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Category: Administration

Troubles with Dropping Logins

Published 2019-09-27 by Kevin Feasel

Pamela Mooney takes us through a scenario involving dropping a user and login, and some of the difficulties which might arise:

I had to obscure a lot, but the bottom query results correlate to the top results.  The first line of the bottom query results show the grantor of the permissions, and the bottom line is the grantee.  In this case, a login was explicitly denied impersonation on a server role.  I’m using this example because it is really quirky to fix.  Most often, you’ll just reverse the permissions, using pretty standard syntax. Even easier, right click on the login, go to the “Securables” tab, and remove the permissions.  However, if you are a fan of the TSQL approach, this one is not so straightforward, so it’s a good one to show.  

Click through for a demonstration.

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Instant Transaction Rollback in SQL Server 2019

Published 2019-09-26 by Kevin Feasel

Matthew McGiffen explains that Accelerated Database Recovery in SQL Server 2019 works for more than just startup times:

If you’ve read about the Accelerated Database Recovery feature in SQL Server 2019 you could be forgiven for thinking it’s just about speeding up database recovery time in case of a server failure.

In fact, enabling it also means that where you have a long running transaction that fails or is cancelled the rollback is almost instantaneous. This is great news for DBAs who have to sometimes kill a long-running blocking transaction but worry that it may take a long time to rollback – continuing to block all that time.

Read on for an example. I hadn’t thought about this, but it’s pretty cool.

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Power BI Admin API Updates

Published 2019-09-25 by Kevin Feasel

Matthew Roche takes us through a few updates to the Power BI Admin API:

Even with these new experiences, there will still be times when you want or need to use the Power BI API to get insight into all the workspaces in the Power BI tenant for which you are an administrator. This ability isn’t new, but some recent updates to the Power BI admin API have made it easier.

I don’t do a lot of development these days, so when a post titled Avoiding workspace loops by expanding navigation properties in the GetGroupsAsAdmin API showed up on the Power BI blog, I didn’t pay much attention. I should have.

Read on for the full set of updates.

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Ring Buffer CPU Over 100%

Published 2019-09-24 by Kevin Feasel

Thomas Rushton ran into an oddity with sys.dm_os_ring_buffers:

Wait! Process Utilization + Idle adds up to waaaaay over 100…What’s going on?

My first thought was that the CPU was being throttled, so I checked the windows power options – for some really irritating reason, Windows defaults to a “balanced” power setting, which is rubbish for SQL Server.

That looks OK, but… if you check the CPU page of the Task Manager, things are a bit more interesting:

Unfortunately, the story doesn’t have a conclusion, but Thomas’s conjecture does make sense.

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Azure Kubernetes Service Max Volume Count

Published 2019-09-23 by Kevin Feasel

Chris Taylor explains an error message in Azure Kubernetes Service:

Whilst playing around with my session for Techorama.nl I encountered an error I hadn’t seen previously whilst deploying SQL Server on Linux in Azure Kubernetes Service (AKS)

0/1 nodes are available: 1 node(s) exceed max volume count

The yaml I used was only slightly modified (mainly names) from scripts used on minikube and docker-desktop so I was a little confused as to why I was getting this in AKS.

Read on to understand what’s happening here and how you can fix it.

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Read-Only versus Read-Write and SQL Server

Published 2019-09-23 by Kevin Feasel

Jack Vamvas takes us through what it takes to turn a read-write database in SQL Server read-only and vice versa:

There are some considerations for deciding if a Developer should be able to include as part of an ETL process , the capacity to change the READ STATE of a SQL database

1) Requires ALTER permission on the database. This is an elevated privilege – and may break the organisations sql server security policy

2) Is the developer on the hook for maintaining Production data? What is the developer’s role in supporting production data ?

Read on for the commands as well as additional considerations before you grant these permissions.

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Version Store and ONLINE Operations

Published 2019-09-20 by Kevin Feasel

Josh Darnell takes us through how SQL Server manages ONLINE = ON operations (such as index building and rebuilding) using the version store:

The votes table has about 10 million rows in it, so this takes a bit of time (10-15 seconds if nothing else is happening). If I check sys.dm_tran_version_store_space_usage and sp_WhoIsActive, I can see that:

– the version store is not growing, and
– the ALTER statement is chugging along making progress

There are costs to setting ONLINE = ON. I think they’re almost always worth it, but it’s important to remember that they are there.

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Starting SQL Server in Single-User Mode

Published 2019-09-20 by Kevin Feasel

Ranga Babu has a few methods for starting SQL Server in single-user mode:

It is advisable to use SQLCMD when you want to query SQL Server that is started in single user mode as connecting directly and query using SQL Server Management Studio that uses more than one connection. To query SQL Server single user mode using SQL Server Management Studio, open SQL Server Management Studio, and do not connect to SQL Server directly. Close the connection window and click on New Query as shown in the below image which opens a query editor in SQL Server Management Studio:

I recommend practicing this a few times, as the only time you’d actually start SQL Server in single-user mode is during an emergency and that means people breathing down your neck (figuratively if not literally).

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Reading SQL Server Logs from Kubernetes

Published 2019-09-16 by Kevin Feasel

Anthony Nocentino shows us how we can use kubectl logs to read the SQL Server Error Log:

We can use follow flag and that will continuously write the error log to your console, similar to using tail with the -f option. If you remove the follow flag it will write the current log to your console. This can be useful in debugging failed startups or in the case below, monitoring the status of a database restore. When finished you can use CTRL+C to break out and return back to your prompt.

Read on for a brief demonstration.

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Hot Patching Azure SQL Database

Published 2019-09-13 by Kevin Feasel

Hans Olav Norheim has an interesting paper on a technique Microsoft uses to release SQL Server patches for Azure SQL Database while minimizing downtime:

The SQL Engine we are running in Azure SQL Database is the very latest version of the same engine customers run on their own servers, except we manage and update it. To update SQL Server or the underlying infrastructure (i.e. Service Fabric or the operating system), we must stop the SQL Server process. If that process hosts the primary database replica, we move the replica to another machine (requiring a failover).
 
During failover, the database may be offline for a second and still meet our 99.995% SLA. However,  failover of the primary replica impacts workload because it aborts in-flight queries and transactions. We built features such as resumable index (re)build and accelerated database recovery to address these situations, but not all running operations are automatically resumable. It may be expensive to restart complex queries or transactions that were aborted due to an upgrade. So even though failovers are quick, we want to avoid them.

Read on to see how they do it. There’s no on-prem analogue yet, though perhaps that will come in time.

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