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Posted 4 Jul 2013


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The Basics of ASP.NET Performance Optimization

4 Jul 2013CPOL15 min read
Microsoft MVP Tiago Pascoal goes through the best practices, tools, and techniques he uses to optimize the performance of web applications.

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Performance is something that you should be thinking about during development, rather than just when you’re debugging, but it is often considered a “black art”, fueled by guesswork and necessity.

Developers often rely on their gut instincts, and focus on sections of code that they think are slow. The danger here is that you might end up with a 100x speed-up (great!) on a section of code that only contributes to 1% of the overall experience (not so great). Or even worse, your speculation might just be flat-out wrong, and there’s no problem where you looked.

This way of optimizing is painfully slow, boring, and quite frankly, expensive. At the risk of stating the obvious, if you want to avoid wasting time hunting for the real issues, then when the time comes to optimize, don't speculate. Measure where the time or memory is being spent using one of the many tools and profilers available, and focus your time and energy where a change will have the maximum impact on the overall performance of the system.

That’s a principle I’m going to come back to through this article – guesswork is pointless, and there are tools out there that let you zero right in on your problems, so use them! With that in mind, I’m going to describe some of the most fundamental techniques and tools you should use to ensure you’re maximizing the performance of your ASP.NET applications, so let’s get started…

Factors in Performant Applications

Writing code that isn’t a slouch is something within the reach of all developers and, with the right tools and some practice, it’ll become second nature to you. It really helps if you’re considering performance, not as an afterthought (when issues will be much costlier to resolve), but as part of day to day development.

Let’s quickly summarize a few reasons why you really should care about your application’s performance up-front:

  • If your users get a poor user-experience, become frustrated, and start complaining, then you have to spend days debugging instead of writing new code.
  • Cost! There are generally two ways to making an application faster: spending more money on hardware (this is even more true in the cloud-web world where a poorly tuned SQL query might lead you to buying a whole new database server unnecessarily), or fixing your code.
  • Once performance becomes a problem in production, it can involve architectural rework to fix, which is not only painful, but also pulls you away from new work.
  • It’s satisfying to see a job done well first time round, and to know that your users love using your application.

Let’s assume that, if you’re still reading, you probably appreciate the benefits of optimizing your ASP.NET application for improved performance. Broadly speaking, there are three areas which are going to affect your application’s performance:


Let’s face it; the vast majority of applications don’t need to be built with extreme speed in mind, they only need to be fast enough. Although that said, I’ve yet to find a user that doesn’t complain about speed, no matter how fast the application is. Humans are a curious bunch.

However, the key thing to remember is that the important point of view when you’re tracking down performance issues is the user’s point of view – always make sure you’re focusing your energy on problems which will affect the user, rather than bits of code which you think might be running slowly.

Compilation and Configuration

To get the best out of your application, compile the code correctly and configure the system with debug features disabled. Compiling the code in non-debug mode and with the highest level of optimization will make sure that the compiler generates more efficient code (this has other repercussions, but that’s a story for another day). On byte code systems like .NET, debug features will prevent the JIT compiler from emitting the most effective code, as the generated code will have extra information for debugging purposes and will not be fully optimized.

At the same time, make sure your application and target environment system are correctly configured to maximize performance. For example, a few things you should consider include: keep logging level at an appropriate level for a production system (so we don’t incur an unnecessary overhead), enable compression (even for dynamic content), and have a sensible caching strategy for static content.

The Code

The fastest code is the code that doesn’t run at all. However, since code that is not executed would not be very useful, when code is written it should be written with performance in mind, so let’s take a look at how we can get the most out of what we write.

Tools and Techniques

I am a firm believer in the maxim of Make it Work, Make it Right, Make it Fast (in that order), but even when you start working on “Fast”, it can be easy to start looking for the problem in the wrong place. Of course a good place to start is to try and avoid the worst of the problems altogether through best practices.

General Best Practices

As with most things, the key to achieving high performance is education. Developers should know and use good coding and architecture practices, and while some of these guidelines will be obvious to many of you, it’s always worth getting a reminder. Of course, following these guidelines is still not a guarantee that the code will perform well, but it will certainly increase the odds!

  • First of all, you should be aware of the Fallacies of distribute computing in order to be able to avoid the traps they lead you into.
  • Next, you should know your data structures, when it’s appropriate to use them, and what the costs of using them are in terms of memory and access time (are they constant, linear or exponential…).
  • You should understanding the cost of accessing disk vs. the cost of reading data from memory vs. from the network, since the differences in speed can be in orders of magnitude.
  • But most importantly, keep learning about – and adhering to - commonly held development guidelines, like doing the paging and sorting on the database instead of doing it in code, using caching appropriately, making sure the database is properly indexed , minifying and bundling CSS and JavaScript files into a single file to reduce network connections, etc. To get you started, there are resources like Stack Overflow and compilations of tried-and-tested performance advice from other developers. Red Gate has published one such compilation as a free eBook called 50 Ways to Avoid, Find and Fix ASP.NET Performance Issues.

Of course, even when these guidelines are followed and best practices are used, mistakes are bound to happen, and the sooner you catch them the less impact they will have. And more importantly, the easier they’ll be to fix.

I tend to use two tools to catch most problems while the code is being developed. To start with, many performance problems originate at the database level, so let’s tackle that layer first:

SQL Profiler

One of the techniques I use during development is to have SQL profiler constantly open while the application is being used (to use this effectively, more than one monitor is advised to make it easy to monitor your application and database simultaneously), so I can constantly track the queries being executed. By taking a quick look at the SQL activity, I can easily spot some things without much effort:

  • The number of calls being made - If I see many queries in a single request/action, then perhaps there are good candidates for caching, or perhaps there is some lazy loading in action where I should instead use eager loading or prefetching in order to make fewer database calls. ORMs help a great deal during development, but it’s very easy to (unknowingly) abuse the database without realizing what is going on under the hood. Having a profiler active is a great way to way to keep things in line.
  • Slow Queries - if we see queries taking too much time, then perhaps an index is missing, the query is not optimized, or there is a bad condition on a join.
  • Data overload - If too much data is being returned, perhaps paging is either lacking or being mis-handled.
  • Too many physical reads – if I’m seeing a lot of physical reads resulting from queries, the probability of a missing index is high.

One thing to take away from this is that it is important that you have a realistic data set for testing during development, otherwise any problems related to your database (e.g. data structures, configurations, optimizations) will be very hard to spot.

Of course, if your team uses a shared database for development (which is something that you should definitely consider), you should be careful to filter your data so that you’re monitoring only the calls being made by your machine/database user.

Now that you’ve got a way of keeping an eye on your application data store during development, you need a way to monitor the application code itself, so let’s move along.


Another tool that I use a lot while developing is Glimpse. It is an open source ASP.NET module (yes, it’s free) that allows you to easily see a huge amount of information about your application code and server. For example, Glimpse gives you instant visibility into your request data (the request parameters, the configured routes, server variables, sessions), your server’s configuration and environment, the pipeline and methods that were called (including their timings), and AJAX calls – just as a start.

Glimpse does this in a lightweight and un-intrusive way; the data can be inspected right within a web browser, with the information superimposed on the bottom right of the window (Figure 1), ready whenever you need it.

Image 1

Figure 1- Glimpse minimal data seen on the left bottom of the screen

In Figure 2, you can see the data summary in more detail; it has information about both the HTTP request and the code executed on the server to return this particular page.

Image 2

Figure 2 - Glimpse summary window

This summary is always available, and you can expand the data to get more details, as seen in Figure 3. From this example (i.e. the data about what it took to render the page in Figure 3), we can see that the request took a total of 1197 milliseconds to serve, of which 39 were spent on the network transferring information, 84 were spent by the server, and 1074 were spent on the client rendering the page.

Right away, we can see that approximately 88% of the time is spent on the client, so perhaps this is something we should optimize first, since it affects user perception of performance, even if the server is doing its work at admirable speed.

This is a perfect example of the “Don’t Speculate!” principle – minimal effort expended, and we’re already better informed about where to look for performance improvements.

Image 3

Figure 3 - Expanding the summary (browser request)

This is just the tip of the iceberg, as not only does Glimpse provide deeper details than what we’ve briefly looked at here, it supports a plugin system, so you can install extensions to provide details about specific components/systems. For example, instead of using the SQL profiler, we can use an Entity Framework plugin display the SQL command(s) that have been executed by the application, as well as their duration and the parameters (Figure 4). Although this is handy, be aware that the data in Glimpse is not (currently) as rich as the information that SQL profiler provides.

Image 4

Figure 4 - details window. Seing the SQL executed on a request (click for an extended view)

At the time of this writing, taking a quick look at the official nugget repository, we can find 39 Glimpse packages (even if we exclude the core packages, it’s a lot of extensions), so chances are, you’ll find something to help you quickly target exactly the right problems in your own application.

Adding glimpse to your ASP.NET application, is as simple as installing the appropriate package from the official nuget repository, and by default it only works against your local server, so it won’t be enabled on production systems.


Even when code is developed conscientiously, it is almost guaranteed that some things will be slow. For example, after you do load testing, or when your application is required to scale unexpectedly, you might realize that the code doesn’t perform or scale as well as expected. This might happen despite your best intentions, best practices, and most rigorous application of performance optimizations.

As we discussed at the start of the article, when that time comes, you better have some tools that allow you to measure and understand where the time is being spent, so you can focus your optimization efforts where you can really make a difference.

If your application is not yet in production, then bravo for being pre-emptive about writing the best code you can! However, bear in mind that you can only rely on (educated) guesses about how it will be used and how it will behave. Based on the typical profile of your expected users, try to anticipate how they will use the application. Do as many profiling sessions as there are expected usage patterns, and work from there.

If the application is in production, then we have some real data regarding what the most used functions are, so we can focus on them first (optimizing a slow part of the application that is used once or twice a month is one of the traps we mentioned earlier - a waste of resources). You can find these common functions by analyzing application logs or, if your application is using a telemetry application, via data you already have ready to use.

Once you’ve used your data to work out where to start looking, profile and optimize the slowest high-usage functions first (for the biggest gain), and then profile again, and go after the remaining culprits, until optimization is no longer cost effective. Sure, this sounds like a bit of a slog, but I guarantee it’ll be faster than guessing and using timing statements!

Note: The actions I’m describe here can be performed with most of the profilers available on the market (including what’s build into Visual Studio); however I’ll use Red Gate ANTS Performance Profiler to illustrate some of the points, as it’s the only one that lets you relate data access activity directly the .NET code triggering it, which means I can close in on the root cause of problems much faster, and with a minimum of trouble. I’ve also found it to contain a nice balance between ease of use and extensive functionality.

The beauty of using with ANTS Performance Profiler (over manual timing statements or guesswork) is that every run through the profiler assesses the whole application and narrows down the list of potential problems. So no more guesswork, and no more speculation – they just aren’t necessary anymore.

Some Notes on Code Profiling

It’s worth taking a step back to look at profiling in more detail, as it’s arguably the most powerful tool at your disposal. Profiling an application is typically done along two different vectors:

  • Profiling memory usage, in order to find memory leaks, which can severely impact an application’s performance. Or, alternatively, to optimize memory usage (if you use too much memory the application can be constrained by physical or virtual memory). By using less memory, you can reduce memory paging, improve process cache usage and, more importantly, put less stress on the garbage collector.
  • Profiling performance, in order to find performance bottlenecks, and code hotspots (code paths which take more time than others - Figure 5). A good profiler should be able to understand not only where time is being spent in code itself, but also be able to understand when calls are made to external systems (like a call to another server via HTTP), to a relational database, or queuing systems. With this information, if you have some calls that are slow, you can at least identity where the problem is and try to work around it.

And as for calls to database systems, your profiling tool of choice should be able to let you examine the queries that were made (and hopefully the amount of data that has been returned). Ideally it should have the capacity to understand SQL (Figure 6) and be able to group the same queries (with different parameters) so you can concentrate your efforts on optimizing the most critical queries (i.e. the ones most called and with the greatest impact.)

Image 5

Figure 5 - Watching the call tree and viewing the hotspots

Image 6

Figure 6 - viewing the SQL queries executed by the application

Just to be clear, even a powerful tool like ANTS Performance Profiler can sit alongside the SQL Profiler monitoring we covered earlier. The SQL Profiler is a focused tool for a single, specific purpose, and is well suited to continuous monitoring. On the other hand, ANTS Performance Profiler is intended to give you a holistic understanding of your application, with the ability to drill into your .NET code or data access layer.


Let’s briefly run through the salient points we’ve covered:

  1. You should be thinking about performance right when you start writing code.
  2. Performance is a result of user perception, application compilation / configuration, and the code itself (in conjunction with the database and external services).
  3. Education is key to optimizing your code – make sure you know and understand common best practices.
  4. Always keep an eye on how your code is interacting with your database and other external services. You should do this as your developing, and bear it in mind when you get into troubleshooting and dedicated optimization.
  5. Use tools like Glimpse and SQL Profiler to give you constant awareness of how your application is performing, with the data to help you drill down the second you spot a problem.
  6. Inspect and profile your application - don’t use speculation, manual timing statements, or guesswork to figure out where performance problems are. Use the tools at your disposal to get a complete understanding of your whole application, and save yourself a ton of time and pain.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

United States United States
Tiago Pascoal is a Visual Studio ALM Microsoft Most Valuable Professional and a Visual Studio ALM Ranger and a founding member of the Portuguese Software architecture group. With over 13 years’ experience in the software development field, he started his career developing web application servers on multi-platform systems writing software that worked on both Unix and Windows platforms. He consults on software development methodologies and software application lifecycle management and frequently speaks at events about Agile methodologies, architecture and Visual Studio ALM. He sporadically blogs at

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