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…
-
-
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…
-
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…
-
We all have the need to collect system and performance information regarding our SQL Servers. Some of us use third-party tools, SQL Trace, or a homegrown solution. Did you know Microsoft has a built-in tool to help you accomplish this? It’s called Data Collection and the data it collects (collection sets) is stored in a relational Management Data Warehouse. The data collected is used to generate reports giving us in with very readable and useful insights to our servers. Not only can you get performance information, but you can also use SQL Profiler to export trace definition and create custom collection sets. This is not a new SQL Server feature,…
