SQL Server High Availability – DBCC 2021 – Part 1

Any one of my customers has asked, or should have asked, “do I need a certain level of high availability for my SQL server or one of my SQL servers?” Regrettably, these deliberations often come to a halt when it comes to the budget… Naturally, such HA-solutions are more expensive, and depending on the solution chosen and the environment’s configuration, appropriate licenses must be made available. However, if one calculates the costs that will occur in the “worst-case” scenario during or as a result of an outage, it should be clear that these costs are reversible.

I had the opportunity to give a speech about it last week at the Data Blaster Community Conference 2021 (thank you, SQLPASS Deutschland), and here is a summary of what I spoke about.

I’ve shown right from the start how high such costs can be, and I’ve done so with the help of a Percona online calculator. The SQL Server goes down for 1-2 hours, 5 employees are assigned to the Restore, each earning $100,000 per year, and 100 additional employees cannot work correctly, earning an average of $50,000 per year. In the following screenshot, you can see the numbers that can occur during an emergency, during recovery, or as a result of the trouble.

Why does SQLServer High Verfuegbarkeit matter? - Percona Calculator

With total costs of about 8.000.000 Euros for a 2 hour SQL Server outage, I’d consider spending an additional 250.000 Euros for the installation to add a second server and equip it with the required licenses. But, as I’ll explain in the following sections, such high availability can be seen in the SQL Server setup dialog, but first, let’s clear up the terminology… 😉

Disaster Recovery vs. High Availability

On wikipedia.de, the term “high availability” is described as follows:

High availability (HA) is a characteristic of a system that aims to ensure an agreed level of operational performance, usually uptime, for a higher than standard period.

https://en.wikipedia.org/wiki/High_availability

In comparison, the concept of disaster recovery.

Disaster Recovery assumes that the primary site is not recoverable (at least for some time) and represents a process of rebuilding data and services to a secondary survived site, which is opposite to restoring back to its original place.

https://en.wikipedia.org/wiki/Disaster_recovery

When it comes to high availability, it’s all about keeping the time of an outage or downtime as low as possible so that all connected systems can keep running as quickly as possible without data loss or manual intervention. Naturally, before the installation, you should think about the process design, the goals to be achieved, and the need.

  • What is the purpose of the business?
  • What would it cost the company if they are unable to work?
  • Is there, on the whole, a compromise between technology and business? Does it really have to be the minimum downtime (<10 seconds), or is it possible that maximum downtimes of less than a minute are sufficient?
  • What is it that technology can accomplish?
  • Knowledge, processes, and all those must all be followed to the letter of the law?

And only after these questions have been answered can you think about the actual solution for high availability and how it can/should be implemented.

The AlwaysOn Failover-Cluster (FCI)

High Availability - SQL Server - AlwaysOn Failover Cluster

We now come to one of the possible solutions for achieving high availability of SQL Servers inside your own datacenter, the Windows Failover Cluster (basically identical to a Linux Failover Cluster, but you should refer to the documentation of the respective distribution and cluster software).

Initially, a Windows Failover Cluster is created from two Windows Servers with the additional installed Failover-Cluster feature, or, to put it another way, both servers are logically (and in AD) connected. Both are familiar with one another and are now aware that they belong together, exchanging several relevant health-status information. This Windows Failover Cluster is given its own IP address and DNS name and a Cluster-Named-Object (CNO) in Active Directory, which later “manages” the cluster.

I can’t say anything about the required storage requirements because it varies depending on the environment… Whether it’s a SAN, NAS, NFS, HCI, or something else, it’s always about a storage system that can give both servers access. Microsoft adds the following:

Contrary to the availability group, an FCI must use shared storage between all nodes of the FCI for database and log storage. The shared storage can be in the form of WSFC cluster disks, disks on a SAN, Storage Spaces Direct (S2D), or file shares on an SMB. This way, all nodes in the FCI have the same view of instance data whenever a failover occurs. This does mean, however, that the shared storage has the potential of being the single point of failure, and FCI depends on the underlying storage solution to ensure data protection.

https://docs.microsoft.com/en-us/sql/sql-server/failover-clusters/windows/always-on-failover-cluster-instances-sql-server?view=sql-server-ver15&WT.mc_id=DP-MVP-5002576#FCIelements

Now you can start installing SQL Servers; on Node 1, you’ll set up the foundation for a SQL Server Failover Cluster (Installation of a Failover-Cluster), while on Node 2, you’ll only add a node to an existing SQL Server Cluster.

Depending on how this cluster is set up – whether it’s only one instance or many – SQL Server licenses must be acquired. You can choose between two operating modes: active/passive or active/active. When using active/passive, SQL Server instances can only run on one cluster node, but they can run on both nodes for a limited time in the event of a failure. When using active/active, all nodes can be used equally and for an unlimited amount of time, which is especially useful when dealing with several instances because it allows some kind of load-balancing.

If a node in the cluster breaks, the second node can no longer communicate with the other side and tries to get the broken services into his side as quickly as possible and start them there.

Unfortunately, a hybrid scenario is not possible due to the lack of scalable resources on-premise and in the cloud. However, a Failover-Cluster can be built in the Azure Cloud as an alternative. To do so, you’ll need a Proximity Placement Group, Managed Disks with the “Shared Storage” feature enabled, and the two virtual machines described above, whose installation and operation are essentially identical.

High Availability - Azure SQL Server Failover Cluster - DBCC2021

More on SQL Server high availability will be covered in a next blog post.

Aha effect when setting SQL instance parameters with dbatools

In the last week, I installed several SQL Servers for one customer and had to install and configure them all identically. What is closer here than to do this with a Powershell script, so I made the “effort” and the individual steps of the SQL Server configuration with dbatools to realize. I do not want to go into all the steps of the configuration in this post, but show only a part of it, which brought me a specific “aha effect”.

As part of the SQL Server configuration, the default values of “MaxDop” and “Cost Threshold for Parallelism” should be adjusted. Setting MaxDoP using Powershell or dbatools is relatively easy as there is a separate command for this, but for the “Cost Threshold for Parallelism” dbatools has a “work-around”. Unfortunately, there is not (yet) direct command for this.

Set-DbaMaxDop -SqlInstance sql2008, sql2012

This command-line sets the value of Max DOP (Maximum Degree of Parallelism) to the recommended value for SQL Server instances SQL2008 and SQL2012. Always in connection with this configuration parameter is the “Cost Threshold”, which still set to 5 by default.

All SQL Server instances at once …

To configure all SQL Server instances relatively quickly and easily, I have the command “Get-DbaRegisteredServer” (as an alias of Get-DbaRegServer) made. As preparation for this, I have created the necessary servers (here 2 servers with 3 instances each) as “Registered Server” on all servers in the SQL Server Management Studio and was then able to access it with Powershell aka dbatools.

According to dbatools documentation, this command retrieves a list of SQL Server objects stored in locally registered groups in both the Azure Data Studio and the central management server.

originell from dbatools.io - Many thanks to Chrissy

With this command and the possibility to pass the objects from the result object as a pipeline, you can do beautiful things like configuring the value for “MaxDoP” on all servers or instances in a command-line…

Get-DbaRegisteredServer | Set-DbaMaxDop

However, now to my aha effect with another command line 😉

Cost Threshold For Parallelism

As indicated above, the adjustment is only a work-around with dbatools and not with a dbatools command, this I use now “Set-DbaSpConfigure”. Of course, I could also configure the “MaxDoP” with this command, but then I have to provide for the previous determination and calculation of the respective value for MaxDoP, so determine the existing cores, these match the Best Practice and the value of one Pass variable to the set command. I set these values to 40 in 98% of all instances (unless the customer or the application wants something else), so I do not need any logic here.

Following my above logic or the documentation, I tried it with the following command line:

Get-DbaRegisteredServer | Set-DbaSpConfigure -Name 'CostThresholdForParallelism' -Value 40

This command brought me to an (at first sight) incomprehensible error (even my attempt to pass the value as a string was not successful):

WARNING: [13:02:23][Set-DbaSpConfigure] Value out of range for Server1\Instanz1 ( <-> )
WARNING: [13:02:23][Set-DbaSpConfigure] Value out of range for Server2\Instanz1 ( <-> )
WARNING: [13:02:23][Set-DbaSpConfigure] Value out of range for Server1\Instanz2 ( <-> )
WARNING: [13:02:23][Set-DbaSpConfigure] Value out of range for Server2\Instanz2 ( <-> )
WARNING: [13:02:23][Set-DbaSpConfigure] Value out of range for Server1\Instanz3 ( <-> )
WARNING: [13:02:23][Set-DbaSpConfigure] Value out of range for Server2\Instanz3 ( <-> )

Unfortunately, I have not found the reason for this, and maybe someone else can bring me closer to the phenomenon… maybe this is by design or even a “bug”…

However, I’ve been so successful with pipelining before that I’ve used that too… so let’s first find out all the SQL instances, then find the current parameter for the “Cost Threshold For Parallelism” on those instances, and then set it to the new value 40.

Get-DbaRegisteredServer | Get-DbaSpConfigure -Name 'CostThresholdForParallelism' | Set-DbaSpConfigure -Value 40
ComputerName  : Server1
InstanceName  : Instanz1
SqlInstance   : Server1\Instanz1
ConfigName    : CostThresholdForParallelism
PreviousValue : 5
NewValue      : 40

ComputerName  : Server2
InstanceName  : Instanz1
SqlInstance   : Server2\Instanz1
ConfigName    : CostThresholdForParallelism
PreviousValue : 5
NewValue      : 40

ComputerName  : Server1
InstanceName  : Instanz2
SqlInstance   : Server1\Instanz2
ConfigName    : CostThresholdForParallelism
PreviousValue : 5
NewValue      : 40

ComputerName  : Server2
InstanceName  : Instanz2
SqlInstance   : Server2\Instanz2
ConfigName    : CostThresholdForParallelism
PreviousValue : 5
NewValue      : 40

ComputerName  : Server1
InstanceName  : Instanz3
SqlInstance   : Server1\Instanz3
ConfigName    : CostThresholdForParallelism
PreviousValue : 5
NewValue      : 40

ComputerName  : Server2
InstanceName  : Instanz3
SqlInstance   : Server2\Instanz3
ConfigName    : CostThresholdForParallelism
PreviousValue : 5
NewValue      : 40

Also, already I have found out something great for myself and am more enriched by experience in dealing with dbatools!

I love this Powershell module, which allows me to customize, optimize, and automate many (almost anything!) Things around and around SQL Server. I like to use it (as you can see my other blog posts) and meanwhile with all my clients. THANKS to @Chrissy and the many other contributors who are taking the trouble to make this community tool!

Photo by Ben White on Unsplash

#4 SQL Server Configuration – implement Best Practices

I hadn’t been writing this Powershell series for a long time, and I’d like to make up for it, even though a lot of things have changed (in my work & community life) … I’d like to introduce you to two things today, once in a conventional way and how Powershell could configure SQL Server (or how I did it in my script), and a simpler and faster way with the Powershell module from dbatools.io.

Best Practices with T-SQ

As part of the SQL Server installation, you should optimize certain parameters to guarantee high-performance and stable operation. This includes a variety of configuration parameters at the instance level, such as “Max. Memory” or “Max. degree of Parallelism”. All these instance settings can be set with the same SQL Server function, so I have written a “function” for these recurring T-SQL commands to stay flexible for later extensions.

function ExecuteSQLCmd ([string]$SQLQuery) {
     Invoke-Sqlcmd -ServerInstance $ServerName -Query $SQLQuery -QueryTimeout 65535
}

With this simple function (even before, but now it is “easier”), I can call the following functions accordingly and configure my SQL Server according to Best Practices, in which I call the respective function, calculate values according to system equipment then execute it with ExecuteSQLCmd. The following function enables me to adapt it to the respective environment.

SetMaxMemory
Add_TempDBFiles
SetMaxDOP
SetNetworkPacketSize
SetOptimizeAdhocWorkload
SetBackupCompression
AddLocalSystemToSysadminGroup
enable_XPAgent

Example – Powershell Function “SetMaxDOP”

In order to set the value for MaxDOP (max degree of parallelism), I have to know how many logical CPUs the server has. I determined this value I had at the beginning of the script through auxiliary functions, only with this value I can decide… Usually, I set the Cost Threshold for Parallelism on our systems to 40, this fits at least 90% of the systems. Of course, you can still have a lot more to stick to the best practices, as you can read in the next section, but with these values, I was going quite well on our systems for the last two years.

function SetMaxDOP() {
    Try { 
        Write-Host "Setting of MaxDOP / Threshold"
        $sqlquery = "
        EXEC sys.sp_configure N'show advanced options', N'1' RECONFIGURE WITH OVERRIDE;
        EXEC sys.sp_configure N'cost threshold for parallelism', N'40';
        "
        ExecuteSQLCmd $sqlquery

        if ($global:NoLogicalCPUs -le 4) {
            $sqlquery = "
            EXEC sys.sp_configure N'max degree of parallelism', N'0'
            RECONFIGURE WITH OVERRIDE
            "
            Write-Host "[INFO] Set Threshold to 40 and Set MaxDOP to 0."  -ForegroundColor Green
        } else {
            $sqlquery = "
            EXEC sys.sp_configure N'max degree of parallelism', N'"+($global:NoLogicalCPUs/2)+"'
            RECONFIGURE WITH OVERRIDE
            "
            Write-Host "[INFO] Set Threshold to 40 and Set MaxDOP to "($global:NoLogicalCPUs/2) -ForegroundColor Green
        }
        ExecuteSQLCmd $sqlquery
    }
    Catch {
        Write-Host "[ERROR] Failed to set MaxDOP." -ForegroundColor Red
    }
}

dbatools – the function Set-DbaMaxDop

I had already written several times about the Powershell module dbatools – for example when copying an agent job – here I would like to introduce you now the comparison between the conventional way and the easier way with dbatools. Dbatools provides a function for simply setting the SQL Server instance parameter for Max Degree of Parallelism, as well as other instance parameters.

The “Set-DbaMaxDop” command offers a variety of options, the simple setting of the MaxDop at the instance level (SQL Server 2008 – 2016) and the setting of the MaxDop at the database level starting with the SQL Server 2016. The function determines all the basic conditions, based on the algorithm from the KB2806535, as well as the MaxDoP Calculator from Sakthivel Chidambaram, are used to calculate the necessary values for setting the MaxDoP. Where, of course, – as with my data/notes – it must always be pointed out that these are recommendations that do not fit 100% to every environment and application, but give the first clue.

Set-DbaMaxDop -SqlServer SQL2016

dbatools - Set-DbaMaxDop - Set to Best Practices

If you want to specify a value yourself, this is also possible … or use the internal test function “Test-DbaMaxDop” Test-DbaMaxDop -SqlServer SQL2016

dbatools - Test-DbaMaxDop

Or even decide for yourself what value is more appropriate for this environment …Set-DbaMaxDop -SqlServer SQL2016 -MaxDop 6

dbatools - Set-DbaMaxDop - Set to your own Value

Further information can be found on the following pages dbatools.io: https://dbatools.io/functions/set-dbamaxdop/ and https://dbatools.io/functions/test-dbamaxdop/

dbatools – the function Set-DbaSpConfigure

Now we have changed not only the value for MaxDop but also the value for the Threshold for the Max Degree of Parallelism. Also, this value can be set with the dbatools very easy. Since both are instance parameters, you can customize both settings individually with your own values and this command, but the internal calculation makes the use of two different commands useful. So to set the value for the threshold to 40, I use “Set-DbaSpConfigure”, which should not be unknown to us.

Set-DbaSpConfigure -SqlServer SQL2016 -ConfigName CostThresholdForParallelism -Value 40

dbatools - Set-DbaSpConfigure

Especially with the IntelliSense feature, this function is a joy since the individually available parameters can be used quickly and you can quickly get the whole command. You will also find further help and examples on the help pages of the function => https://dbatools.io/functions/set-dbaspconfigure/

Thus, as opposed to my own script, you can now optimize both instance parameters with only 3 lines of code.

Import-Module .\dbatools\dbatools.psd1

Set-DbaSpConfigure -SqlServer SQL2016 -ConfigName CostThresholdForParallelism -Value 40
Set-DbaMaxDop -SqlServer SQL2016