Recently I reviewed filtered indexes, this time let’s look at columnstore indexes. These indexes are very useful for data warehouse workloads and large tables. They can improve query performance by a factor of 10 in some cases, so knowing and understanding how they work is important if you work in an environment with larger scaled data. Now, I admit when these first were introduced in SQL Server 2012 I found them very intimidating (additionally, you couldn’t update them directly). For me, anytime you say columnstore, my mind tends to set off alarms saying wait stay away, this is too complicated. So, in this post I am going to try and…
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When you run a query twice, and get dramatically different run times, your first step can be to try to identify the differences in execution plans. For many that means running the two different queries (before & after) and splitting you screen in order to visually compare the plans. Did you know SQL Server Management Studio gives you the option to compare to different execution plans? It makes it easy not only to visualize the differences, but it also shows you detail properties that allow you to dive into the numbers. This functionality was introduced with SQL Server 2016, and is also part of the functionality of the Query Store…
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In this post, we continue with another beginner’s blog of database features that may be unknown to many. Let’s take a look at filtered indexes. Many database administrators are fully aware of the power of indexes and know how to create them. However, I find that some have yet to dive into fully optimizing their indexes and taking advantage of what filtered indexes has to offer. What is a filtered index? Simply it’s an index with a where clause. It is an optimized non clustered index that can be narrowed down in scope to better fit a subset of data. Example being date ranges, years, non NULLs or specific product…
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I give performance presentations at many different events to all levels of SQL Server professionals. Over time I’ve noticed that some DBAs and developers have never looked at the dynamic management views (dmv’s) that are available within SQL Server starting with SQL Server 2005. These DMVs are useful means to determine what is going on with a particular SQL Server instance. So, in this post I am going to list a few of my very favorite DMVs as a reference for those who may be new to them. Performance Tuning These dynamic management views are what I use first when looking to any performance issues or I need to know…
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I am very excited to announce I will be delivering a pre-conference session on SQL Server Performance Tuning on November 5th at PASS Summit 2019. If you have ever attended one of my sessions, you know how passionate I am about this particular topic. So, you also know how very excited I am to have this opportunity to spend a full day talking about SQL Server Performance Tuning and Optimization. Performance Tuning is one of my favorite things to do with SQL Server. There is nothing like seeing performance improvements in an environment as your reward for your hard work. It’s tangible and gratifying. In this session you will be…
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Another quick post of simple changes you can make to your code to create more optimal execution plans. This one is on implicit conversions. An implicit conversion is when SQL Server must automatically convert a data type from one type to another when comparing values, moving data or combining values with other values. When these values are converted, during the query process, it adds additional overhead and impacts performance. Here is a great chart by Microsoft that shows you conversions and which will cause an implicit or explicit conversion. In this post I will not go into explicit, just know that is what you explicitly tell SQL Server to CAST…
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One of the easiest things to fix when performance tuning queries are Key Lookups or RID Lookups. The key lookup operator occurs when the query optimizer performs an index seek against a specific table and that index does not have all of the columns needed to fulfill the result set. SQL Server is forced to go back to the clustered index using the Primary Key and retrieve the remaining columns it needs to satisfy the request. A RID lookup is the same operation but is performed on a table with no clustered index, otherwise known as a heap. It uses a row id instead of a primary key to do…
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March is Women’s History Month, to celebrate the PASS Women in Technology Virtual Group (@PASS_WIT) held a webcast featuring prominent woman in the Data Platform community. I had the pleasure of being one of five panelists alongside these amazing women Lori Edwards (B|T), Malathi Mahadevan (B|T), Kellyn Pot’Vin-Gorman (B|T), and Catherine Wilhemsen (B|T). Discussion ranged from direct technical topics to what it’s like being a woman in tech. Women took turns providing advice around having a degree and/or certification to succeed in tech. We discussed how to keep up with advances in the field and skills that technologists should have. Specific to being a woman in tech, we talked about…
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I’ve seen many people go through the trouble of setting up database mail and configuring SQL Agent Alerts only to realize it’s not working. The reason in the cases I’ve seen is because they have simply neglected to assign a mail profile to SQL Agent. This is way more common than you would think, thus I wrote this quick blog. This check box and drop down can sometimes lead to hours of troubleshooting if you don’t know where to look. In order to receive the alerts, you must enable a mail profile. This would be the profile created during the Database Mail configuration process. To configure SQL Server Agent to…
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Recently I had a client complain of chronic high CPU utilization. The performance of their SQL Server had degraded, and it appeared to be related to higher than normal CPU utilization in conjunction with symptoms of unresponsive user queries. The root cause was twofold—a third party hosting provider had overallocated virtual processors on the physical host where the virtual machine (VM) running SQL Server was residing, as well as a recent upgrade from a version of VMWare that was not patched for Spectre and Meltdown. The host had 16 physical cores and was hyperthreading (making it effectively 32 cores) until the hosting provider patched from VMWare 5.5 to a newer…
