The Best Ways to Improve SQL Query Performance

The foundation of any relational database is made up of the SQL queries you compose. With them, you can extract data and deliver it to end-users on the fly.

Of course, not all queries are created equal, and it is possible to improve how they perform through tweaks and techniques. Here are just a few best practices for boosting the performance of SQL queries.

How to monitor SQL Server performance

Before you can get into the nitty-gritty of improving query performance, you need to have an overview of how well optimized your database is as a whole.

There are plenty of different monitoring solutions available, including those that feature an SQL server query plan tool that empowers you when it comes to catalyzing queries in particular.

All sorts of factors can influence server performance, and different issues may be behind flaws and inefficiencies. Checking things like wait statistics, as well as looking for blocking and deadlocking, will stand you in good stead.

The reason to use third-party monitoring solutions is that they can automate common administrative tasks. So rather than having to manually root out imperfect queries, you can let the software do this for you, with customizable alerts taking the convenience even further.

Optimizing your indexes

One of the simplest ways to improve SQL query performance is to make sure that your indexes are properly optimized. This means defragmenting them on a regular basis so that they do not become disordered and can retrieve the right information efficiently.

Index fragmentation is part and parcel of how SQL databases operate, so it is not something you can prevent entirely. However, there are some things to think about which might change the way you use indexes in the first place.

For example, in the case that a table contains a relatively small amount of data, an index may be superfluous and could actually hurt performance rather than improve it.

Another aspect of index optimization which is relevant from a performance perspective is the fact that when rebuilding indexes, you need to be aware of how you schedule this process.

Planning for it to occur when the database is likely to undergo significant usage is clearly not sensible, so instead plot out your index maintenance tasks to take place during off-peak times.

There are a host of other strategies to take onboard when working on your indexing, but getting the top-level basics of optimization and maintenance down pat will work in your favor in the long run.

Monitoring the SQL Server TempDB

TempDB is a lot like indexing in that it is one of the cornerstones of the way SQL Server functions, and without it you could face all sorts of complications in terms of data integrity and reliability.

However, TempDB is far from immune when it comes to causing SQL query performance snafus. In short, it is the place where transient data is stored, and so it is used by any processes that are active across entire server instances.

As the name suggests, TempDB is only supposed to store information temporarily, before discarding it when it is no longer needed by a process, business app, or user.

Furthermore, even if you have more than one server instance running, all of these will share the same TempDB allocation, which means that it is a major point of vulnerability in terms of performance.

One of the main things to look out for when monitoring TempDB is the amount of storage space it is using.

If it fills up because transactions have not been completed properly or temporarily stored data has not been removed, then a whole SQL ecosystem can come screeching to a halt.

Using monitoring tools will of course give you insights into the ebb and flow of TempDB over time, and you can use these to pinpoint problems and snuff them out as soon as possible.

Monitoring system resources

In addition to keeping your eye on how aspects of the database software are operating from moment to moment, it is also wise to look into the way that the server’s hardware resources are being used.

This can further narrow down potential pain points when you are troubleshooting sluggish query performance.

For example, if certain processes are hogging CPU threads, memory, network bandwidth, or I/O availability, then this could indicate a wider issue that needs addressing.

Sometimes this can be fixed quickly by simply terminating the problematic process, or rebooting the server if necessary.

Occasionally a more comprehensive fix is required, and this will very much depend on the specifics of the fault itself.

Another conclusion that you could draw from monitoring system resources is that the queries themselves are not poorly optimized and processes are not misbehaving; instead, it might be that your server hardware is no longer fit for purpose.

Monitoring system resources is therefore not just about seeing if there is room for optimization today, but also about planning ahead. As your database grows and the hardware is pushed further, you can estimate when upgrades will be necessary and stay ahead of the curve.

Query tuning

Last but by no means least, look at queries to see if tuning will deliver performance boosts. You can find suboptimal queries using some of the monitoring techniques and tools mentioned above and then iron out imperfections based on your findings.

Ideally, you will be familiar enough with SQL to spot poorly constructed queries, but there are some simple strategies to consider. For example, be specific with the fields you use in conjunction with the SELECT statement, rather than having the query scour the entire table to find what you need. A longer query will be quicker than a shorter one.


Database administrators always need to be vigilant for SQL query performance that is not up to standard, and sticking to best practices is better than taking shortcuts.

By doing things right the first time, you will save yourself a lot of hassle and extra work further down the line, so it is better for all involved.

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