What causes SQL Server to have performance issues or run slow?

Today’s post is a guest article written by a friend of the blog, Kevin Kline, an expert on SQL and Microsoft SQL Server.

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SQL Server can suffer from all sorts of problems if it is not properly optimized, and thankfully with the help of performance tuning, you can overcome common complications.

Of course, the first step to fixing flaws in SQL Server is understanding what causes them, so here is a look at the common symptoms to look out for and what they may indicate.

Hardware hold-ups

One of the first things to consider when addressing server performance imperfections is that the hardware itself may not be adequate to accommodate the kinds of uses you have in mind.

For example, if your storage is reaching its capacity or your CPU is being pushed to its limits in the handling of the queries that are being fired at the server throughout the day, then the only option may be to upgrade the overburdened components.

Of course, there are ways to make better use of the hardware resources you have available without splashing out on expensive new equipment. This can include increasing the maximum amount of memory that SQL Server can use, which is a widely used quick fix that is worth trying out, especially if you have previously stuck to the default settings without doing any tinkering.

A simple, cost-effective upgrade that can be considered is to migrate data from traditional hard disks to solid state storage, the price of which has fallen significantly in recent years.

Networking imperfections

If you have checked your server’s hardware resources and seen that they are not being taxed, then sluggish performance could instead be down to the network itself.

Analyzing traffic and testing connectivity will allow you to work out whether your SQL database is being hamstrung by the infrastructure which it relies upon to serve end-users.

Software snafus

Before delving any deeper into troubleshooting SQL Server performance, it is worth checking on the software side of the equation to make sure that no errant processes are monopolizing hardware resources unnecessarily.

It is perfectly possible for the OS to throw up unexpected issues of this nature from time to time, and often these can be fixed by simply killing the process in question, so long as it is not a lynchpin of the entire software environment, of course.

Index issues

Well-maintained indexes are key to keeping an SQL database running smoothly, which is why you should aim to look out for index fragmentation if you are experiencing problems, or even if you are not.

Make sure to schedule this on a consistent basis so that you are not left with seriously fragmented indexes that are entirely sub-optimal. Your maintenance schedule should be set according to your own needs, which is why you also need to stay on top of server monitoring so that you can make informed decisions.

Query qualms

If particular queries are used very frequently and tend to take up a lot of your I/O throughput and server CPU grunt, it is likely that there is room for improvement here.

There are lots of ways to optimize SQL queries, and it makes sense to focus your attention on the most commonplace queries, since even if you only make a minor enhancement you should see big performance gains.

It is best to see SQL Server maintenance as an ongoing process, rather than one which can be carried out once and then considered as complete. Being attuned to the likely issues that might arise will let you act swiftly when they do emerge, and even let you preemptively prevent them so that performance is always top-notch.

Written by Kevin Kline
Kevin serves as Principal Program Manager at SentryOne. He is a founder and former president of PASS and the author of popular IT books like SQL in a Nutshell. Kevin is a renowned database expert, software industry veteran, Microsoft SQL Server MVP, and long-time blogger at SentryOne. As a noted leader in the SQL Server community, Kevin blogs about Microsoft Data Platform features and best practices, SQL Server trends, and professional development for data professionals.

About craig@craigsmullins.com

I'm a data management strategist, researcher, and consultant with over three decades of experience in all facets of database systems development and implementation.
This entry was posted in DBA, Microsoft SQL Server, optimization, performance, SQL. Bookmark the permalink.

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