Using The DAC

Andrea Allred shows us how to use the DAC:

The DAC, what is it? It is the Dedicated Administrator Console. Basically it is a way to connect to your SQL Server when all the other connections are tied up. But it takes a little bit of pre-planning so that you can use it when things go bad with your SQL Server.  Let’s enable it so you can test using it and know that it is there in the future.

This is your “get out of jail free” card when the instance is completely unresponsive.  A small amount of memory is dedicated to the DAC so that even if anything else is locked up, you have a chance to fix the problem short of a reboot.

Generating Test Data

Erik Darling points to a simple site designed to generate test data:

A website I really like to help generate data is over here. It’s really easy to set up data the way you want, and you get a lot of neat customization options for a wide variety of data types.

There are also tools (both free and paid) which help generate SQL data, but this site includes other output formats as well.

Setting Up Azure SQL Database With Powershell

Mike Fal creates and does basic configuration of an Azure SQL Database instance using Powershell:

From a logical standpoint, working with Azure SQL databases is not very different from setting up a SQL Server instance and database in your environment. There are 3 main components we will need to deploy:

  • A server

  • A database

  • A firewall (server or database)

This is the second part in his series.

NUMA With Few Cores

Denny Cherry asks and answers the question of how many NUMA nodes we should use on a server with a large amount of RAM but relatively few cores:

For this example, let’s assume that we have a physical server with 512 Gigs of RAM and two physical NUMA nodes (and two CPU sockets). We have a VM running in that machine which has a low CPU requirement, but a large working set. Because of this we have 4 cores and 360 Gigs of RAM presented to the VM.

The answer is not trivial, making this an interesting question.

Database In Recovery

James Anderson had a database which would drop into In Recovery mode a few times throughout the day:

The database in question wasn’t stuck in recovery, it would slip in and out of the status throughout the day. Normally, I would only ever expect to see a database in recovery during a restore or after a service restart. Once recovery is complete, I would not expect to see the database slip into ‘in recovery’ again. I especially wouldn’t expect a database to keep slipping in and out of recovery.

The answer is a true head-slapper.  Whose head, I’ll leave up to you…

Optimizing OR Clauses

Daniel Hutmacher looks at different ways of optimizing queries with multiple conditionals and different parameters:

The SQL Server query optimizer can find interesting ways to tackle seemingly simple operations that can be hard to optimize. Consider the following query on a table with two indexes, one on (a), the other on (b):

FROM #data
WHERE a<=10 OR b<=10000;

The basic problem is that we would really want to use both indexes in a single query.

We get to see a few different versions of the query as well as the execution plans which result.

Using The OUTPUT Clause

Steve Jones shows how to use the OUTPUT clause with an INSERT statement:

I got asked a question about the OUTPUT clause recently and realized I didn’t remember the syntax. I’ve rarely used this, so I had to look it up and thought this would be a good basic post.

The idea with OUTPUT is that the data from the inserted and deleted tables can be output from the INSERT statement, outside of your triggers. This is the same data, but you can access it in the insert.

The format is

INSERT xxx OUTPUT yyyy INTO @zzz VALUES (or SELECT) mmmm

If I had one thing I could change about OUTPUT, I’d like to be able to output directly into variables for those cases in which I know I’m only going to get one result (or maybe I only care about one arbitrary result in a set).

Graphing CPU Utilization

Slava Murygin uses spatial data types to graph CPU utilization on a SQL Server instance:

That diagram provides you about 260 last minutes of Server CPU usage and measured in percents.

As you can see my SQL Server is mostly doing nothing and only during that blog-post writing in the last half and hour or so it is heavily running test scripts to over-utilize my CPU, but it still barely goes more than 60% of CPU (Blue line).

The Red line represents all other processes besides of SQL Server and you can tell if anything else from outside is impacting your performance.

Combined with Glenn Berry’s diagnostic queries, you could generate some quick analytics.  I’d still use R for anything more than slightly complicated, but this is great for those environments in which you don’t have good alternative tooling.

Introduction To Service Broker

Colleen Morrow is starting a series on Service Broker:

So why am I such a big fan of Service Broker and if it’s so great, why isn’t everybody using it? Let me start by telling you why I’m such a fan.

  • Asynchronous – The biggest benefit of Service Broker, or probably any messaging technology, is that is decouples long running processing from the client application.  A great example of what I mean by this is  When you place an order at Amazon, a whole series of backend processes are initiated.  Your payment is processed, inventory is verified and updated, fulfillment and shipping is initiated, etc.  All of which ultimately end with a box arriving on your doorstep.  But the website doesn’t wait for all of that stuff to finish before it thanks you for your order.  Your order information is added to a queue and the page returns.  All that other stuff is handled asynchronously.  And that’s what Service Broker lets you do in your database.

I think the biggest impediment to adoption of Service Broker is that there was never a friendly UI.  The same applied to Extended Events in 2008.  Both involve a non-trivial amount of setup and maintenance, and the tooling just hasn’t been there for Service Broker.  I know they’re still making (minor) improvements to the product, but if they wanted a big improvement, putting a friendly UI tie-in with Management Studio would go a long way.

Maintaining Full-Text Indexes

Dave Mason talks about full-text index maintenance:

My first encounter with full text indexes and degraded performance was related to an enhancement I made to an aspx page years ago. I wanted all of the search fields to use an AutoComplete AJAX extender to mimic the behavior you see when you type a few letters into the search field on or A traditional non-clustered index wasn’t sufficient for the “Location Address” field, so I settled on a full text index–it worked very well.

After some amount of time (I don’t remember how long), performance slowed considerably. I was surprised to find the full text index for “Location Address” had a large number of fragments. I wish I had kept some notes on my findings. I can’t remember how may fragments there were, but I’m thinking it was in the 15-20 range. If memory serves me, Orange Co., FL has about 400,000 physical location addresses. The underlying table had one row per location address. Knowing me, the indexed column was probably VARCHAR(100) or VARCHAR(128). This does’t seem like a huge amount of data, so I was surprised the full text searches were slow, even with 15-20 fragments. Reorganizing the related full text catalog made a world of difference. Performance improved drastically.

All indexes need maintenance.  Dave has a script to help with full-text indexes.


September 2019
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