Site optimisation: analysing bottlenecks (step 3/3)

Modified on Thu, 03 Feb 2022 at 06:37 PM

Now that we have looked at cleaning up your website and using a caching plugin, we are going to look at the last and most technical step: the analysis of bottlenecks in your site. This article is not meant to be a step-by-step follow-up, but rather offers you a number of tools that you can use to check your site yourself for elements that slow down the processes on your site. Just as a chain is as strong as its weakest link, a site is as slow as its slowest calculation task. 

Identifying the problems

It is possible that your site responds slowly. Usually the problem appears to be in a specific action that slows down the other actions on the site. For example, saving a page, changing a specific widget or activating another theme. By figuring this out, you can already remove a lot of possible causes of your problems and focus your attention on patterns. Activating another theme slows down your site? Then you can see if another theme causes the same problem. Adjusting a widget doesn't work? Can another widget work? Try to find as many patterns as possible where you see problems, so you can determine where they arise and take action on them or have them taken.

Error and access logs

With Savvii you have access to your error and access logs which you can also view via sFTP. These logs are a source of information for troubleshooting your site. When you see error messages in your error logs you may assume that your site is not working optimally. In the previous paragraph you see that you can search for patterns as much as possible. If you look at the error logs of your site after you have performed an operation that causes problems, you can often find the error message at that time. You can then analyze this error and for example search on Google for possible causes / other people who have the same problem. As an example:

2017/02/20 13:59:00 [error] ********: *###### FastCGI sent in stderr: "PHP message: PHP Notice:  Undefined variable: background_image in /var/www/******-********/wordpress/current/wp-content/themes/showcase-pro/lib/page-header.php on line 29

In this error you can see that it starts with the date and time. If you look a bit further you see the error message Undefined variable: background_image. If you search for this in Google you will probably find that this is a programming error. A bit further on you can see that this is found in the file page-header.php on line 29. This file is from the theme showcase_pro. If you change the theme, the problem may not come back and you can reasonably assume that the problem is in your theme. Whether you then want to repair the theme, contact the theme makers or use a completely different theme is your next choice. This is just a very simple example of analyzing an error message. If this is too technical it is advisable to use a developer. If you are willing to take further action you can also send us a message, we may be able to help you with the error messages. Don't forget to include the error message.

Query Monitor

Query Monitor is a great plugin to analyze the processes on your site but requires a lot of in-depth and technical knowledge.

    Note: the Query Monitor plugin you only want to install and activate to investigate problems. The plugin analyzes a lot and can cause delays on its own.

External speed test

There are (free) external services that can instruct you to visit and analyse your website. One such page that is widely used by us is . This service visits your website (a number of times) from a location specified by you and provides you with a source of information including load times for complete pages and load times for individual elements. Here you can see how many elements your site is trying to load, how much KB is sent per element and how long this can take. 

For a detailed manual and an explanation of how to read your results, please refer to the WebPagetest help page. . Make sure you enter your website address correctly and choose a test location that reflects the geographical location of your target group.

Additional sources

All steps in this step-by-step plan

Step 1: Cleaning up & updating

Update and clean up all extra elements of your website.

Step 2: caching  

Setting up our Varnish caching and own caching plugins

Step 3: Analysis of bottlenecks (you are here)

A little more technical manual for analyzing further delays

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