Dedicated Admin Connection is one of the easy-to-forget features in SQL Server that can really save your day. DAC (no relation to Data-Tier Applications, just shares the acronym), as it’s often called, is the way you can try to access a SQL Server instance that is in such a bad shape, that no normal connection is available. This can be due to resource exhaustion or if you happened to create a slightly wonky logon trigger. In this post we’ll look at how you enable Dedicated Admin Connection (for remote users) and how you connect to SQL Server using the DAC.
I recently had a discussion about the ability to offload DBCC CHECKDBs to a secondary database using Active Secondaries in SQL Server Availability Groups. While it is fully possible to run database consistency checks against secondary database (and there’s plenty of recommendations floating around for doing this), it needs to be pointed out that using Availability Groups for this does not equal of running checks on the primary database.
Let’s consider this for a bit…
In my previous post about logical joins I wrote about the most common type of SQL Server join, the INNER JOIN. Naturally the logical follow-up is to look at the OUTER JOIN. Syntax for OUTER JOIN is bit different from the INNER JOIN, as you need to define either LEFT, RIGHT or FULL keyword (more about FULL in another post). Unlike the INNER JOIN which only returns rows from the tables if there are equal values in join column, OUTER JOIN will return all the rows from either LEFT or RIGHT even if there is no matching value in the table you are joining.
While back I wrote this blog post about SQL Server joins, the focus back then being in the physical ones. So I figured that now would be a good time to re-visit the topic and look at the logical joins also. Where the physical joins are decided by the SQL Server engine the logical joins are the ones we write. There are quite a few different kind of logical joins, so I will be writing multiple posts about this topic.
I was recently looking at some Execution Plans with a co-worker and we ended up discussing the different types of joins in a SQL Server and what implications they might have when it comes to query performance. While many of us are familiar with writing joins, as we usually don’t query just a single table, there are quite few things about the physical joins that may not quite obvious. In this post our focus will be in the physical joins, but we will also very briefly look at the different types of logical joins also.
It was not long ago that I though DevOps to be one of those things that happened to other people, and honestly, I did not give it that much thought. That was a time when I was a DBA in the part of the company that does deployments and support for our products, the Ops.
After working in the Ops for almost 20 years, at the beginning of the 2017, I transferred from the Ops to the Dev to lead a small team of database developers on a grand quest to save the world. For me this has been an eye-opening experience in many ways and it has also made me realize the value and possibilities of the DevOps culture.
Let me tell you a story on what happened and brought on this change of heart.
SQL Server has had the Data Compression feature for a while, ever since the version 2008, so it is hardly a new thing. However as it has been Enterprise Edition feature until SQL Server 2016 Service Pack 1, it is not something you see employed very often. Technically speaking, you could also compress data before 2008 by using NTFS file level compression on a read only data. However with the implementation of SQL Server Data Compression you could now do it inside the database on a page or a row level.