far more illuminating than success and the lingering effects of a failure can be harmful if the team moves too quickly and does not resolve the issue in a thorough and transparent manner. We recently ran into a large incident that involved data loss in our big data ecosystem and by reflecting on our diagnosis and response, we hope that our learnings from an impactful incident in our big data ecosystem will be insightful.

Here’s what happened: roughly 2% of the machines across a handful of racks were inadvertently reimaged. This was caused by procedural gaps in our Hadoop infrastructure’s host life cycle management. Compounding our woes, the incident happened on our business-critical production cluster.

Read on to understand what happened and why. It’s a lesson in the importance of having a disaster recovery plan and testing it

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Stopping and Starting Virtual Machines in a Resource Group

Published 2020-08-11 by Kevin Feasel

Dennes Torres walks us through a script to stop or start all virtual machines in an Azure resource group:

Some tasks on azure are easier if we automate them. The Azure Portal provides us the cloud shell, which we can use for this kind of automation.

I was making some experiences with SQL Server Always On, so I created three VMs inside a resouce group. Every time I want to start some experiment I need to start all three VMs and, in the end, stop all three again.

Read on to see how Dennes is able to accomplish this.

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Fixing Availability Group Issues with Alerts

Published 2020-08-07 by Kevin Feasel

Wayne Sheffield automates a few problems away:

The first of the Availability Group issues to discuss is that, for whatever reason, data is no longer moving between the primary replica and a secondary replica. This puts the Data Movement in a Suspended state.

If the data movement remains suspended for too long, you might have to take some undesired actions to get things back in sync. Things like removing the database from the AG, restoring log files, then reattaching it to the AG. When the data movement becomes suspended, we want to get it flowing again as soon as possible. Let’s have SQL Server try to get the data flowing again.

Read on for more, including a second issues that Wayne helps solve.

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Reviewing the Windows Event Log with Powershell

Published 2020-08-05 by Kevin Feasel

Jess Pomfret takes us through an improvement to the old Get-EventLog cmdlet:

Recently I was tasked with troubleshooting an incident on a SQL Server at a certain point in the past, the issue being a high CPU alert.  It’s hard (without monitoring solutions set up) to go back in time and determine what the issue is.  However, one thing we can check is the windows event log to see if there was anything happening on the server at that time.

Now, you probably know that my favourite tool of choice is PowerShell, so let’s take a look at how we can use Get-WinEvent to see what was happening in the past.

Get-WinEvent is the newer revamped version of Get-EventLog, and there are two improvements I believe are worth mentioning. Firstly, with the introduction of filter parameters we can now find certain events much easier, which we’ll talk about a little later. Secondly, the performance of Get-WinEvent is much faster than using the legacy command.  I believe this is due to the filtering happening at the event engine instead of within PowerShell.

Those are some rather welcome improvements.

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Enabling SQL Server Optimizer Hotfixes

Published 2020-08-03 by Kevin Feasel

John Morehouse takes us through the step-by-step for enabling optimizer hotfixes in SQL Server:

There are a number of knobs and switches that are available to database administrators that can be used to enable better performance.  There are three options in particular that this blog will be discussing, trace flag 4199, the database scoped configuration QUERY_OPIMIZER_HOTFIXES and the qeury hint ENABLE_QUERY_OPTIMIZER_HOTFIXES. Understanding how these options function will give you a hand up on ensuring the query optimizer is running as optimally as possible.

Let’s take a look at the three options.

Read on to learn more. There is some potential risk of regression with new optimizer updates, so standard rules around testing apply.

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Halloween Problem and Inserts

Published 2020-07-30 by Kevin Feasel

Jared Poche continues a dive into the Halloween Problem:

I would have expected us to scan the temp table, then have a LEFT JOIN to the base table. The Table Spool is the red flag that we have an issue with the plan, and is frequently seen with Halloween protections.

The index scan on the base table seems to be overkill since we’re joining on the primary key columns (the key lookup isn’t much of a concern). But we’re likely doing the scan because of the spool; it’s SQL Server’s way of getting all relevant records in one place at one time, breaking the normal flow of row mode operation, to make sure we don’t look up the same record multiple times.

Read on to see the execution plan as well as Jared’s fix.

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Working with SQL Server Configuration Files

Published 2020-07-29 by Kevin Feasel

Jamie Wick takes us through an underrated part of the SQL Server installer:

The ability to use a parameter file (configurationfile.ini), for automating the installation of SQL Server, has been around for many years. However, each release of SQL Server has had different parameters that could be included in the file. Here are some directions on how to find or create a parameter file, along with the parameter values that are supported by each version of SQL Server.

I appreciate the fact that every installation of SQL Server generates one of these and even points it out to you as you go through the installer wizard. And Jamie has gone a step further by giving us an Excel spreadsheet with all of the available settings and their defaults.

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Enforcing Database Practices with Policy-Based Management

Published 2020-07-27 by Kevin Feasel

Nisarg Upadhyay hits on one of my favorite features Microsoft doesn’t care about anymore:

In this article, I am going to explain how we can enforce the SQL database best practices using Policy-Based Management. The policy-based management feature of SQL Server was introduced in SQL Server 2005. This feature was useful because it helps database administrators to define and enforce the database policies based on the organizations’ requirements.

Back when I was a DBA, I really appreciated Policy-Based Management. Unfortunately, although my job has changed a few times since then, Policy-Based Management hasn’t.

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Finding and Downloading SQL Server Updates

Published 2020-07-22 by Kevin Feasel

Andy Levy combines dbatools and KBUpdate:

Another of Chrissy LeMaire’s (blog | twitter) projects is KBUpdate. Compared to dbatools it’s a pretty compact module, but it’s incredibly useful – it’ll seek out information about KB updates and even download them for you! She’s also rolled these functions into dbatools for convenience, so we don’t need to install or import that module separately.

Read on to see how Andy ties it all together.

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